Hindawi Publishing CorporationAdvances in Power ElectronicsVolume 2013 Article ID 625130 12 pageshttpdxdoiorg1011552013625130

Research ArticleFault Tolerant Ancillary Function of PowerConverters in Distributed Generation Power Systemwithin a Microgrid Structure

Antonino O Di Tommaso Fabio Genduso Rosario Miceli and Giuseppe Ricco Galluzzo

Department of Energy Informatics and Mathematical Models University of Palermo 90128 Palermo Italy

Correspondence should be addressed to Fabio Genduso gendusodieetunipait

Received 2 August 2012 Revised 6 March 2013 Accepted 2 April 2013

Academic Editor Salem Rahmani

Copyright copy 2013 Antonino O Di Tommaso et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Distributed generation (DG) is deeply changing the existing distribution networks which become very sophisticated and complexincorporating both active and passive equipment The simplification of their management can be obtained assuming a structurewith small networks namely microgrids reproducing in a smaller scale the structure of large networks including productiontransmission and distribution of the electrical energy Power converters in distributed generation systems carry on some differentancillary functions as for example grid synchronization islanding detection fault ride through and so on In view of an optimalutilization of the generated electrical power fault tolerant operation is to be considered as a suitable ancillary function for thenext future This paper presents a complete modeling of fault tolerant inverters able to simulate the main fault type occurrenceand a control algorithm for fault tolerant converters suitable for microgrids After the model description formulated in terms ofhealthy device and leg binary variables and the illustration of the fault tolerant control strategy the paper shows how the controlpreserves power quality when the converter works in the linear range The effectiveness of the proposed approach and control isshown through computer simulations and experimental results

1 Introduction

The exponential penetration of distributed generation (DG)is leading to enormous changes in the conception of theelectrical system management Involved networks are nolonger to be regarded as passive components but integratea growing number of functions such as load managementdemand side management and generation curtailment

Both standalone and grid connected microgrids locallyreproducing the structure of the whole generation and dis-tribution system may be a viable solution to enhance DGbenefits reducing at the same time the drawbacks of DGitself

All the future hypothetical scenarios will lead to greattransformations in the design of power systems with inter-esting implications in different fields of research [1ndash5]

Some problems which arise immediately are the presenceof bidirectional power flow the need for a different designof the power lines and transformers the unwanted islanding

conditions a different protection philosophy and the pos-sibility of a fault tolerant operation to increase the level ofcontinuity

This paper considers fault tolerant operation as a possibleancillary functionThis additional functionmay be importantin autonomous microgrid that cannot benefit from back upinterventions of the traditional distribution network [6]

Since about a decade the fault tolerant converters are thesubject of research and development and their concept hasnow been extended to multilevel converters too because oftheir large number of devices and their redundancy makingthem suitable candidates for such an operation

The present technical literature on the topic is abundanteven not still exhaustive because the research fields are stillup and many open questions are still waiting for significantanswers [7 8]

Among the various aspects themost frequently discussedare control problems [8ndash13] fault diagnosis and protection[6 7 9 14 15] topologies reconfiguration of circuits and

2 Advances in Power Electronics

+

minus

119878119886minus 119878119887minus 119878119888minus

119878119886+ 119878119887+ 119878119888+

119863119886+ 119863119887+ 119863119888+

119863119886minus 119863119887minus 119863119888minus

119880dc

C

C

C

AO B

Figure 1 The VSI topology

controls [4 8 13 16 17] and effect of fault tolerant operationson the main network [14 18] and on the loads with a specialreference to evaluation of performance of AC electrical drives[7 9ndash11]

This paper presents first a mathematical model ableto represent both the behavior of a faulted converter andthe fault tolerant operating mode Subsequently a controlstrategy that can generate a substantially symmetrical three-phase output and the related implementation algorithm areexaminedThe fault tolerant operation is therefore consideredin the context of a grid converter operation analyzing thesystem behavior and the operating limits of the same one inorder to guarantee an acceptable level of power quality In thisscenario some immediate indications on levels of transmittedpower and performance deviations with respect to a classicalgrid converter are givenThe validation of the control strategyand of the used algorithm is verified through simulations andexperimental tests of a prototype built within the SDESLABat the University of Palermo

The next sections are organized as followsSection 2 deals with the general model of the inverter

Section 3 shows the simulation of the open-circuit fault Sec-tion 4 illustrates the fault tolerant mode and the correspond-ing control algorithm and displays the simulation resultsSection 5 deals with the specific case of a grid converterwithin a microgrid and outlines some considerations aboutthe transmitted power and the current distortion and theneed for a higher level of theDCLink voltage Section 6 showsthe experimental results obtained by tests on the realizedprototype Finally Section 7 summarizes the conclusions

2 The General Inverter Model

21 The General Model for Healthy Mode For the generalmodel of the Voltage Source Inverter in faulty and unfaultylet us consider the circuit of Figure 1 presenting the generaltopology of a VSI

The current circulation on free-wheeling diodes is alsoconsidered as also illustrated in the references [19ndash21]

For each controllable device a switching function isdefined in terms of gate pulse For the jth upper device it isfor example

119878119895+ = 1 if driving pulse is given0 otherwise (with 119895 = 119860 119861 119862)

(1)

A complementary switching function is defined for thelower device 119878119895minus The effective turning on of the device isconditioned by the current sign In fact an upper controllabledevice can effectively be turned on only if the load current ispositive conversely a lower device can be turned on only ifthe same current is negative In general current not beingconducted by controlled devices is conducted by the free-wheeling diodes Even if diodes are not controllable devicesswitching functions may be defined for them also by takinginto account the current sign For example an upper diodeconducting the negative current is turned on only if the lowercontrollable device is off In this way the switching functionfor the upper diode is

119863119895+ = 119878119895minus otimes (119894119895 lt 0) (2)

In a similar manner for the lower diode it is

119863119895minus = 119878119895+ otimes (119894119895 gt 0) (3)

By summarizing all the previous considerations two gener-alized switching functions may be defined

119878119895+ = [119878119895+ otimes (119894119895 gt 0)] oplus [119878119895minus otimes (119894119895 lt 0)]

119878119895minus = [119878119895minus otimes (119894119895 lt 0)] oplus [119878119895+ otimes (119894119895 gt 0)]

(4)

Considering now the converter topology output voltagewith respect to the 119874 point as sketched in Figure 1 may bewritten as

V119895119874 = (119878119895+ minus 119878119895minus)119906DC2 119895 = 119860 119861 119862 (5)

If the load impedances are balanced the phase to neutralvoltages have the well-known expressions

V119895119873 = V119895119874 minussum119896=119895 V119896119874

3 119895 = 119860 119861 119862 (6)

The load currents can be found from the equations

V119895119873 = 119877119894119895 + 119871119889119894119895

119889119905+ 119890119895119873

(7)

For a complete inverter model the equations describing theDC link circuit transient must be considered In particularthe expression of the DC link voltage is

119862119889119906DC119889119905

= 1198940 minus sum

119896=119895

119894119896119878119896+ (8)

Advances in Power Electronics 3

and 1198940 is given by

119906 minus 119906DC = 11987701198940 + 11987101198891198940

119889119905 (9)

Equations (4)ndash(9) constitute themodel of a VSI in the healthymode

The Section 22 considers the modified converter modelat faulty mode

22 The General Model for the Faulty Mode Recent studieshave shown as up than the 80 of converter faults are due tosingle or multiple device failures [22]

Every power structure designer strives to remain wellwithin the operating limits of the power device as specifiedby the IGBT manufacturer However there are componentfailures either of the power switching device or of supportingcomponents that result in one or more IGBT power devicefailures When the IGBT power devices fail under certaincircumstances the failure can result in the rupture of thepower module and extensive damage to the surroundingpower components [23]

Typically failures are manifest as counterblow destruc-tion as in the case of short circuit of silicon packed devices orby losing driver pulse occurring if driver circuit or its powersupply are invalid so that no trigger pulse is sent to the gate[8] Open-circuit faults generally do not cause shutdown ofthe system but degrade its performance [10 21]

Some of the gate drive failure can result from breaking ofpassive components (resistors and capacity) or from a driftof their values for which the behavior of the driver doesnot meet the original specifications With regard to shortcircuits or defects caused by overcurrent a crucial parameteris the passing through energy 1198682119905 that during time causes adegradation of the materials employed in the construction ofthe components

Short circuit faults have a very fast evolution and ingeneral no software algorithm is able to detect them in theshort time required to interrupt and insulate the faulted zonefrom the rest of the system For this reason they are generallymanaged directly with hardware additional device or circuitsand interruptedwith ultrafast fuses taking care that these lastones should not introduce any additional inductances in themain circuit

Short circuits and ruptures that do not imply any furtherdamage to the remaining part of the power circuit evolve toan open circuit condition For this reason only open circuitfaults are considered here

Multiple device faults are less frequent but may be alsosignificant if the inverter leg is an integrated packaged oneHowever the presented model will also consider the caseof multiple devices damage Furthermore thanks to thefollowed approach in all the examined cases an inverterreconfiguration for the fault tolerant mode can be simulated

In this section the single device faults for drive failure andalso for diode breakdown are considered

If a controllable upper device goes to a drive failurecondition in this case the 119878119895+ switching function is alwayszero A positive current cannot be conducted by any device of

the faulted phase The negative current may instead circulatein the upper diode and in the lower controlled device Startingfrom diode conduction if the lower device is turned off acommutation phenomenon appears then the diode currentturns to zero while the transistor current rises up In this casethe general switching function becomes

119878119895+ = [119878119895minus otimes (119894119895 lt 0)]

119878119895minus = [119878119895minus otimes (119894119895 lt 0)]

(10)

In particular 119878119895+ considers only the upper diode conductionwhile 119878119895minus denotes the lower transistor conduction Similarconsideration applies when the faulted device is the lower Infact in this case the general switching functions become

119878119895+ = [119878119895+ otimes (119894119895 gt 0)]

119878119895minus = [119878119895+ otimes (119894119895 gt 0)]

(11)

For the general case the introduction of a healthy devicebinary variable (HDBV) is useful It is defined as follows

ℎ119895plusmn = 1 if the upper (+) lower (minus) device is healthy0 otherwise

(12)

The introduction HDBVs makes the definition of the gener-alized (ie in faulty and unfaulty mode) switching functionvery simple In fact

119878119895+ = [ℎ119895+119878119895+ otimes (119894119895 gt 0)] oplus [ℎ119895minus119878119895minus otimes (119894119895 lt 0)]

119878119895minus = [ℎ119895minus119878119895minus otimes (119894119895 lt 0)] oplus [ℎ119895+119878119895+ otimes (119894119895 gt 0)]

(13)

that is in a general simulation scheme the fault behavior ismodeled simply with the product of 119878119895plusmn by ℎ119895plusmn

The same principle applies when both the transistor andthe diode are broken but the first expression of (10) nowcontains two incompatible conditions However to get acorrect simulation result the signal of (10) may be used toreset the integrators of (7) In other words when the lowerpower device is turned off the load current is forced to zero

The loss of entire converter leg does not introduce anydifference because the approach with healthy device binaryvariable also allows an easy and affordable modeling ininverter reconfiguration for themanagement of the converterin fault-tolerant mode With this aim the healthy leg binaryvariables (HLBV) are then introduced as follows

ℎ119895 = ℎ119895+ oplus ℎ119895minus (14)

In reconfiguration after the fault diagnosis the faultedleg is disabled and the load terminal of the faulted phase isconnected to the middle point of the DC link allowing thecurrent circulation by means of bidirectional switches Thereconfigured inverter assumes the topology of a B4 circuit(see Figure 2)

4 Advances in Power Electronics

+

minus

119878119887minus 119878119888minus

119878119887+ 119878119888+

119863119887+ 119863119888+

119863119887minus 119863119888minus

119880dc

C

C

C

C

A B

BO

Figure 2 The reconfigured inverter after the fault (B4 topology)

In previous papers of the authors [14 18 21 24ndash27]this reconfiguration has been extensively investigated andthe general model of the reconfigured inverter has been alsopresentedThis model will consist of the following equations

1198801 =1

119862int

119905

0

(1198940 minus StkHkik) 119889119905

1198802 =1

119862int

119905

0

(1198940 minus [S119905119896H119896 minus 1

119905H119896] ik) 119889119905(15)

for the partial DC link voltages with

H119896 = (ℎ119860 0 0

0 ℎ119861 0

0 0 ℎ119862

)

k119896119873 = 119880DCTH119896S119896 minus TH11989611198802

(16)

for the inverter output voltages with

T = 13(

2 minus1 minus1

minus1 2 minus1

minus1 minus1 2

) (17)

The load (grid) equations remain unchanged

3 Simulation of the Faults

Simulations of faults are made with the help of the previousmodel whose equations are implemented thanks to theMatlab-Simulink software package In the simulation a VSIwith a 300V DC link voltage is hypothesized Simulationresults are illustrated in the figures below

Figure 3 shows the output voltage on the faulted phasewhen a driver failure for an upper device appears whileFigure 4 shows the currents on the load after fault

Simulations show clearly the positive current interruptionand the negative current which flows through the diode

During the current interruption the average value of thephase voltage is zero (the instantaneous value is only made

032 0325 033 0335 034 0345 035 0355Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119886

(V)

Figure 3 Voltage on load faulted phase for upper device drivefailure

0325 033 0335 034 0345 035 0355 036 0365 037Time (s)

Curr

ents

(A)

minus4

minus3

minus2

minus1

0

1

2

3

4

Figure 4 Currents on the load after fault

up of a series of voltage spikes) Other currents on unfaultyphases become phase opposite while the applied voltages onit are half of the line to line voltage with a different sign

Figure 5 shows instead the voltage on an unfaultedphase

Figures 6 and 7 show respectively the same simulationresults when the fault regards both the device and the free-wheeling diode

Voltage is very similar to that of the previous analyzedcase except for a higher number of spikes Currents areinstead quite different being composed of a series of negativepulse due to commutation of the lower transistor Theunfaulted phase voltages are very similar to the previous onesand for this reason are not reported here

4 The Control Strategy for the FaultTolerant Operation

41 The Fault Tolerant Control Arrangement In the case ofloss of an entire leg the only reconnection of the faulted

Advances in Power Electronics 5

0275 028 0285 029 0295 03 0305 031 0315Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119887

(V)

Figure 5 Voltage on an unfaulted phase

031 0315 032 0325 033 0335 034 0345 035Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119887

(V)

Figure 6 Faulty phase voltage after transistor and diode havebroken

Table 1 Synthesis of the postfault reference voltages

Healthy 119880ref Phase 119860 fault Phase 119861 fault Phase 119862 fault119906119860 0 minus119906119862 119906119861

119906119861 119906119862 0 minus119906119860

119906119862 minus119906119861 119906119860 0

phase to DC link middle point does not ensure a correctoperation In particular the current peak amplitude of thefaulted phase results lowers by a factorradic3 In order to obtaina balanced currents system the voltage references used in themodulation process must be changed

In the case of a grid converter its capability to maintaina set of symmetrical voltages is very important for thepower quality in view to limit as possible disturbancespropagation into the grid avoiding oversized apparatuses totheir mitigation

The new modified set of reference voltages in the fault-tolerant mode should then present a minimal inverse com-ponent

033 0335 034 0345 035 0355 036 0365 037Time (s)

minus3

minus2

minus1

0

1

2

3

4

Curr

ents

(A)

Figure 7 Load currents after broken transistor and diodeThe new reference voltages consist of a set of two

sinusoidal signals controlling the healthy legsSuppose now that the signals corresponding phasors are

119880ref1 = 119880119909 exp (1198950)

119880ref2 = 119880119909 exp (minus119895120593) (18)

For the fault cases on phases A B and C respectively theinverse component of this reference system is

119880inv119860 = 0 + 120572119880ref1 + 1205722119880ref2

119880inv119861 = 119880ref1 + 1205720 + 1205722119880ref2

119880inv119862 = 119880ref1 + 120572119880ref2 + 12057220

(19)

By calculating the module of the inverse components itfollows that

1003816100381610038161003816119880inv1003816100381610038161003816 =radic2119880119909

radic1 + cos(120593 plusmn 21205873) (20)

in which the sign ldquo+rdquo is for a fault on phaseA and C while thesign ldquominusrdquo is for a fault on phase B In both cases the minimuminverse factor is reached for120593plusmn21205873 = 120587 that is for120593 = plusmn1205873and it results just |119880inv| = 0

Hence in a fault tolerant converter the new referenceshave equal amplitude and a 60-degree phase displacement

Furthermore the new references can be built followingthe suggestion of Table 1

Therefore the general expression of the reference voltages(119906lowast119896 with 119896 = 119860 119861 119862) for healthy and faulted conditions is

119906lowast119860 = 119906119860ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119862119906119861 minus ℎ119861119906119862)

119906lowast119861 = 119906119861ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119860119906119862 minus ℎ119862119906119860)

119906lowast119862 = 119906119862ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119861119906119860 minus ℎ119860119906119861)

(21)

where 119906119895 is the set of normal symmetrical three-phasereference voltages

6 Advances in Power Electronics

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881A

N(V

)

(a)

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881CN

(V)

(b)

Figure 8 Phase voltages at unfaulted and faulted converter leg

051 052 053 054 055 056 057 058 059Time (s)

minus10

minus8

minus6

minus4

minus2

0

2

4

6

8

10

119894 ABC

(A)

Figure 9 Load current before and after faults

Equation (21) may be also written in vector notation

ulowast = 120582u + radic3u times h (22)

where 120582 = ℎ119860ℎ119861ℎ119862 = det(H119896)The modified reference voltage are very simple to be

implemented on microprocessors and diagnostic signals onthe converters can be used to synthesize the new postfaultreference voltages

In (21) the general term 120582u is the reference for the healthycase while the vectors cross product radic3(u times h) is the newreference in the faulted case The factor radic3 guarantees theidentity of the voltage and current amplitude even after thefault has occurred

Note that the cross product termradic3(utimesh) should be 1205872clockwise rotated if the converter is a grid connected thusmaintaining the synchronization between converter and gridvoltages In this case the reference voltages system expressedin vector form results

ulowast = 120582u + radic3 (u times h) 119890minus119895(1205872) (23)

The first advantage of (23) is a close integration of thediagnostic signals directly in the control for the inverterreconfiguration another advantage is to make the fault andreconfiguration transparent to the main control system In

fact any regulating action of external variables can providea three-phase voltage reference that will be then manipulatedaccording to (23) in order to generate the correct referenceIn other words the only reason for which the control systemcan be affected by the fault is the unavoidable DC link voltageripple (as discussed later) and its effect on the current

42 The Control Simulation Control simulation results areillustrated in the following figures showing how the faultcondition is managed by themodel with themodified controlstrategy in order to guarantee the minimal derating in powerquality

Figure 8 shows the converter phase voltage measured atunfaulted (a) and faulted leg (b) after the faults occurredresulting their first harmonics a symmetrical system evenafter the fault

The voltage waveforms are quite different from those withunfaulted converter condition and the faulted leg voltageexhibits the greatest difference

Figure 9 shows converter currents before and after faultoccurrence with the instantaneous modification of the con-verter references The residual current imbalance after faultis due to the alternating components in the DC-link voltagedepending on the current amplitude and on the outputfrequency In general the voltage oscillation in single DCcapacitors does not affect significantly the entire value of theDC link voltage and the general converter performance

Postfault currents exhibit a phase jump due to reconfig-uration unless this is compensated Figure 10 shows insteadthe effect on load currents with the phase jump correctionintroduced in (23)

The linear region of the converter during the fault is ineach case restricted Linear range is quite important in orderto achieve minimal currents asymmetry

Figure 11 shows a higher load current distortion andunbalance during overmodulation (ie with an amplitudemodulation index higher than 05 in the faulted case)

Figure 12 shows the voltage imbalance on the twoDC linkcapacitors

5 Simulation of a Grid Converter with FaultTolerant Operation

The illustrated simulation was made for a standalone con-verter In the case of a grid converter fed by a DG source

Advances in Power Electronics 7

035 0355 036 0365 037 0375 038minus6

minus4

minus2

0

2

4

6

Time (s)

Phas

e cur

rent

s (A

)

Figure 10 Load currents before and after fault with phase jumpcorrection

138 139 14 141 142 143 144 145 146 147

minus10

minus5

0

5

10

Time (s)

Curr

ents

(A)

Figure 11 Distorted and unbalanced load currents with higherdistortion during faulted condition in overmodulation mode

045 05 055 06 065 07 075 08 085 09140

142

144

146

148

150

152

154

156

158

Time (s)

1198801

and1198802

DC

link

volta

ges (

V)

Figure 12 Voltage unbalance through DC link ca pacitors

the system and the control are more complicated Howeverno modification of the classical control structure of a gridconverter is needed Figure 13 shows the simplified schemeof the control structure for a grid converter control in whichactive and reactive power are managed via current controlloop and DC link voltage loop A complete description ofthe grid converter control system and of some other differentsolutions is given in [28 29]

The control scheme allows active 119875 and reactive power 119876to be managed separately by decoupling DQ channels for thecurrent control so that P depends on 119894119863 and Q depends on119894119876 via previous proper grid synchronization via PLLThe DClink voltage control is also performed

In the example of this section the grid filter is notoptimally designed with the aim to put better in evidencesome aspect of the fault tolerant grid converter behavior

The simulation assumes the occurrence of a fault thefast reconfiguration of the converter and the decrease ofthe active power injected into the grid Subsequently thereactive power transferred to the grid is vanished It is evidentthat despite the active power decrease there is a greaterdistortion of the output current as it is seen in Figures 14and 15 (also with reference to the 119894119863 and 119894119876 components)due to the increased voltage ripple on the DC link Thisoscillation is natural and the control system can only fix itsmean value forced by the set pointThe simulation shows wellas vanishing the delivered reactive power the DC link voltageoscillation decreases with benefit for both the input and thegrid current that exhibit a lower distortion as evident fromFigures 16 17 18 19 and 20

It is worthwhile to remark that for avoiding overmodula-tion the fault tolerant converter has aDC link voltage 25ndash30greater than that of a traditional grid converter

6 Experimental Results

Experimental results were made available in the case of thefault tolerant mode where the reconfiguration makes theconverter operation more safe for a normal laboratory test Itwas not possible to test the converter as a grid-converter oneso the tests on the fault tolerant operation have been made byfeeding an induction motor and registering output voltagesand currents

For the experimental test a customary benchmark basedon an INFRANOR power converter and a dSPACE controlboard has been built and set up

The converter used in the test bench is a commercialfrequency converter whose control board has been replacedby a customary one designed to be driven by the dSPACEcontrol board and converting the TTL gating pulses to theldquoline driverdquo type of the INFRANOR converter (see Figure 21)

In the practical realization of a fault tolerant convertersome issues are mandatory to be taken into account Triacsfor the current path closure may suffer for a 119889V119889119905 not suf-ficient immunity having therefore unwanted switchings Asolution to this problem can be the choice of a different bidi-rectional controllable switch In particular the combinationof power diodes in a bridge configuration with an auxiliary

8 Advances in Power Electronics

From DG sourceThree-phase

network

119875 control

119876lowast

119875lowast

+ minus

PLL

119894119863119894119876

Currentcontroller

and PWM119876 control

PI

PI

PI

Decoupled currentcontroller

DQOABC

Converter

wL119880119902

119880119902

119880119889

119880119889119880119889lowast

119880119902lowastminuswL

119894119876lowast

119894119876lowast

119894119863lowast

119894119863lowast

119894119876

119894119863

119880dclowast

119880dc119880dc[

w

w

Figure 13 The control structure of a grid converter

102 104 106 108 11 112 114 116 118 12

minus10

minus5

0

5

10

119905 (s)

Out

put c

urre

nt (A

)

Figure 14 Current decrease after fault and reconfiguration

IGBT is able to reach bidirectional current circulation (seeFigure 22 for topology details) A fault detection algorithmbased on the elaboration of load current signal has alsobeen implemented An extensive technical literature (see eg[4 5]) exists on fault detection but its discussion here is outof the scopes of this paper

The fed induction motor is a two-pole three-phase squir-rel cage whose nameplate is reported in Table 2

A digital oscilloscope with two differential probes (up toa 25-MHz bandwidth) and 3 accuracy has been used toregister voltage and current waveforms Measurements datawere stored in the computer hosting the dSPACE board withthe help of ldquoOctaverdquo software

Fault emulation have been realized with the help of solidstate relays and connectors being driven from the dSPACEboard and software interface In this way it was possible to

0 05 1 15 2 25 3minus15

minus10

minus5

0

5

10

15

119905 (s)

119894 119863119894 119876

(A)

Figure 15 119894119863 (blue) and 119894119876 (green) current components

test the behavior of the fault-tolerant converter in all possiblecondition without a real disruption of the power devices

Figures 23 24 and 25 shows respectively the measure-ments of voltage on faulty and unfaulty phases and themeasurement of the currents before and after fault andreconfiguration

This final comparison validates the proposed generalmodel of VSI in healthy and faulty mode implementedalgorithm

7 Conclusions

The use of fault-tolerant systems is essential for the optimaldevelopment of electrical power production by renewablesources as well as for the achievement of high reliability

Advances in Power Electronics 9

155 156 157 158 159 16 161 162 163 164

minus5

minus4

minus3

minus2

minus1

0

1

2

3

4

5

119905 (s)

Out

put c

urre

nt (A

)

Figure 16 After fault current zoom

226 227 228 229 23 231 232 233 234minus3

minus2

minus1

0

1

2

119905 (s)

Out

put c

urre

nt (A

)

Figure 17 After fault current with no reactive power

16 165 17 175 18 185

minus200

minus100

0

100

200

Grid

vol

tage

(V)

grid

curr

ent (

A)

minus10

minus5

0

5

10

119905 (s)

Figure 18 Phase voltage (blue dashed) and current (green continu-ous) with and without Q transmission

16 165 17 175 18 185 19 195 2

minus3

minus2

minus1

0

1

2

3

4

119905 (s)

119894 119863119894 119876

(A)

Figure 19 119894119863 and 119894119876 transient after vanishing Q

15 155 16 165 17 175 18 185 19 195 205

06

07

08

09

1

11

12

13

14

15

119905 (s)

Inpu

t cur

rent

(A)

Figure 20 Transient on 1198940 after vanishing Q

Table 2 Test bench induction motor nameplates

Ratings ValuePower 55 kWSpeed 2870 rpmFrequency 50ndash60HzTorque 183NmVoltage 400VCurrent 13 APoles 2

and power quality fundamental for both end users and gridmanager

Fault tolerant converters require intelligent real-timedetection algorithms of incoming failures easy to implementeven on low cost hardware such as microcontrollers orPegasus

In this paper the authors have considered the faulttolerant operation of an inverter for distributed generation

10 Advances in Power Electronics

Figure 21 Picture of the realized test bench

Figure 22 A bidirectional switch realized with diode and IGBT

system seen as an ancillary complementary function inaddiction to the classical ones already developedThe generalinverter model here presented in the paper is suitable anduseful for the simulation of faults and fault-tolerant operationof a VSI The presented model is very helpful to predicttransient phenomena due to faults occurrence Switchingfunction definition has been extended in order to cover thecondition of diode turning on and open fault occurrenceThe introduction of HDBVs and HLBVs allows for theconstruction of a unified model suitable for simulations withequation solver tools This makes the simulations affordableand at the same time fast in their operation

The implementation algorithm is very suitable in largecontext as grid connected converter for DG because it istransparent to the action of the main power control andsynchronization

Numerical simulations presented in the paper have con-sidered both a standalone and a grid converter In order toguarantee minimal power quality degradation the followingconsiderations apply in the converter control

(i) over modulation must be avoided(ii) for this reason both a reduction of the transmitted

active power and vanishing the reactive power aremandatory

(iii) a 25ndash30 greater DC link voltage with respect totraditional value must be chosen

The control has been also verified with experimental resultsin the case of reconfigurable operation Comparison of

004 006 008 01 012 014 016 018 02Time (s)

minus250

minus200

minus150

minus100

minus50

0

50

100

150

200

250

119881119886

(V)

Figure 23 Measurement of faulty phase voltage before and after thefault

005 01 015Time (s)

minus300

minus200

minus100

0

100

200119881119887

(V)

Figure 24 Measurement of unfaulty phase voltage before and afterthe fault

002 004 006 008 01 012 014 016 018 02Time (s)

minus10

minus5

0

5

10

119894 ABC

(A)

Figure 25Measurement of phase currents before and after the fault

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

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International Journal of

2 Advances in Power Electronics

+

minus

119878119886minus 119878119887minus 119878119888minus

119878119886+ 119878119887+ 119878119888+

119863119886+ 119863119887+ 119863119888+

119863119886minus 119863119887minus 119863119888minus

119880dc

C

C

C

AO B

Figure 1 The VSI topology

controls [4 8 13 16 17] and effect of fault tolerant operationson the main network [14 18] and on the loads with a specialreference to evaluation of performance of AC electrical drives[7 9ndash11]

This paper presents first a mathematical model ableto represent both the behavior of a faulted converter andthe fault tolerant operating mode Subsequently a controlstrategy that can generate a substantially symmetrical three-phase output and the related implementation algorithm areexaminedThe fault tolerant operation is therefore consideredin the context of a grid converter operation analyzing thesystem behavior and the operating limits of the same one inorder to guarantee an acceptable level of power quality In thisscenario some immediate indications on levels of transmittedpower and performance deviations with respect to a classicalgrid converter are givenThe validation of the control strategyand of the used algorithm is verified through simulations andexperimental tests of a prototype built within the SDESLABat the University of Palermo

The next sections are organized as followsSection 2 deals with the general model of the inverter

Section 3 shows the simulation of the open-circuit fault Sec-tion 4 illustrates the fault tolerant mode and the correspond-ing control algorithm and displays the simulation resultsSection 5 deals with the specific case of a grid converterwithin a microgrid and outlines some considerations aboutthe transmitted power and the current distortion and theneed for a higher level of theDCLink voltage Section 6 showsthe experimental results obtained by tests on the realizedprototype Finally Section 7 summarizes the conclusions

2 The General Inverter Model

21 The General Model for Healthy Mode For the generalmodel of the Voltage Source Inverter in faulty and unfaultylet us consider the circuit of Figure 1 presenting the generaltopology of a VSI

The current circulation on free-wheeling diodes is alsoconsidered as also illustrated in the references [19ndash21]

For each controllable device a switching function isdefined in terms of gate pulse For the jth upper device it isfor example

119878119895+ = 1 if driving pulse is given0 otherwise (with 119895 = 119860 119861 119862)

(1)

A complementary switching function is defined for thelower device 119878119895minus The effective turning on of the device isconditioned by the current sign In fact an upper controllabledevice can effectively be turned on only if the load current ispositive conversely a lower device can be turned on only ifthe same current is negative In general current not beingconducted by controlled devices is conducted by the free-wheeling diodes Even if diodes are not controllable devicesswitching functions may be defined for them also by takinginto account the current sign For example an upper diodeconducting the negative current is turned on only if the lowercontrollable device is off In this way the switching functionfor the upper diode is

119863119895+ = 119878119895minus otimes (119894119895 lt 0) (2)

In a similar manner for the lower diode it is

119863119895minus = 119878119895+ otimes (119894119895 gt 0) (3)

By summarizing all the previous considerations two gener-alized switching functions may be defined

119878119895+ = [119878119895+ otimes (119894119895 gt 0)] oplus [119878119895minus otimes (119894119895 lt 0)]

119878119895minus = [119878119895minus otimes (119894119895 lt 0)] oplus [119878119895+ otimes (119894119895 gt 0)]

(4)

Considering now the converter topology output voltagewith respect to the 119874 point as sketched in Figure 1 may bewritten as

V119895119874 = (119878119895+ minus 119878119895minus)119906DC2 119895 = 119860 119861 119862 (5)

If the load impedances are balanced the phase to neutralvoltages have the well-known expressions

V119895119873 = V119895119874 minussum119896=119895 V119896119874

3 119895 = 119860 119861 119862 (6)

The load currents can be found from the equations

V119895119873 = 119877119894119895 + 119871119889119894119895

119889119905+ 119890119895119873

(7)

For a complete inverter model the equations describing theDC link circuit transient must be considered In particularthe expression of the DC link voltage is

119862119889119906DC119889119905

= 1198940 minus sum

119896=119895

119894119896119878119896+ (8)

Advances in Power Electronics 3

and 1198940 is given by

119906 minus 119906DC = 11987701198940 + 11987101198891198940

119889119905 (9)

Equations (4)ndash(9) constitute themodel of a VSI in the healthymode

The Section 22 considers the modified converter modelat faulty mode

22 The General Model for the Faulty Mode Recent studieshave shown as up than the 80 of converter faults are due tosingle or multiple device failures [22]

Every power structure designer strives to remain wellwithin the operating limits of the power device as specifiedby the IGBT manufacturer However there are componentfailures either of the power switching device or of supportingcomponents that result in one or more IGBT power devicefailures When the IGBT power devices fail under certaincircumstances the failure can result in the rupture of thepower module and extensive damage to the surroundingpower components [23]

Typically failures are manifest as counterblow destruc-tion as in the case of short circuit of silicon packed devices orby losing driver pulse occurring if driver circuit or its powersupply are invalid so that no trigger pulse is sent to the gate[8] Open-circuit faults generally do not cause shutdown ofthe system but degrade its performance [10 21]

Some of the gate drive failure can result from breaking ofpassive components (resistors and capacity) or from a driftof their values for which the behavior of the driver doesnot meet the original specifications With regard to shortcircuits or defects caused by overcurrent a crucial parameteris the passing through energy 1198682119905 that during time causes adegradation of the materials employed in the construction ofthe components

Short circuit faults have a very fast evolution and ingeneral no software algorithm is able to detect them in theshort time required to interrupt and insulate the faulted zonefrom the rest of the system For this reason they are generallymanaged directly with hardware additional device or circuitsand interruptedwith ultrafast fuses taking care that these lastones should not introduce any additional inductances in themain circuit

Short circuits and ruptures that do not imply any furtherdamage to the remaining part of the power circuit evolve toan open circuit condition For this reason only open circuitfaults are considered here

Multiple device faults are less frequent but may be alsosignificant if the inverter leg is an integrated packaged oneHowever the presented model will also consider the caseof multiple devices damage Furthermore thanks to thefollowed approach in all the examined cases an inverterreconfiguration for the fault tolerant mode can be simulated

In this section the single device faults for drive failure andalso for diode breakdown are considered

If a controllable upper device goes to a drive failurecondition in this case the 119878119895+ switching function is alwayszero A positive current cannot be conducted by any device of

the faulted phase The negative current may instead circulatein the upper diode and in the lower controlled device Startingfrom diode conduction if the lower device is turned off acommutation phenomenon appears then the diode currentturns to zero while the transistor current rises up In this casethe general switching function becomes

119878119895+ = [119878119895minus otimes (119894119895 lt 0)]

119878119895minus = [119878119895minus otimes (119894119895 lt 0)]

(10)

In particular 119878119895+ considers only the upper diode conductionwhile 119878119895minus denotes the lower transistor conduction Similarconsideration applies when the faulted device is the lower Infact in this case the general switching functions become

119878119895+ = [119878119895+ otimes (119894119895 gt 0)]

119878119895minus = [119878119895+ otimes (119894119895 gt 0)]

(11)

For the general case the introduction of a healthy devicebinary variable (HDBV) is useful It is defined as follows

ℎ119895plusmn = 1 if the upper (+) lower (minus) device is healthy0 otherwise

(12)

The introduction HDBVs makes the definition of the gener-alized (ie in faulty and unfaulty mode) switching functionvery simple In fact

119878119895+ = [ℎ119895+119878119895+ otimes (119894119895 gt 0)] oplus [ℎ119895minus119878119895minus otimes (119894119895 lt 0)]

119878119895minus = [ℎ119895minus119878119895minus otimes (119894119895 lt 0)] oplus [ℎ119895+119878119895+ otimes (119894119895 gt 0)]

(13)

that is in a general simulation scheme the fault behavior ismodeled simply with the product of 119878119895plusmn by ℎ119895plusmn

The same principle applies when both the transistor andthe diode are broken but the first expression of (10) nowcontains two incompatible conditions However to get acorrect simulation result the signal of (10) may be used toreset the integrators of (7) In other words when the lowerpower device is turned off the load current is forced to zero

The loss of entire converter leg does not introduce anydifference because the approach with healthy device binaryvariable also allows an easy and affordable modeling ininverter reconfiguration for themanagement of the converterin fault-tolerant mode With this aim the healthy leg binaryvariables (HLBV) are then introduced as follows

ℎ119895 = ℎ119895+ oplus ℎ119895minus (14)

In reconfiguration after the fault diagnosis the faultedleg is disabled and the load terminal of the faulted phase isconnected to the middle point of the DC link allowing thecurrent circulation by means of bidirectional switches Thereconfigured inverter assumes the topology of a B4 circuit(see Figure 2)

4 Advances in Power Electronics

+

minus

119878119887minus 119878119888minus

119878119887+ 119878119888+

119863119887+ 119863119888+

119863119887minus 119863119888minus

119880dc

C

C

C

C

A B

BO

Figure 2 The reconfigured inverter after the fault (B4 topology)

In previous papers of the authors [14 18 21 24ndash27]this reconfiguration has been extensively investigated andthe general model of the reconfigured inverter has been alsopresentedThis model will consist of the following equations

1198801 =1

119862int

119905

0

(1198940 minus StkHkik) 119889119905

1198802 =1

119862int

119905

0

(1198940 minus [S119905119896H119896 minus 1

119905H119896] ik) 119889119905(15)

for the partial DC link voltages with

H119896 = (ℎ119860 0 0

0 ℎ119861 0

0 0 ℎ119862

)

k119896119873 = 119880DCTH119896S119896 minus TH11989611198802

(16)

for the inverter output voltages with

T = 13(

2 minus1 minus1

minus1 2 minus1

minus1 minus1 2

) (17)

The load (grid) equations remain unchanged

3 Simulation of the Faults

Simulations of faults are made with the help of the previousmodel whose equations are implemented thanks to theMatlab-Simulink software package In the simulation a VSIwith a 300V DC link voltage is hypothesized Simulationresults are illustrated in the figures below

Figure 3 shows the output voltage on the faulted phasewhen a driver failure for an upper device appears whileFigure 4 shows the currents on the load after fault

Simulations show clearly the positive current interruptionand the negative current which flows through the diode

During the current interruption the average value of thephase voltage is zero (the instantaneous value is only made

032 0325 033 0335 034 0345 035 0355Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119886

(V)

Figure 3 Voltage on load faulted phase for upper device drivefailure

0325 033 0335 034 0345 035 0355 036 0365 037Time (s)

Curr

ents

(A)

minus4

minus3

minus2

minus1

0

1

2

3

4

Figure 4 Currents on the load after fault

up of a series of voltage spikes) Other currents on unfaultyphases become phase opposite while the applied voltages onit are half of the line to line voltage with a different sign

Figure 5 shows instead the voltage on an unfaultedphase

Figures 6 and 7 show respectively the same simulationresults when the fault regards both the device and the free-wheeling diode

Voltage is very similar to that of the previous analyzedcase except for a higher number of spikes Currents areinstead quite different being composed of a series of negativepulse due to commutation of the lower transistor Theunfaulted phase voltages are very similar to the previous onesand for this reason are not reported here

4 The Control Strategy for the FaultTolerant Operation

41 The Fault Tolerant Control Arrangement In the case ofloss of an entire leg the only reconnection of the faulted

Advances in Power Electronics 5

0275 028 0285 029 0295 03 0305 031 0315Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119887

(V)

Figure 5 Voltage on an unfaulted phase

031 0315 032 0325 033 0335 034 0345 035Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119887

(V)

Figure 6 Faulty phase voltage after transistor and diode havebroken

Table 1 Synthesis of the postfault reference voltages

Healthy 119880ref Phase 119860 fault Phase 119861 fault Phase 119862 fault119906119860 0 minus119906119862 119906119861

119906119861 119906119862 0 minus119906119860

119906119862 minus119906119861 119906119860 0

phase to DC link middle point does not ensure a correctoperation In particular the current peak amplitude of thefaulted phase results lowers by a factorradic3 In order to obtaina balanced currents system the voltage references used in themodulation process must be changed

In the case of a grid converter its capability to maintaina set of symmetrical voltages is very important for thepower quality in view to limit as possible disturbancespropagation into the grid avoiding oversized apparatuses totheir mitigation

The new modified set of reference voltages in the fault-tolerant mode should then present a minimal inverse com-ponent

033 0335 034 0345 035 0355 036 0365 037Time (s)

minus3

minus2

minus1

0

1

2

3

4

Curr

ents

(A)

Figure 7 Load currents after broken transistor and diodeThe new reference voltages consist of a set of two

sinusoidal signals controlling the healthy legsSuppose now that the signals corresponding phasors are

119880ref1 = 119880119909 exp (1198950)

119880ref2 = 119880119909 exp (minus119895120593) (18)

For the fault cases on phases A B and C respectively theinverse component of this reference system is

119880inv119860 = 0 + 120572119880ref1 + 1205722119880ref2

119880inv119861 = 119880ref1 + 1205720 + 1205722119880ref2

119880inv119862 = 119880ref1 + 120572119880ref2 + 12057220

(19)

By calculating the module of the inverse components itfollows that

1003816100381610038161003816119880inv1003816100381610038161003816 =radic2119880119909

radic1 + cos(120593 plusmn 21205873) (20)

in which the sign ldquo+rdquo is for a fault on phaseA and C while thesign ldquominusrdquo is for a fault on phase B In both cases the minimuminverse factor is reached for120593plusmn21205873 = 120587 that is for120593 = plusmn1205873and it results just |119880inv| = 0

Hence in a fault tolerant converter the new referenceshave equal amplitude and a 60-degree phase displacement

Furthermore the new references can be built followingthe suggestion of Table 1

Therefore the general expression of the reference voltages(119906lowast119896 with 119896 = 119860 119861 119862) for healthy and faulted conditions is

119906lowast119860 = 119906119860ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119862119906119861 minus ℎ119861119906119862)

119906lowast119861 = 119906119861ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119860119906119862 minus ℎ119862119906119860)

119906lowast119862 = 119906119862ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119861119906119860 minus ℎ119860119906119861)

(21)

where 119906119895 is the set of normal symmetrical three-phasereference voltages

6 Advances in Power Electronics

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881A

N(V

)

(a)

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881CN

(V)

(b)

Figure 8 Phase voltages at unfaulted and faulted converter leg

051 052 053 054 055 056 057 058 059Time (s)

minus10

minus8

minus6

minus4

minus2

0

2

4

6

8

10

119894 ABC

(A)

Figure 9 Load current before and after faults

Equation (21) may be also written in vector notation

ulowast = 120582u + radic3u times h (22)

where 120582 = ℎ119860ℎ119861ℎ119862 = det(H119896)The modified reference voltage are very simple to be

implemented on microprocessors and diagnostic signals onthe converters can be used to synthesize the new postfaultreference voltages

In (21) the general term 120582u is the reference for the healthycase while the vectors cross product radic3(u times h) is the newreference in the faulted case The factor radic3 guarantees theidentity of the voltage and current amplitude even after thefault has occurred

Note that the cross product termradic3(utimesh) should be 1205872clockwise rotated if the converter is a grid connected thusmaintaining the synchronization between converter and gridvoltages In this case the reference voltages system expressedin vector form results

ulowast = 120582u + radic3 (u times h) 119890minus119895(1205872) (23)

The first advantage of (23) is a close integration of thediagnostic signals directly in the control for the inverterreconfiguration another advantage is to make the fault andreconfiguration transparent to the main control system In

fact any regulating action of external variables can providea three-phase voltage reference that will be then manipulatedaccording to (23) in order to generate the correct referenceIn other words the only reason for which the control systemcan be affected by the fault is the unavoidable DC link voltageripple (as discussed later) and its effect on the current

42 The Control Simulation Control simulation results areillustrated in the following figures showing how the faultcondition is managed by themodel with themodified controlstrategy in order to guarantee the minimal derating in powerquality

Figure 8 shows the converter phase voltage measured atunfaulted (a) and faulted leg (b) after the faults occurredresulting their first harmonics a symmetrical system evenafter the fault

The voltage waveforms are quite different from those withunfaulted converter condition and the faulted leg voltageexhibits the greatest difference

Figure 9 shows converter currents before and after faultoccurrence with the instantaneous modification of the con-verter references The residual current imbalance after faultis due to the alternating components in the DC-link voltagedepending on the current amplitude and on the outputfrequency In general the voltage oscillation in single DCcapacitors does not affect significantly the entire value of theDC link voltage and the general converter performance

Postfault currents exhibit a phase jump due to reconfig-uration unless this is compensated Figure 10 shows insteadthe effect on load currents with the phase jump correctionintroduced in (23)

The linear region of the converter during the fault is ineach case restricted Linear range is quite important in orderto achieve minimal currents asymmetry

Figure 11 shows a higher load current distortion andunbalance during overmodulation (ie with an amplitudemodulation index higher than 05 in the faulted case)

Figure 12 shows the voltage imbalance on the twoDC linkcapacitors

5 Simulation of a Grid Converter with FaultTolerant Operation

The illustrated simulation was made for a standalone con-verter In the case of a grid converter fed by a DG source

Advances in Power Electronics 7

035 0355 036 0365 037 0375 038minus6

minus4

minus2

0

2

4

6

Time (s)

Phas

e cur

rent

s (A

)

Figure 10 Load currents before and after fault with phase jumpcorrection

138 139 14 141 142 143 144 145 146 147

minus10

minus5

0

5

10

Time (s)

Curr

ents

(A)

Figure 11 Distorted and unbalanced load currents with higherdistortion during faulted condition in overmodulation mode

045 05 055 06 065 07 075 08 085 09140

142

144

146

148

150

152

154

156

158

Time (s)

1198801

and1198802

DC

link

volta

ges (

V)

Figure 12 Voltage unbalance through DC link ca pacitors

the system and the control are more complicated Howeverno modification of the classical control structure of a gridconverter is needed Figure 13 shows the simplified schemeof the control structure for a grid converter control in whichactive and reactive power are managed via current controlloop and DC link voltage loop A complete description ofthe grid converter control system and of some other differentsolutions is given in [28 29]

The control scheme allows active 119875 and reactive power 119876to be managed separately by decoupling DQ channels for thecurrent control so that P depends on 119894119863 and Q depends on119894119876 via previous proper grid synchronization via PLLThe DClink voltage control is also performed

In the example of this section the grid filter is notoptimally designed with the aim to put better in evidencesome aspect of the fault tolerant grid converter behavior

The simulation assumes the occurrence of a fault thefast reconfiguration of the converter and the decrease ofthe active power injected into the grid Subsequently thereactive power transferred to the grid is vanished It is evidentthat despite the active power decrease there is a greaterdistortion of the output current as it is seen in Figures 14and 15 (also with reference to the 119894119863 and 119894119876 components)due to the increased voltage ripple on the DC link Thisoscillation is natural and the control system can only fix itsmean value forced by the set pointThe simulation shows wellas vanishing the delivered reactive power the DC link voltageoscillation decreases with benefit for both the input and thegrid current that exhibit a lower distortion as evident fromFigures 16 17 18 19 and 20

It is worthwhile to remark that for avoiding overmodula-tion the fault tolerant converter has aDC link voltage 25ndash30greater than that of a traditional grid converter

6 Experimental Results

Experimental results were made available in the case of thefault tolerant mode where the reconfiguration makes theconverter operation more safe for a normal laboratory test Itwas not possible to test the converter as a grid-converter oneso the tests on the fault tolerant operation have been made byfeeding an induction motor and registering output voltagesand currents

For the experimental test a customary benchmark basedon an INFRANOR power converter and a dSPACE controlboard has been built and set up

The converter used in the test bench is a commercialfrequency converter whose control board has been replacedby a customary one designed to be driven by the dSPACEcontrol board and converting the TTL gating pulses to theldquoline driverdquo type of the INFRANOR converter (see Figure 21)

In the practical realization of a fault tolerant convertersome issues are mandatory to be taken into account Triacsfor the current path closure may suffer for a 119889V119889119905 not suf-ficient immunity having therefore unwanted switchings Asolution to this problem can be the choice of a different bidi-rectional controllable switch In particular the combinationof power diodes in a bridge configuration with an auxiliary

8 Advances in Power Electronics

From DG sourceThree-phase

network

119875 control

119876lowast

119875lowast

+ minus

PLL

119894119863119894119876

Currentcontroller

and PWM119876 control

PI

PI

PI

Decoupled currentcontroller

DQOABC

Converter

wL119880119902

119880119902

119880119889

119880119889119880119889lowast

119880119902lowastminuswL

119894119876lowast

119894119876lowast

119894119863lowast

119894119863lowast

119894119876

119894119863

119880dclowast

119880dc119880dc[

w

w

Figure 13 The control structure of a grid converter

102 104 106 108 11 112 114 116 118 12

minus10

minus5

0

5

10

119905 (s)

Out

put c

urre

nt (A

)

Figure 14 Current decrease after fault and reconfiguration

IGBT is able to reach bidirectional current circulation (seeFigure 22 for topology details) A fault detection algorithmbased on the elaboration of load current signal has alsobeen implemented An extensive technical literature (see eg[4 5]) exists on fault detection but its discussion here is outof the scopes of this paper

The fed induction motor is a two-pole three-phase squir-rel cage whose nameplate is reported in Table 2

A digital oscilloscope with two differential probes (up toa 25-MHz bandwidth) and 3 accuracy has been used toregister voltage and current waveforms Measurements datawere stored in the computer hosting the dSPACE board withthe help of ldquoOctaverdquo software

Fault emulation have been realized with the help of solidstate relays and connectors being driven from the dSPACEboard and software interface In this way it was possible to

0 05 1 15 2 25 3minus15

minus10

minus5

0

5

10

15

119905 (s)

119894 119863119894 119876

(A)

Figure 15 119894119863 (blue) and 119894119876 (green) current components

test the behavior of the fault-tolerant converter in all possiblecondition without a real disruption of the power devices

Figures 23 24 and 25 shows respectively the measure-ments of voltage on faulty and unfaulty phases and themeasurement of the currents before and after fault andreconfiguration

This final comparison validates the proposed generalmodel of VSI in healthy and faulty mode implementedalgorithm

7 Conclusions

The use of fault-tolerant systems is essential for the optimaldevelopment of electrical power production by renewablesources as well as for the achievement of high reliability

Advances in Power Electronics 9

155 156 157 158 159 16 161 162 163 164

minus5

minus4

minus3

minus2

minus1

0

1

2

3

4

5

119905 (s)

Out

put c

urre

nt (A

)

Figure 16 After fault current zoom

226 227 228 229 23 231 232 233 234minus3

minus2

minus1

0

1

2

119905 (s)

Out

put c

urre

nt (A

)

Figure 17 After fault current with no reactive power

16 165 17 175 18 185

minus200

minus100

0

100

200

Grid

vol

tage

(V)

grid

curr

ent (

A)

minus10

minus5

0

5

10

119905 (s)

Figure 18 Phase voltage (blue dashed) and current (green continu-ous) with and without Q transmission

16 165 17 175 18 185 19 195 2

minus3

minus2

minus1

0

1

2

3

4

119905 (s)

119894 119863119894 119876

(A)

Figure 19 119894119863 and 119894119876 transient after vanishing Q

15 155 16 165 17 175 18 185 19 195 205

06

07

08

09

1

11

12

13

14

15

119905 (s)

Inpu

t cur

rent

(A)

Figure 20 Transient on 1198940 after vanishing Q

Table 2 Test bench induction motor nameplates

Ratings ValuePower 55 kWSpeed 2870 rpmFrequency 50ndash60HzTorque 183NmVoltage 400VCurrent 13 APoles 2

and power quality fundamental for both end users and gridmanager

Fault tolerant converters require intelligent real-timedetection algorithms of incoming failures easy to implementeven on low cost hardware such as microcontrollers orPegasus

In this paper the authors have considered the faulttolerant operation of an inverter for distributed generation

10 Advances in Power Electronics

Figure 21 Picture of the realized test bench

Figure 22 A bidirectional switch realized with diode and IGBT

system seen as an ancillary complementary function inaddiction to the classical ones already developedThe generalinverter model here presented in the paper is suitable anduseful for the simulation of faults and fault-tolerant operationof a VSI The presented model is very helpful to predicttransient phenomena due to faults occurrence Switchingfunction definition has been extended in order to cover thecondition of diode turning on and open fault occurrenceThe introduction of HDBVs and HLBVs allows for theconstruction of a unified model suitable for simulations withequation solver tools This makes the simulations affordableand at the same time fast in their operation

The implementation algorithm is very suitable in largecontext as grid connected converter for DG because it istransparent to the action of the main power control andsynchronization

Numerical simulations presented in the paper have con-sidered both a standalone and a grid converter In order toguarantee minimal power quality degradation the followingconsiderations apply in the converter control

(i) over modulation must be avoided(ii) for this reason both a reduction of the transmitted

active power and vanishing the reactive power aremandatory

(iii) a 25ndash30 greater DC link voltage with respect totraditional value must be chosen

The control has been also verified with experimental resultsin the case of reconfigurable operation Comparison of

004 006 008 01 012 014 016 018 02Time (s)

minus250

minus200

minus150

minus100

minus50

0

50

100

150

200

250

119881119886

(V)

Figure 23 Measurement of faulty phase voltage before and after thefault

005 01 015Time (s)

minus300

minus200

minus100

0

100

200119881119887

(V)

Figure 24 Measurement of unfaulty phase voltage before and afterthe fault

002 004 006 008 01 012 014 016 018 02Time (s)

minus10

minus5

0

5

10

119894 ABC

(A)

Figure 25Measurement of phase currents before and after the fault

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

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Submit your manuscripts athttpwwwhindawicom

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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DistributedSensor Networks

International Journal of

Advances in Power Electronics 3

and 1198940 is given by

119906 minus 119906DC = 11987701198940 + 11987101198891198940

119889119905 (9)

Equations (4)ndash(9) constitute themodel of a VSI in the healthymode

The Section 22 considers the modified converter modelat faulty mode

22 The General Model for the Faulty Mode Recent studieshave shown as up than the 80 of converter faults are due tosingle or multiple device failures [22]

Every power structure designer strives to remain wellwithin the operating limits of the power device as specifiedby the IGBT manufacturer However there are componentfailures either of the power switching device or of supportingcomponents that result in one or more IGBT power devicefailures When the IGBT power devices fail under certaincircumstances the failure can result in the rupture of thepower module and extensive damage to the surroundingpower components [23]

Typically failures are manifest as counterblow destruc-tion as in the case of short circuit of silicon packed devices orby losing driver pulse occurring if driver circuit or its powersupply are invalid so that no trigger pulse is sent to the gate[8] Open-circuit faults generally do not cause shutdown ofthe system but degrade its performance [10 21]

Some of the gate drive failure can result from breaking ofpassive components (resistors and capacity) or from a driftof their values for which the behavior of the driver doesnot meet the original specifications With regard to shortcircuits or defects caused by overcurrent a crucial parameteris the passing through energy 1198682119905 that during time causes adegradation of the materials employed in the construction ofthe components

Short circuit faults have a very fast evolution and ingeneral no software algorithm is able to detect them in theshort time required to interrupt and insulate the faulted zonefrom the rest of the system For this reason they are generallymanaged directly with hardware additional device or circuitsand interruptedwith ultrafast fuses taking care that these lastones should not introduce any additional inductances in themain circuit

Short circuits and ruptures that do not imply any furtherdamage to the remaining part of the power circuit evolve toan open circuit condition For this reason only open circuitfaults are considered here

Multiple device faults are less frequent but may be alsosignificant if the inverter leg is an integrated packaged oneHowever the presented model will also consider the caseof multiple devices damage Furthermore thanks to thefollowed approach in all the examined cases an inverterreconfiguration for the fault tolerant mode can be simulated

In this section the single device faults for drive failure andalso for diode breakdown are considered

If a controllable upper device goes to a drive failurecondition in this case the 119878119895+ switching function is alwayszero A positive current cannot be conducted by any device of

the faulted phase The negative current may instead circulatein the upper diode and in the lower controlled device Startingfrom diode conduction if the lower device is turned off acommutation phenomenon appears then the diode currentturns to zero while the transistor current rises up In this casethe general switching function becomes

119878119895+ = [119878119895minus otimes (119894119895 lt 0)]

119878119895minus = [119878119895minus otimes (119894119895 lt 0)]

(10)

In particular 119878119895+ considers only the upper diode conductionwhile 119878119895minus denotes the lower transistor conduction Similarconsideration applies when the faulted device is the lower Infact in this case the general switching functions become

119878119895+ = [119878119895+ otimes (119894119895 gt 0)]

119878119895minus = [119878119895+ otimes (119894119895 gt 0)]

(11)

For the general case the introduction of a healthy devicebinary variable (HDBV) is useful It is defined as follows

ℎ119895plusmn = 1 if the upper (+) lower (minus) device is healthy0 otherwise

(12)

The introduction HDBVs makes the definition of the gener-alized (ie in faulty and unfaulty mode) switching functionvery simple In fact

119878119895+ = [ℎ119895+119878119895+ otimes (119894119895 gt 0)] oplus [ℎ119895minus119878119895minus otimes (119894119895 lt 0)]

119878119895minus = [ℎ119895minus119878119895minus otimes (119894119895 lt 0)] oplus [ℎ119895+119878119895+ otimes (119894119895 gt 0)]

(13)

that is in a general simulation scheme the fault behavior ismodeled simply with the product of 119878119895plusmn by ℎ119895plusmn

The same principle applies when both the transistor andthe diode are broken but the first expression of (10) nowcontains two incompatible conditions However to get acorrect simulation result the signal of (10) may be used toreset the integrators of (7) In other words when the lowerpower device is turned off the load current is forced to zero

The loss of entire converter leg does not introduce anydifference because the approach with healthy device binaryvariable also allows an easy and affordable modeling ininverter reconfiguration for themanagement of the converterin fault-tolerant mode With this aim the healthy leg binaryvariables (HLBV) are then introduced as follows

ℎ119895 = ℎ119895+ oplus ℎ119895minus (14)

In reconfiguration after the fault diagnosis the faultedleg is disabled and the load terminal of the faulted phase isconnected to the middle point of the DC link allowing thecurrent circulation by means of bidirectional switches Thereconfigured inverter assumes the topology of a B4 circuit(see Figure 2)

4 Advances in Power Electronics

+

minus

119878119887minus 119878119888minus

119878119887+ 119878119888+

119863119887+ 119863119888+

119863119887minus 119863119888minus

119880dc

C

C

C

C

A B

BO

Figure 2 The reconfigured inverter after the fault (B4 topology)

In previous papers of the authors [14 18 21 24ndash27]this reconfiguration has been extensively investigated andthe general model of the reconfigured inverter has been alsopresentedThis model will consist of the following equations

1198801 =1

119862int

119905

0

(1198940 minus StkHkik) 119889119905

1198802 =1

119862int

119905

0

(1198940 minus [S119905119896H119896 minus 1

119905H119896] ik) 119889119905(15)

for the partial DC link voltages with

H119896 = (ℎ119860 0 0

0 ℎ119861 0

0 0 ℎ119862

)

k119896119873 = 119880DCTH119896S119896 minus TH11989611198802

(16)

for the inverter output voltages with

T = 13(

2 minus1 minus1

minus1 2 minus1

minus1 minus1 2

) (17)

The load (grid) equations remain unchanged

3 Simulation of the Faults

Simulations of faults are made with the help of the previousmodel whose equations are implemented thanks to theMatlab-Simulink software package In the simulation a VSIwith a 300V DC link voltage is hypothesized Simulationresults are illustrated in the figures below

Figure 3 shows the output voltage on the faulted phasewhen a driver failure for an upper device appears whileFigure 4 shows the currents on the load after fault

Simulations show clearly the positive current interruptionand the negative current which flows through the diode

During the current interruption the average value of thephase voltage is zero (the instantaneous value is only made

032 0325 033 0335 034 0345 035 0355Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119886

(V)

Figure 3 Voltage on load faulted phase for upper device drivefailure

0325 033 0335 034 0345 035 0355 036 0365 037Time (s)

Curr

ents

(A)

minus4

minus3

minus2

minus1

0

1

2

3

4

Figure 4 Currents on the load after fault

up of a series of voltage spikes) Other currents on unfaultyphases become phase opposite while the applied voltages onit are half of the line to line voltage with a different sign

Figure 5 shows instead the voltage on an unfaultedphase

Figures 6 and 7 show respectively the same simulationresults when the fault regards both the device and the free-wheeling diode

Voltage is very similar to that of the previous analyzedcase except for a higher number of spikes Currents areinstead quite different being composed of a series of negativepulse due to commutation of the lower transistor Theunfaulted phase voltages are very similar to the previous onesand for this reason are not reported here

4 The Control Strategy for the FaultTolerant Operation

41 The Fault Tolerant Control Arrangement In the case ofloss of an entire leg the only reconnection of the faulted

Advances in Power Electronics 5

0275 028 0285 029 0295 03 0305 031 0315Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119887

(V)

Figure 5 Voltage on an unfaulted phase

031 0315 032 0325 033 0335 034 0345 035Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119887

(V)

Figure 6 Faulty phase voltage after transistor and diode havebroken

Table 1 Synthesis of the postfault reference voltages

Healthy 119880ref Phase 119860 fault Phase 119861 fault Phase 119862 fault119906119860 0 minus119906119862 119906119861

119906119861 119906119862 0 minus119906119860

119906119862 minus119906119861 119906119860 0

phase to DC link middle point does not ensure a correctoperation In particular the current peak amplitude of thefaulted phase results lowers by a factorradic3 In order to obtaina balanced currents system the voltage references used in themodulation process must be changed

In the case of a grid converter its capability to maintaina set of symmetrical voltages is very important for thepower quality in view to limit as possible disturbancespropagation into the grid avoiding oversized apparatuses totheir mitigation

The new modified set of reference voltages in the fault-tolerant mode should then present a minimal inverse com-ponent

033 0335 034 0345 035 0355 036 0365 037Time (s)

minus3

minus2

minus1

0

1

2

3

4

Curr

ents

(A)

Figure 7 Load currents after broken transistor and diodeThe new reference voltages consist of a set of two

sinusoidal signals controlling the healthy legsSuppose now that the signals corresponding phasors are

119880ref1 = 119880119909 exp (1198950)

119880ref2 = 119880119909 exp (minus119895120593) (18)

For the fault cases on phases A B and C respectively theinverse component of this reference system is

119880inv119860 = 0 + 120572119880ref1 + 1205722119880ref2

119880inv119861 = 119880ref1 + 1205720 + 1205722119880ref2

119880inv119862 = 119880ref1 + 120572119880ref2 + 12057220

(19)

By calculating the module of the inverse components itfollows that

1003816100381610038161003816119880inv1003816100381610038161003816 =radic2119880119909

radic1 + cos(120593 plusmn 21205873) (20)

in which the sign ldquo+rdquo is for a fault on phaseA and C while thesign ldquominusrdquo is for a fault on phase B In both cases the minimuminverse factor is reached for120593plusmn21205873 = 120587 that is for120593 = plusmn1205873and it results just |119880inv| = 0

Hence in a fault tolerant converter the new referenceshave equal amplitude and a 60-degree phase displacement

Furthermore the new references can be built followingthe suggestion of Table 1

Therefore the general expression of the reference voltages(119906lowast119896 with 119896 = 119860 119861 119862) for healthy and faulted conditions is

119906lowast119860 = 119906119860ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119862119906119861 minus ℎ119861119906119862)

119906lowast119861 = 119906119861ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119860119906119862 minus ℎ119862119906119860)

119906lowast119862 = 119906119862ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119861119906119860 minus ℎ119860119906119861)

(21)

where 119906119895 is the set of normal symmetrical three-phasereference voltages

6 Advances in Power Electronics

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881A

N(V

)

(a)

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881CN

(V)

(b)

Figure 8 Phase voltages at unfaulted and faulted converter leg

051 052 053 054 055 056 057 058 059Time (s)

minus10

minus8

minus6

minus4

minus2

0

2

4

6

8

10

119894 ABC

(A)

Figure 9 Load current before and after faults

Equation (21) may be also written in vector notation

ulowast = 120582u + radic3u times h (22)

where 120582 = ℎ119860ℎ119861ℎ119862 = det(H119896)The modified reference voltage are very simple to be

implemented on microprocessors and diagnostic signals onthe converters can be used to synthesize the new postfaultreference voltages

In (21) the general term 120582u is the reference for the healthycase while the vectors cross product radic3(u times h) is the newreference in the faulted case The factor radic3 guarantees theidentity of the voltage and current amplitude even after thefault has occurred

Note that the cross product termradic3(utimesh) should be 1205872clockwise rotated if the converter is a grid connected thusmaintaining the synchronization between converter and gridvoltages In this case the reference voltages system expressedin vector form results

ulowast = 120582u + radic3 (u times h) 119890minus119895(1205872) (23)

The first advantage of (23) is a close integration of thediagnostic signals directly in the control for the inverterreconfiguration another advantage is to make the fault andreconfiguration transparent to the main control system In

fact any regulating action of external variables can providea three-phase voltage reference that will be then manipulatedaccording to (23) in order to generate the correct referenceIn other words the only reason for which the control systemcan be affected by the fault is the unavoidable DC link voltageripple (as discussed later) and its effect on the current

42 The Control Simulation Control simulation results areillustrated in the following figures showing how the faultcondition is managed by themodel with themodified controlstrategy in order to guarantee the minimal derating in powerquality

Figure 8 shows the converter phase voltage measured atunfaulted (a) and faulted leg (b) after the faults occurredresulting their first harmonics a symmetrical system evenafter the fault

The voltage waveforms are quite different from those withunfaulted converter condition and the faulted leg voltageexhibits the greatest difference

Figure 9 shows converter currents before and after faultoccurrence with the instantaneous modification of the con-verter references The residual current imbalance after faultis due to the alternating components in the DC-link voltagedepending on the current amplitude and on the outputfrequency In general the voltage oscillation in single DCcapacitors does not affect significantly the entire value of theDC link voltage and the general converter performance

Postfault currents exhibit a phase jump due to reconfig-uration unless this is compensated Figure 10 shows insteadthe effect on load currents with the phase jump correctionintroduced in (23)

The linear region of the converter during the fault is ineach case restricted Linear range is quite important in orderto achieve minimal currents asymmetry

Figure 11 shows a higher load current distortion andunbalance during overmodulation (ie with an amplitudemodulation index higher than 05 in the faulted case)

Figure 12 shows the voltage imbalance on the twoDC linkcapacitors

5 Simulation of a Grid Converter with FaultTolerant Operation

The illustrated simulation was made for a standalone con-verter In the case of a grid converter fed by a DG source

Advances in Power Electronics 7

035 0355 036 0365 037 0375 038minus6

minus4

minus2

0

2

4

6

Time (s)

Phas

e cur

rent

s (A

)

Figure 10 Load currents before and after fault with phase jumpcorrection

138 139 14 141 142 143 144 145 146 147

minus10

minus5

0

5

10

Time (s)

Curr

ents

(A)

Figure 11 Distorted and unbalanced load currents with higherdistortion during faulted condition in overmodulation mode

045 05 055 06 065 07 075 08 085 09140

142

144

146

148

150

152

154

156

158

Time (s)

1198801

and1198802

DC

link

volta

ges (

V)

Figure 12 Voltage unbalance through DC link ca pacitors

the system and the control are more complicated Howeverno modification of the classical control structure of a gridconverter is needed Figure 13 shows the simplified schemeof the control structure for a grid converter control in whichactive and reactive power are managed via current controlloop and DC link voltage loop A complete description ofthe grid converter control system and of some other differentsolutions is given in [28 29]

The control scheme allows active 119875 and reactive power 119876to be managed separately by decoupling DQ channels for thecurrent control so that P depends on 119894119863 and Q depends on119894119876 via previous proper grid synchronization via PLLThe DClink voltage control is also performed

In the example of this section the grid filter is notoptimally designed with the aim to put better in evidencesome aspect of the fault tolerant grid converter behavior

The simulation assumes the occurrence of a fault thefast reconfiguration of the converter and the decrease ofthe active power injected into the grid Subsequently thereactive power transferred to the grid is vanished It is evidentthat despite the active power decrease there is a greaterdistortion of the output current as it is seen in Figures 14and 15 (also with reference to the 119894119863 and 119894119876 components)due to the increased voltage ripple on the DC link Thisoscillation is natural and the control system can only fix itsmean value forced by the set pointThe simulation shows wellas vanishing the delivered reactive power the DC link voltageoscillation decreases with benefit for both the input and thegrid current that exhibit a lower distortion as evident fromFigures 16 17 18 19 and 20

It is worthwhile to remark that for avoiding overmodula-tion the fault tolerant converter has aDC link voltage 25ndash30greater than that of a traditional grid converter

6 Experimental Results

Experimental results were made available in the case of thefault tolerant mode where the reconfiguration makes theconverter operation more safe for a normal laboratory test Itwas not possible to test the converter as a grid-converter oneso the tests on the fault tolerant operation have been made byfeeding an induction motor and registering output voltagesand currents

For the experimental test a customary benchmark basedon an INFRANOR power converter and a dSPACE controlboard has been built and set up

The converter used in the test bench is a commercialfrequency converter whose control board has been replacedby a customary one designed to be driven by the dSPACEcontrol board and converting the TTL gating pulses to theldquoline driverdquo type of the INFRANOR converter (see Figure 21)

In the practical realization of a fault tolerant convertersome issues are mandatory to be taken into account Triacsfor the current path closure may suffer for a 119889V119889119905 not suf-ficient immunity having therefore unwanted switchings Asolution to this problem can be the choice of a different bidi-rectional controllable switch In particular the combinationof power diodes in a bridge configuration with an auxiliary

8 Advances in Power Electronics

From DG sourceThree-phase

network

119875 control

119876lowast

119875lowast

+ minus

PLL

119894119863119894119876

Currentcontroller

and PWM119876 control

PI

PI

PI

Decoupled currentcontroller

DQOABC

Converter

wL119880119902

119880119902

119880119889

119880119889119880119889lowast

119880119902lowastminuswL

119894119876lowast

119894119876lowast

119894119863lowast

119894119863lowast

119894119876

119894119863

119880dclowast

119880dc119880dc[

w

w

Figure 13 The control structure of a grid converter

102 104 106 108 11 112 114 116 118 12

minus10

minus5

0

5

10

119905 (s)

Out

put c

urre

nt (A

)

Figure 14 Current decrease after fault and reconfiguration

IGBT is able to reach bidirectional current circulation (seeFigure 22 for topology details) A fault detection algorithmbased on the elaboration of load current signal has alsobeen implemented An extensive technical literature (see eg[4 5]) exists on fault detection but its discussion here is outof the scopes of this paper

The fed induction motor is a two-pole three-phase squir-rel cage whose nameplate is reported in Table 2

A digital oscilloscope with two differential probes (up toa 25-MHz bandwidth) and 3 accuracy has been used toregister voltage and current waveforms Measurements datawere stored in the computer hosting the dSPACE board withthe help of ldquoOctaverdquo software

Fault emulation have been realized with the help of solidstate relays and connectors being driven from the dSPACEboard and software interface In this way it was possible to

0 05 1 15 2 25 3minus15

minus10

minus5

0

5

10

15

119905 (s)

119894 119863119894 119876

(A)

Figure 15 119894119863 (blue) and 119894119876 (green) current components

test the behavior of the fault-tolerant converter in all possiblecondition without a real disruption of the power devices

Figures 23 24 and 25 shows respectively the measure-ments of voltage on faulty and unfaulty phases and themeasurement of the currents before and after fault andreconfiguration

This final comparison validates the proposed generalmodel of VSI in healthy and faulty mode implementedalgorithm

7 Conclusions

The use of fault-tolerant systems is essential for the optimaldevelopment of electrical power production by renewablesources as well as for the achievement of high reliability

Advances in Power Electronics 9

155 156 157 158 159 16 161 162 163 164

minus5

minus4

minus3

minus2

minus1

0

1

2

3

4

5

119905 (s)

Out

put c

urre

nt (A

)

Figure 16 After fault current zoom

226 227 228 229 23 231 232 233 234minus3

minus2

minus1

0

1

2

119905 (s)

Out

put c

urre

nt (A

)

Figure 17 After fault current with no reactive power

16 165 17 175 18 185

minus200

minus100

0

100

200

Grid

vol

tage

(V)

grid

curr

ent (

A)

minus10

minus5

0

5

10

119905 (s)

Figure 18 Phase voltage (blue dashed) and current (green continu-ous) with and without Q transmission

16 165 17 175 18 185 19 195 2

minus3

minus2

minus1

0

1

2

3

4

119905 (s)

119894 119863119894 119876

(A)

Figure 19 119894119863 and 119894119876 transient after vanishing Q

15 155 16 165 17 175 18 185 19 195 205

06

07

08

09

1

11

12

13

14

15

119905 (s)

Inpu

t cur

rent

(A)

Figure 20 Transient on 1198940 after vanishing Q

Table 2 Test bench induction motor nameplates

Ratings ValuePower 55 kWSpeed 2870 rpmFrequency 50ndash60HzTorque 183NmVoltage 400VCurrent 13 APoles 2

and power quality fundamental for both end users and gridmanager

Fault tolerant converters require intelligent real-timedetection algorithms of incoming failures easy to implementeven on low cost hardware such as microcontrollers orPegasus

In this paper the authors have considered the faulttolerant operation of an inverter for distributed generation

10 Advances in Power Electronics

Figure 21 Picture of the realized test bench

Figure 22 A bidirectional switch realized with diode and IGBT

system seen as an ancillary complementary function inaddiction to the classical ones already developedThe generalinverter model here presented in the paper is suitable anduseful for the simulation of faults and fault-tolerant operationof a VSI The presented model is very helpful to predicttransient phenomena due to faults occurrence Switchingfunction definition has been extended in order to cover thecondition of diode turning on and open fault occurrenceThe introduction of HDBVs and HLBVs allows for theconstruction of a unified model suitable for simulations withequation solver tools This makes the simulations affordableand at the same time fast in their operation

The implementation algorithm is very suitable in largecontext as grid connected converter for DG because it istransparent to the action of the main power control andsynchronization

Numerical simulations presented in the paper have con-sidered both a standalone and a grid converter In order toguarantee minimal power quality degradation the followingconsiderations apply in the converter control

(i) over modulation must be avoided(ii) for this reason both a reduction of the transmitted

active power and vanishing the reactive power aremandatory

(iii) a 25ndash30 greater DC link voltage with respect totraditional value must be chosen

The control has been also verified with experimental resultsin the case of reconfigurable operation Comparison of

004 006 008 01 012 014 016 018 02Time (s)

minus250

minus200

minus150

minus100

minus50

0

50

100

150

200

250

119881119886

(V)

Figure 23 Measurement of faulty phase voltage before and after thefault

005 01 015Time (s)

minus300

minus200

minus100

0

100

200119881119887

(V)

Figure 24 Measurement of unfaulty phase voltage before and afterthe fault

002 004 006 008 01 012 014 016 018 02Time (s)

minus10

minus5

0

5

10

119894 ABC

(A)

Figure 25Measurement of phase currents before and after the fault

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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DistributedSensor Networks

International Journal of

4 Advances in Power Electronics

+

minus

119878119887minus 119878119888minus

119878119887+ 119878119888+

119863119887+ 119863119888+

119863119887minus 119863119888minus

119880dc

C

C

C

C

A B

BO

Figure 2 The reconfigured inverter after the fault (B4 topology)

In previous papers of the authors [14 18 21 24ndash27]this reconfiguration has been extensively investigated andthe general model of the reconfigured inverter has been alsopresentedThis model will consist of the following equations

1198801 =1

119862int

119905

0

(1198940 minus StkHkik) 119889119905

1198802 =1

119862int

119905

0

(1198940 minus [S119905119896H119896 minus 1

119905H119896] ik) 119889119905(15)

for the partial DC link voltages with

H119896 = (ℎ119860 0 0

0 ℎ119861 0

0 0 ℎ119862

)

k119896119873 = 119880DCTH119896S119896 minus TH11989611198802

(16)

for the inverter output voltages with

T = 13(

2 minus1 minus1

minus1 2 minus1

minus1 minus1 2

) (17)

The load (grid) equations remain unchanged

3 Simulation of the Faults

Simulations of faults are made with the help of the previousmodel whose equations are implemented thanks to theMatlab-Simulink software package In the simulation a VSIwith a 300V DC link voltage is hypothesized Simulationresults are illustrated in the figures below

Figure 3 shows the output voltage on the faulted phasewhen a driver failure for an upper device appears whileFigure 4 shows the currents on the load after fault

Simulations show clearly the positive current interruptionand the negative current which flows through the diode

During the current interruption the average value of thephase voltage is zero (the instantaneous value is only made

032 0325 033 0335 034 0345 035 0355Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119886

(V)

Figure 3 Voltage on load faulted phase for upper device drivefailure

0325 033 0335 034 0345 035 0355 036 0365 037Time (s)

Curr

ents

(A)

minus4

minus3

minus2

minus1

0

1

2

3

4

Figure 4 Currents on the load after fault

up of a series of voltage spikes) Other currents on unfaultyphases become phase opposite while the applied voltages onit are half of the line to line voltage with a different sign

Figure 5 shows instead the voltage on an unfaultedphase

Figures 6 and 7 show respectively the same simulationresults when the fault regards both the device and the free-wheeling diode

Voltage is very similar to that of the previous analyzedcase except for a higher number of spikes Currents areinstead quite different being composed of a series of negativepulse due to commutation of the lower transistor Theunfaulted phase voltages are very similar to the previous onesand for this reason are not reported here

4 The Control Strategy for the FaultTolerant Operation

41 The Fault Tolerant Control Arrangement In the case ofloss of an entire leg the only reconnection of the faulted

Advances in Power Electronics 5

0275 028 0285 029 0295 03 0305 031 0315Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119887

(V)

Figure 5 Voltage on an unfaulted phase

031 0315 032 0325 033 0335 034 0345 035Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119887

(V)

Figure 6 Faulty phase voltage after transistor and diode havebroken

Table 1 Synthesis of the postfault reference voltages

Healthy 119880ref Phase 119860 fault Phase 119861 fault Phase 119862 fault119906119860 0 minus119906119862 119906119861

119906119861 119906119862 0 minus119906119860

119906119862 minus119906119861 119906119860 0

phase to DC link middle point does not ensure a correctoperation In particular the current peak amplitude of thefaulted phase results lowers by a factorradic3 In order to obtaina balanced currents system the voltage references used in themodulation process must be changed

In the case of a grid converter its capability to maintaina set of symmetrical voltages is very important for thepower quality in view to limit as possible disturbancespropagation into the grid avoiding oversized apparatuses totheir mitigation

The new modified set of reference voltages in the fault-tolerant mode should then present a minimal inverse com-ponent

033 0335 034 0345 035 0355 036 0365 037Time (s)

minus3

minus2

minus1

0

1

2

3

4

Curr

ents

(A)

Figure 7 Load currents after broken transistor and diodeThe new reference voltages consist of a set of two

sinusoidal signals controlling the healthy legsSuppose now that the signals corresponding phasors are

119880ref1 = 119880119909 exp (1198950)

119880ref2 = 119880119909 exp (minus119895120593) (18)

For the fault cases on phases A B and C respectively theinverse component of this reference system is

119880inv119860 = 0 + 120572119880ref1 + 1205722119880ref2

119880inv119861 = 119880ref1 + 1205720 + 1205722119880ref2

119880inv119862 = 119880ref1 + 120572119880ref2 + 12057220

(19)

By calculating the module of the inverse components itfollows that

1003816100381610038161003816119880inv1003816100381610038161003816 =radic2119880119909

radic1 + cos(120593 plusmn 21205873) (20)

in which the sign ldquo+rdquo is for a fault on phaseA and C while thesign ldquominusrdquo is for a fault on phase B In both cases the minimuminverse factor is reached for120593plusmn21205873 = 120587 that is for120593 = plusmn1205873and it results just |119880inv| = 0

Hence in a fault tolerant converter the new referenceshave equal amplitude and a 60-degree phase displacement

Furthermore the new references can be built followingthe suggestion of Table 1

Therefore the general expression of the reference voltages(119906lowast119896 with 119896 = 119860 119861 119862) for healthy and faulted conditions is

119906lowast119860 = 119906119860ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119862119906119861 minus ℎ119861119906119862)

119906lowast119861 = 119906119861ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119860119906119862 minus ℎ119862119906119860)

119906lowast119862 = 119906119862ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119861119906119860 minus ℎ119860119906119861)

(21)

where 119906119895 is the set of normal symmetrical three-phasereference voltages

6 Advances in Power Electronics

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881A

N(V

)

(a)

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881CN

(V)

(b)

Figure 8 Phase voltages at unfaulted and faulted converter leg

051 052 053 054 055 056 057 058 059Time (s)

minus10

minus8

minus6

minus4

minus2

0

2

4

6

8

10

119894 ABC

(A)

Figure 9 Load current before and after faults

Equation (21) may be also written in vector notation

ulowast = 120582u + radic3u times h (22)

where 120582 = ℎ119860ℎ119861ℎ119862 = det(H119896)The modified reference voltage are very simple to be

implemented on microprocessors and diagnostic signals onthe converters can be used to synthesize the new postfaultreference voltages

In (21) the general term 120582u is the reference for the healthycase while the vectors cross product radic3(u times h) is the newreference in the faulted case The factor radic3 guarantees theidentity of the voltage and current amplitude even after thefault has occurred

Note that the cross product termradic3(utimesh) should be 1205872clockwise rotated if the converter is a grid connected thusmaintaining the synchronization between converter and gridvoltages In this case the reference voltages system expressedin vector form results

ulowast = 120582u + radic3 (u times h) 119890minus119895(1205872) (23)

The first advantage of (23) is a close integration of thediagnostic signals directly in the control for the inverterreconfiguration another advantage is to make the fault andreconfiguration transparent to the main control system In

fact any regulating action of external variables can providea three-phase voltage reference that will be then manipulatedaccording to (23) in order to generate the correct referenceIn other words the only reason for which the control systemcan be affected by the fault is the unavoidable DC link voltageripple (as discussed later) and its effect on the current

42 The Control Simulation Control simulation results areillustrated in the following figures showing how the faultcondition is managed by themodel with themodified controlstrategy in order to guarantee the minimal derating in powerquality

Figure 8 shows the converter phase voltage measured atunfaulted (a) and faulted leg (b) after the faults occurredresulting their first harmonics a symmetrical system evenafter the fault

The voltage waveforms are quite different from those withunfaulted converter condition and the faulted leg voltageexhibits the greatest difference

Figure 9 shows converter currents before and after faultoccurrence with the instantaneous modification of the con-verter references The residual current imbalance after faultis due to the alternating components in the DC-link voltagedepending on the current amplitude and on the outputfrequency In general the voltage oscillation in single DCcapacitors does not affect significantly the entire value of theDC link voltage and the general converter performance

Postfault currents exhibit a phase jump due to reconfig-uration unless this is compensated Figure 10 shows insteadthe effect on load currents with the phase jump correctionintroduced in (23)

The linear region of the converter during the fault is ineach case restricted Linear range is quite important in orderto achieve minimal currents asymmetry

Figure 11 shows a higher load current distortion andunbalance during overmodulation (ie with an amplitudemodulation index higher than 05 in the faulted case)

Figure 12 shows the voltage imbalance on the twoDC linkcapacitors

5 Simulation of a Grid Converter with FaultTolerant Operation

The illustrated simulation was made for a standalone con-verter In the case of a grid converter fed by a DG source

Advances in Power Electronics 7

035 0355 036 0365 037 0375 038minus6

minus4

minus2

0

2

4

6

Time (s)

Phas

e cur

rent

s (A

)

Figure 10 Load currents before and after fault with phase jumpcorrection

138 139 14 141 142 143 144 145 146 147

minus10

minus5

0

5

10

Time (s)

Curr

ents

(A)

Figure 11 Distorted and unbalanced load currents with higherdistortion during faulted condition in overmodulation mode

045 05 055 06 065 07 075 08 085 09140

142

144

146

148

150

152

154

156

158

Time (s)

1198801

and1198802

DC

link

volta

ges (

V)

Figure 12 Voltage unbalance through DC link ca pacitors

the system and the control are more complicated Howeverno modification of the classical control structure of a gridconverter is needed Figure 13 shows the simplified schemeof the control structure for a grid converter control in whichactive and reactive power are managed via current controlloop and DC link voltage loop A complete description ofthe grid converter control system and of some other differentsolutions is given in [28 29]

The control scheme allows active 119875 and reactive power 119876to be managed separately by decoupling DQ channels for thecurrent control so that P depends on 119894119863 and Q depends on119894119876 via previous proper grid synchronization via PLLThe DClink voltage control is also performed

In the example of this section the grid filter is notoptimally designed with the aim to put better in evidencesome aspect of the fault tolerant grid converter behavior

The simulation assumes the occurrence of a fault thefast reconfiguration of the converter and the decrease ofthe active power injected into the grid Subsequently thereactive power transferred to the grid is vanished It is evidentthat despite the active power decrease there is a greaterdistortion of the output current as it is seen in Figures 14and 15 (also with reference to the 119894119863 and 119894119876 components)due to the increased voltage ripple on the DC link Thisoscillation is natural and the control system can only fix itsmean value forced by the set pointThe simulation shows wellas vanishing the delivered reactive power the DC link voltageoscillation decreases with benefit for both the input and thegrid current that exhibit a lower distortion as evident fromFigures 16 17 18 19 and 20

It is worthwhile to remark that for avoiding overmodula-tion the fault tolerant converter has aDC link voltage 25ndash30greater than that of a traditional grid converter

6 Experimental Results

Experimental results were made available in the case of thefault tolerant mode where the reconfiguration makes theconverter operation more safe for a normal laboratory test Itwas not possible to test the converter as a grid-converter oneso the tests on the fault tolerant operation have been made byfeeding an induction motor and registering output voltagesand currents

For the experimental test a customary benchmark basedon an INFRANOR power converter and a dSPACE controlboard has been built and set up

The converter used in the test bench is a commercialfrequency converter whose control board has been replacedby a customary one designed to be driven by the dSPACEcontrol board and converting the TTL gating pulses to theldquoline driverdquo type of the INFRANOR converter (see Figure 21)

In the practical realization of a fault tolerant convertersome issues are mandatory to be taken into account Triacsfor the current path closure may suffer for a 119889V119889119905 not suf-ficient immunity having therefore unwanted switchings Asolution to this problem can be the choice of a different bidi-rectional controllable switch In particular the combinationof power diodes in a bridge configuration with an auxiliary

8 Advances in Power Electronics

From DG sourceThree-phase

network

119875 control

119876lowast

119875lowast

+ minus

PLL

119894119863119894119876

Currentcontroller

and PWM119876 control

PI

PI

PI

Decoupled currentcontroller

DQOABC

Converter

wL119880119902

119880119902

119880119889

119880119889119880119889lowast

119880119902lowastminuswL

119894119876lowast

119894119876lowast

119894119863lowast

119894119863lowast

119894119876

119894119863

119880dclowast

119880dc119880dc[

w

w

Figure 13 The control structure of a grid converter

102 104 106 108 11 112 114 116 118 12

minus10

minus5

0

5

10

119905 (s)

Out

put c

urre

nt (A

)

Figure 14 Current decrease after fault and reconfiguration

IGBT is able to reach bidirectional current circulation (seeFigure 22 for topology details) A fault detection algorithmbased on the elaboration of load current signal has alsobeen implemented An extensive technical literature (see eg[4 5]) exists on fault detection but its discussion here is outof the scopes of this paper

The fed induction motor is a two-pole three-phase squir-rel cage whose nameplate is reported in Table 2

A digital oscilloscope with two differential probes (up toa 25-MHz bandwidth) and 3 accuracy has been used toregister voltage and current waveforms Measurements datawere stored in the computer hosting the dSPACE board withthe help of ldquoOctaverdquo software

Fault emulation have been realized with the help of solidstate relays and connectors being driven from the dSPACEboard and software interface In this way it was possible to

0 05 1 15 2 25 3minus15

minus10

minus5

0

5

10

15

119905 (s)

119894 119863119894 119876

(A)

Figure 15 119894119863 (blue) and 119894119876 (green) current components

test the behavior of the fault-tolerant converter in all possiblecondition without a real disruption of the power devices

Figures 23 24 and 25 shows respectively the measure-ments of voltage on faulty and unfaulty phases and themeasurement of the currents before and after fault andreconfiguration

This final comparison validates the proposed generalmodel of VSI in healthy and faulty mode implementedalgorithm

7 Conclusions

The use of fault-tolerant systems is essential for the optimaldevelopment of electrical power production by renewablesources as well as for the achievement of high reliability

Advances in Power Electronics 9

155 156 157 158 159 16 161 162 163 164

minus5

minus4

minus3

minus2

minus1

0

1

2

3

4

5

119905 (s)

Out

put c

urre

nt (A

)

Figure 16 After fault current zoom

226 227 228 229 23 231 232 233 234minus3

minus2

minus1

0

1

2

119905 (s)

Out

put c

urre

nt (A

)

Figure 17 After fault current with no reactive power

16 165 17 175 18 185

minus200

minus100

0

100

200

Grid

vol

tage

(V)

grid

curr

ent (

A)

minus10

minus5

0

5

10

119905 (s)

Figure 18 Phase voltage (blue dashed) and current (green continu-ous) with and without Q transmission

16 165 17 175 18 185 19 195 2

minus3

minus2

minus1

0

1

2

3

4

119905 (s)

119894 119863119894 119876

(A)

Figure 19 119894119863 and 119894119876 transient after vanishing Q

15 155 16 165 17 175 18 185 19 195 205

06

07

08

09

1

11

12

13

14

15

119905 (s)

Inpu

t cur

rent

(A)

Figure 20 Transient on 1198940 after vanishing Q

Table 2 Test bench induction motor nameplates

Ratings ValuePower 55 kWSpeed 2870 rpmFrequency 50ndash60HzTorque 183NmVoltage 400VCurrent 13 APoles 2

and power quality fundamental for both end users and gridmanager

Fault tolerant converters require intelligent real-timedetection algorithms of incoming failures easy to implementeven on low cost hardware such as microcontrollers orPegasus

In this paper the authors have considered the faulttolerant operation of an inverter for distributed generation

10 Advances in Power Electronics

Figure 21 Picture of the realized test bench

Figure 22 A bidirectional switch realized with diode and IGBT

system seen as an ancillary complementary function inaddiction to the classical ones already developedThe generalinverter model here presented in the paper is suitable anduseful for the simulation of faults and fault-tolerant operationof a VSI The presented model is very helpful to predicttransient phenomena due to faults occurrence Switchingfunction definition has been extended in order to cover thecondition of diode turning on and open fault occurrenceThe introduction of HDBVs and HLBVs allows for theconstruction of a unified model suitable for simulations withequation solver tools This makes the simulations affordableand at the same time fast in their operation

The implementation algorithm is very suitable in largecontext as grid connected converter for DG because it istransparent to the action of the main power control andsynchronization

Numerical simulations presented in the paper have con-sidered both a standalone and a grid converter In order toguarantee minimal power quality degradation the followingconsiderations apply in the converter control

(i) over modulation must be avoided(ii) for this reason both a reduction of the transmitted

active power and vanishing the reactive power aremandatory

(iii) a 25ndash30 greater DC link voltage with respect totraditional value must be chosen

The control has been also verified with experimental resultsin the case of reconfigurable operation Comparison of

004 006 008 01 012 014 016 018 02Time (s)

minus250

minus200

minus150

minus100

minus50

0

50

100

150

200

250

119881119886

(V)

Figure 23 Measurement of faulty phase voltage before and after thefault

005 01 015Time (s)

minus300

minus200

minus100

0

100

200119881119887

(V)

Figure 24 Measurement of unfaulty phase voltage before and afterthe fault

002 004 006 008 01 012 014 016 018 02Time (s)

minus10

minus5

0

5

10

119894 ABC

(A)

Figure 25Measurement of phase currents before and after the fault

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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DistributedSensor Networks

International Journal of

Advances in Power Electronics 5

0275 028 0285 029 0295 03 0305 031 0315Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119887

(V)

Figure 5 Voltage on an unfaulted phase

031 0315 032 0325 033 0335 034 0345 035Time (s)

minus200

minus150

minus100

minus50

0

50

100

150

200

119881119887

(V)

Figure 6 Faulty phase voltage after transistor and diode havebroken

Table 1 Synthesis of the postfault reference voltages

Healthy 119880ref Phase 119860 fault Phase 119861 fault Phase 119862 fault119906119860 0 minus119906119862 119906119861

119906119861 119906119862 0 minus119906119860

119906119862 minus119906119861 119906119860 0

phase to DC link middle point does not ensure a correctoperation In particular the current peak amplitude of thefaulted phase results lowers by a factorradic3 In order to obtaina balanced currents system the voltage references used in themodulation process must be changed

In the case of a grid converter its capability to maintaina set of symmetrical voltages is very important for thepower quality in view to limit as possible disturbancespropagation into the grid avoiding oversized apparatuses totheir mitigation

The new modified set of reference voltages in the fault-tolerant mode should then present a minimal inverse com-ponent

033 0335 034 0345 035 0355 036 0365 037Time (s)

minus3

minus2

minus1

0

1

2

3

4

Curr

ents

(A)

Figure 7 Load currents after broken transistor and diodeThe new reference voltages consist of a set of two

sinusoidal signals controlling the healthy legsSuppose now that the signals corresponding phasors are

119880ref1 = 119880119909 exp (1198950)

119880ref2 = 119880119909 exp (minus119895120593) (18)

For the fault cases on phases A B and C respectively theinverse component of this reference system is

119880inv119860 = 0 + 120572119880ref1 + 1205722119880ref2

119880inv119861 = 119880ref1 + 1205720 + 1205722119880ref2

119880inv119862 = 119880ref1 + 120572119880ref2 + 12057220

(19)

By calculating the module of the inverse components itfollows that

1003816100381610038161003816119880inv1003816100381610038161003816 =radic2119880119909

radic1 + cos(120593 plusmn 21205873) (20)

in which the sign ldquo+rdquo is for a fault on phaseA and C while thesign ldquominusrdquo is for a fault on phase B In both cases the minimuminverse factor is reached for120593plusmn21205873 = 120587 that is for120593 = plusmn1205873and it results just |119880inv| = 0

Hence in a fault tolerant converter the new referenceshave equal amplitude and a 60-degree phase displacement

Furthermore the new references can be built followingthe suggestion of Table 1

Therefore the general expression of the reference voltages(119906lowast119896 with 119896 = 119860 119861 119862) for healthy and faulted conditions is

119906lowast119860 = 119906119860ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119862119906119861 minus ℎ119861119906119862)

119906lowast119861 = 119906119861ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119860119906119862 minus ℎ119862119906119860)

119906lowast119862 = 119906119862ℎ119860ℎ119861ℎ119862 +

radic3 (ℎ119861119906119860 minus ℎ119860119906119861)

(21)

where 119906119895 is the set of normal symmetrical three-phasereference voltages

6 Advances in Power Electronics

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881A

N(V

)

(a)

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881CN

(V)

(b)

Figure 8 Phase voltages at unfaulted and faulted converter leg

051 052 053 054 055 056 057 058 059Time (s)

minus10

minus8

minus6

minus4

minus2

0

2

4

6

8

10

119894 ABC

(A)

Figure 9 Load current before and after faults

Equation (21) may be also written in vector notation

ulowast = 120582u + radic3u times h (22)

where 120582 = ℎ119860ℎ119861ℎ119862 = det(H119896)The modified reference voltage are very simple to be

implemented on microprocessors and diagnostic signals onthe converters can be used to synthesize the new postfaultreference voltages

In (21) the general term 120582u is the reference for the healthycase while the vectors cross product radic3(u times h) is the newreference in the faulted case The factor radic3 guarantees theidentity of the voltage and current amplitude even after thefault has occurred

Note that the cross product termradic3(utimesh) should be 1205872clockwise rotated if the converter is a grid connected thusmaintaining the synchronization between converter and gridvoltages In this case the reference voltages system expressedin vector form results

ulowast = 120582u + radic3 (u times h) 119890minus119895(1205872) (23)

The first advantage of (23) is a close integration of thediagnostic signals directly in the control for the inverterreconfiguration another advantage is to make the fault andreconfiguration transparent to the main control system In

fact any regulating action of external variables can providea three-phase voltage reference that will be then manipulatedaccording to (23) in order to generate the correct referenceIn other words the only reason for which the control systemcan be affected by the fault is the unavoidable DC link voltageripple (as discussed later) and its effect on the current

42 The Control Simulation Control simulation results areillustrated in the following figures showing how the faultcondition is managed by themodel with themodified controlstrategy in order to guarantee the minimal derating in powerquality

Figure 8 shows the converter phase voltage measured atunfaulted (a) and faulted leg (b) after the faults occurredresulting their first harmonics a symmetrical system evenafter the fault

The voltage waveforms are quite different from those withunfaulted converter condition and the faulted leg voltageexhibits the greatest difference

Figure 9 shows converter currents before and after faultoccurrence with the instantaneous modification of the con-verter references The residual current imbalance after faultis due to the alternating components in the DC-link voltagedepending on the current amplitude and on the outputfrequency In general the voltage oscillation in single DCcapacitors does not affect significantly the entire value of theDC link voltage and the general converter performance

Postfault currents exhibit a phase jump due to reconfig-uration unless this is compensated Figure 10 shows insteadthe effect on load currents with the phase jump correctionintroduced in (23)

The linear region of the converter during the fault is ineach case restricted Linear range is quite important in orderto achieve minimal currents asymmetry

Figure 11 shows a higher load current distortion andunbalance during overmodulation (ie with an amplitudemodulation index higher than 05 in the faulted case)

Figure 12 shows the voltage imbalance on the twoDC linkcapacitors

5 Simulation of a Grid Converter with FaultTolerant Operation

The illustrated simulation was made for a standalone con-verter In the case of a grid converter fed by a DG source

Advances in Power Electronics 7

035 0355 036 0365 037 0375 038minus6

minus4

minus2

0

2

4

6

Time (s)

Phas

e cur

rent

s (A

)

Figure 10 Load currents before and after fault with phase jumpcorrection

138 139 14 141 142 143 144 145 146 147

minus10

minus5

0

5

10

Time (s)

Curr

ents

(A)

Figure 11 Distorted and unbalanced load currents with higherdistortion during faulted condition in overmodulation mode

045 05 055 06 065 07 075 08 085 09140

142

144

146

148

150

152

154

156

158

Time (s)

1198801

and1198802

DC

link

volta

ges (

V)

Figure 12 Voltage unbalance through DC link ca pacitors

the system and the control are more complicated Howeverno modification of the classical control structure of a gridconverter is needed Figure 13 shows the simplified schemeof the control structure for a grid converter control in whichactive and reactive power are managed via current controlloop and DC link voltage loop A complete description ofthe grid converter control system and of some other differentsolutions is given in [28 29]

The control scheme allows active 119875 and reactive power 119876to be managed separately by decoupling DQ channels for thecurrent control so that P depends on 119894119863 and Q depends on119894119876 via previous proper grid synchronization via PLLThe DClink voltage control is also performed

In the example of this section the grid filter is notoptimally designed with the aim to put better in evidencesome aspect of the fault tolerant grid converter behavior

The simulation assumes the occurrence of a fault thefast reconfiguration of the converter and the decrease ofthe active power injected into the grid Subsequently thereactive power transferred to the grid is vanished It is evidentthat despite the active power decrease there is a greaterdistortion of the output current as it is seen in Figures 14and 15 (also with reference to the 119894119863 and 119894119876 components)due to the increased voltage ripple on the DC link Thisoscillation is natural and the control system can only fix itsmean value forced by the set pointThe simulation shows wellas vanishing the delivered reactive power the DC link voltageoscillation decreases with benefit for both the input and thegrid current that exhibit a lower distortion as evident fromFigures 16 17 18 19 and 20

It is worthwhile to remark that for avoiding overmodula-tion the fault tolerant converter has aDC link voltage 25ndash30greater than that of a traditional grid converter

6 Experimental Results

Experimental results were made available in the case of thefault tolerant mode where the reconfiguration makes theconverter operation more safe for a normal laboratory test Itwas not possible to test the converter as a grid-converter oneso the tests on the fault tolerant operation have been made byfeeding an induction motor and registering output voltagesand currents

For the experimental test a customary benchmark basedon an INFRANOR power converter and a dSPACE controlboard has been built and set up

The converter used in the test bench is a commercialfrequency converter whose control board has been replacedby a customary one designed to be driven by the dSPACEcontrol board and converting the TTL gating pulses to theldquoline driverdquo type of the INFRANOR converter (see Figure 21)

In the practical realization of a fault tolerant convertersome issues are mandatory to be taken into account Triacsfor the current path closure may suffer for a 119889V119889119905 not suf-ficient immunity having therefore unwanted switchings Asolution to this problem can be the choice of a different bidi-rectional controllable switch In particular the combinationof power diodes in a bridge configuration with an auxiliary

8 Advances in Power Electronics

From DG sourceThree-phase

network

119875 control

119876lowast

119875lowast

+ minus

PLL

119894119863119894119876

Currentcontroller

and PWM119876 control

PI

PI

PI

Decoupled currentcontroller

DQOABC

Converter

wL119880119902

119880119902

119880119889

119880119889119880119889lowast

119880119902lowastminuswL

119894119876lowast

119894119876lowast

119894119863lowast

119894119863lowast

119894119876

119894119863

119880dclowast

119880dc119880dc[

w

w

Figure 13 The control structure of a grid converter

102 104 106 108 11 112 114 116 118 12

minus10

minus5

0

5

10

119905 (s)

Out

put c

urre

nt (A

)

Figure 14 Current decrease after fault and reconfiguration

IGBT is able to reach bidirectional current circulation (seeFigure 22 for topology details) A fault detection algorithmbased on the elaboration of load current signal has alsobeen implemented An extensive technical literature (see eg[4 5]) exists on fault detection but its discussion here is outof the scopes of this paper

The fed induction motor is a two-pole three-phase squir-rel cage whose nameplate is reported in Table 2

A digital oscilloscope with two differential probes (up toa 25-MHz bandwidth) and 3 accuracy has been used toregister voltage and current waveforms Measurements datawere stored in the computer hosting the dSPACE board withthe help of ldquoOctaverdquo software

Fault emulation have been realized with the help of solidstate relays and connectors being driven from the dSPACEboard and software interface In this way it was possible to

0 05 1 15 2 25 3minus15

minus10

minus5

0

5

10

15

119905 (s)

119894 119863119894 119876

(A)

Figure 15 119894119863 (blue) and 119894119876 (green) current components

test the behavior of the fault-tolerant converter in all possiblecondition without a real disruption of the power devices

Figures 23 24 and 25 shows respectively the measure-ments of voltage on faulty and unfaulty phases and themeasurement of the currents before and after fault andreconfiguration

This final comparison validates the proposed generalmodel of VSI in healthy and faulty mode implementedalgorithm

7 Conclusions

The use of fault-tolerant systems is essential for the optimaldevelopment of electrical power production by renewablesources as well as for the achievement of high reliability

Advances in Power Electronics 9

155 156 157 158 159 16 161 162 163 164

minus5

minus4

minus3

minus2

minus1

0

1

2

3

4

5

119905 (s)

Out

put c

urre

nt (A

)

Figure 16 After fault current zoom

226 227 228 229 23 231 232 233 234minus3

minus2

minus1

0

1

2

119905 (s)

Out

put c

urre

nt (A

)

Figure 17 After fault current with no reactive power

16 165 17 175 18 185

minus200

minus100

0

100

200

Grid

vol

tage

(V)

grid

curr

ent (

A)

minus10

minus5

0

5

10

119905 (s)

Figure 18 Phase voltage (blue dashed) and current (green continu-ous) with and without Q transmission

16 165 17 175 18 185 19 195 2

minus3

minus2

minus1

0

1

2

3

4

119905 (s)

119894 119863119894 119876

(A)

Figure 19 119894119863 and 119894119876 transient after vanishing Q

15 155 16 165 17 175 18 185 19 195 205

06

07

08

09

1

11

12

13

14

15

119905 (s)

Inpu

t cur

rent

(A)

Figure 20 Transient on 1198940 after vanishing Q

Table 2 Test bench induction motor nameplates

Ratings ValuePower 55 kWSpeed 2870 rpmFrequency 50ndash60HzTorque 183NmVoltage 400VCurrent 13 APoles 2

and power quality fundamental for both end users and gridmanager

Fault tolerant converters require intelligent real-timedetection algorithms of incoming failures easy to implementeven on low cost hardware such as microcontrollers orPegasus

In this paper the authors have considered the faulttolerant operation of an inverter for distributed generation

10 Advances in Power Electronics

Figure 21 Picture of the realized test bench

Figure 22 A bidirectional switch realized with diode and IGBT

system seen as an ancillary complementary function inaddiction to the classical ones already developedThe generalinverter model here presented in the paper is suitable anduseful for the simulation of faults and fault-tolerant operationof a VSI The presented model is very helpful to predicttransient phenomena due to faults occurrence Switchingfunction definition has been extended in order to cover thecondition of diode turning on and open fault occurrenceThe introduction of HDBVs and HLBVs allows for theconstruction of a unified model suitable for simulations withequation solver tools This makes the simulations affordableand at the same time fast in their operation

The implementation algorithm is very suitable in largecontext as grid connected converter for DG because it istransparent to the action of the main power control andsynchronization

Numerical simulations presented in the paper have con-sidered both a standalone and a grid converter In order toguarantee minimal power quality degradation the followingconsiderations apply in the converter control

(i) over modulation must be avoided(ii) for this reason both a reduction of the transmitted

active power and vanishing the reactive power aremandatory

(iii) a 25ndash30 greater DC link voltage with respect totraditional value must be chosen

The control has been also verified with experimental resultsin the case of reconfigurable operation Comparison of

004 006 008 01 012 014 016 018 02Time (s)

minus250

minus200

minus150

minus100

minus50

0

50

100

150

200

250

119881119886

(V)

Figure 23 Measurement of faulty phase voltage before and after thefault

005 01 015Time (s)

minus300

minus200

minus100

0

100

200119881119887

(V)

Figure 24 Measurement of unfaulty phase voltage before and afterthe fault

002 004 006 008 01 012 014 016 018 02Time (s)

minus10

minus5

0

5

10

119894 ABC

(A)

Figure 25Measurement of phase currents before and after the fault

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

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Active and Passive Electronic Components

Control Scienceand Engineering

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Shock and Vibration

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Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

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Electrical and Computer Engineering

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Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

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Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

6 Advances in Power Electronics

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881A

N(V

)

(a)

05 051 052 053 054 055 056 057 058 059 06Time (s)

minus300minus200minus100

0100200300

119881CN

(V)

(b)

Figure 8 Phase voltages at unfaulted and faulted converter leg

051 052 053 054 055 056 057 058 059Time (s)

minus10

minus8

minus6

minus4

minus2

0

2

4

6

8

10

119894 ABC

(A)

Figure 9 Load current before and after faults

Equation (21) may be also written in vector notation

ulowast = 120582u + radic3u times h (22)

where 120582 = ℎ119860ℎ119861ℎ119862 = det(H119896)The modified reference voltage are very simple to be

implemented on microprocessors and diagnostic signals onthe converters can be used to synthesize the new postfaultreference voltages

In (21) the general term 120582u is the reference for the healthycase while the vectors cross product radic3(u times h) is the newreference in the faulted case The factor radic3 guarantees theidentity of the voltage and current amplitude even after thefault has occurred

Note that the cross product termradic3(utimesh) should be 1205872clockwise rotated if the converter is a grid connected thusmaintaining the synchronization between converter and gridvoltages In this case the reference voltages system expressedin vector form results

ulowast = 120582u + radic3 (u times h) 119890minus119895(1205872) (23)

The first advantage of (23) is a close integration of thediagnostic signals directly in the control for the inverterreconfiguration another advantage is to make the fault andreconfiguration transparent to the main control system In

fact any regulating action of external variables can providea three-phase voltage reference that will be then manipulatedaccording to (23) in order to generate the correct referenceIn other words the only reason for which the control systemcan be affected by the fault is the unavoidable DC link voltageripple (as discussed later) and its effect on the current

42 The Control Simulation Control simulation results areillustrated in the following figures showing how the faultcondition is managed by themodel with themodified controlstrategy in order to guarantee the minimal derating in powerquality

Figure 8 shows the converter phase voltage measured atunfaulted (a) and faulted leg (b) after the faults occurredresulting their first harmonics a symmetrical system evenafter the fault

The voltage waveforms are quite different from those withunfaulted converter condition and the faulted leg voltageexhibits the greatest difference

Figure 9 shows converter currents before and after faultoccurrence with the instantaneous modification of the con-verter references The residual current imbalance after faultis due to the alternating components in the DC-link voltagedepending on the current amplitude and on the outputfrequency In general the voltage oscillation in single DCcapacitors does not affect significantly the entire value of theDC link voltage and the general converter performance

Postfault currents exhibit a phase jump due to reconfig-uration unless this is compensated Figure 10 shows insteadthe effect on load currents with the phase jump correctionintroduced in (23)

The linear region of the converter during the fault is ineach case restricted Linear range is quite important in orderto achieve minimal currents asymmetry

Figure 11 shows a higher load current distortion andunbalance during overmodulation (ie with an amplitudemodulation index higher than 05 in the faulted case)

Figure 12 shows the voltage imbalance on the twoDC linkcapacitors

5 Simulation of a Grid Converter with FaultTolerant Operation

The illustrated simulation was made for a standalone con-verter In the case of a grid converter fed by a DG source

Advances in Power Electronics 7

035 0355 036 0365 037 0375 038minus6

minus4

minus2

0

2

4

6

Time (s)

Phas

e cur

rent

s (A

)

Figure 10 Load currents before and after fault with phase jumpcorrection

138 139 14 141 142 143 144 145 146 147

minus10

minus5

0

5

10

Time (s)

Curr

ents

(A)

Figure 11 Distorted and unbalanced load currents with higherdistortion during faulted condition in overmodulation mode

045 05 055 06 065 07 075 08 085 09140

142

144

146

148

150

152

154

156

158

Time (s)

1198801

and1198802

DC

link

volta

ges (

V)

Figure 12 Voltage unbalance through DC link ca pacitors

the system and the control are more complicated Howeverno modification of the classical control structure of a gridconverter is needed Figure 13 shows the simplified schemeof the control structure for a grid converter control in whichactive and reactive power are managed via current controlloop and DC link voltage loop A complete description ofthe grid converter control system and of some other differentsolutions is given in [28 29]

The control scheme allows active 119875 and reactive power 119876to be managed separately by decoupling DQ channels for thecurrent control so that P depends on 119894119863 and Q depends on119894119876 via previous proper grid synchronization via PLLThe DClink voltage control is also performed

In the example of this section the grid filter is notoptimally designed with the aim to put better in evidencesome aspect of the fault tolerant grid converter behavior

The simulation assumes the occurrence of a fault thefast reconfiguration of the converter and the decrease ofthe active power injected into the grid Subsequently thereactive power transferred to the grid is vanished It is evidentthat despite the active power decrease there is a greaterdistortion of the output current as it is seen in Figures 14and 15 (also with reference to the 119894119863 and 119894119876 components)due to the increased voltage ripple on the DC link Thisoscillation is natural and the control system can only fix itsmean value forced by the set pointThe simulation shows wellas vanishing the delivered reactive power the DC link voltageoscillation decreases with benefit for both the input and thegrid current that exhibit a lower distortion as evident fromFigures 16 17 18 19 and 20

It is worthwhile to remark that for avoiding overmodula-tion the fault tolerant converter has aDC link voltage 25ndash30greater than that of a traditional grid converter

6 Experimental Results

Experimental results were made available in the case of thefault tolerant mode where the reconfiguration makes theconverter operation more safe for a normal laboratory test Itwas not possible to test the converter as a grid-converter oneso the tests on the fault tolerant operation have been made byfeeding an induction motor and registering output voltagesand currents

For the experimental test a customary benchmark basedon an INFRANOR power converter and a dSPACE controlboard has been built and set up

The converter used in the test bench is a commercialfrequency converter whose control board has been replacedby a customary one designed to be driven by the dSPACEcontrol board and converting the TTL gating pulses to theldquoline driverdquo type of the INFRANOR converter (see Figure 21)

In the practical realization of a fault tolerant convertersome issues are mandatory to be taken into account Triacsfor the current path closure may suffer for a 119889V119889119905 not suf-ficient immunity having therefore unwanted switchings Asolution to this problem can be the choice of a different bidi-rectional controllable switch In particular the combinationof power diodes in a bridge configuration with an auxiliary

8 Advances in Power Electronics

From DG sourceThree-phase

network

119875 control

119876lowast

119875lowast

+ minus

PLL

119894119863119894119876

Currentcontroller

and PWM119876 control

PI

PI

PI

Decoupled currentcontroller

DQOABC

Converter

wL119880119902

119880119902

119880119889

119880119889119880119889lowast

119880119902lowastminuswL

119894119876lowast

119894119876lowast

119894119863lowast

119894119863lowast

119894119876

119894119863

119880dclowast

119880dc119880dc[

w

w

Figure 13 The control structure of a grid converter

102 104 106 108 11 112 114 116 118 12

minus10

minus5

0

5

10

119905 (s)

Out

put c

urre

nt (A

)

Figure 14 Current decrease after fault and reconfiguration

IGBT is able to reach bidirectional current circulation (seeFigure 22 for topology details) A fault detection algorithmbased on the elaboration of load current signal has alsobeen implemented An extensive technical literature (see eg[4 5]) exists on fault detection but its discussion here is outof the scopes of this paper

The fed induction motor is a two-pole three-phase squir-rel cage whose nameplate is reported in Table 2

A digital oscilloscope with two differential probes (up toa 25-MHz bandwidth) and 3 accuracy has been used toregister voltage and current waveforms Measurements datawere stored in the computer hosting the dSPACE board withthe help of ldquoOctaverdquo software

Fault emulation have been realized with the help of solidstate relays and connectors being driven from the dSPACEboard and software interface In this way it was possible to

0 05 1 15 2 25 3minus15

minus10

minus5

0

5

10

15

119905 (s)

119894 119863119894 119876

(A)

Figure 15 119894119863 (blue) and 119894119876 (green) current components

test the behavior of the fault-tolerant converter in all possiblecondition without a real disruption of the power devices

Figures 23 24 and 25 shows respectively the measure-ments of voltage on faulty and unfaulty phases and themeasurement of the currents before and after fault andreconfiguration

This final comparison validates the proposed generalmodel of VSI in healthy and faulty mode implementedalgorithm

7 Conclusions

The use of fault-tolerant systems is essential for the optimaldevelopment of electrical power production by renewablesources as well as for the achievement of high reliability

Advances in Power Electronics 9

155 156 157 158 159 16 161 162 163 164

minus5

minus4

minus3

minus2

minus1

0

1

2

3

4

5

119905 (s)

Out

put c

urre

nt (A

)

Figure 16 After fault current zoom

226 227 228 229 23 231 232 233 234minus3

minus2

minus1

0

1

2

119905 (s)

Out

put c

urre

nt (A

)

Figure 17 After fault current with no reactive power

16 165 17 175 18 185

minus200

minus100

0

100

200

Grid

vol

tage

(V)

grid

curr

ent (

A)

minus10

minus5

0

5

10

119905 (s)

Figure 18 Phase voltage (blue dashed) and current (green continu-ous) with and without Q transmission

16 165 17 175 18 185 19 195 2

minus3

minus2

minus1

0

1

2

3

4

119905 (s)

119894 119863119894 119876

(A)

Figure 19 119894119863 and 119894119876 transient after vanishing Q

15 155 16 165 17 175 18 185 19 195 205

06

07

08

09

1

11

12

13

14

15

119905 (s)

Inpu

t cur

rent

(A)

Figure 20 Transient on 1198940 after vanishing Q

Table 2 Test bench induction motor nameplates

Ratings ValuePower 55 kWSpeed 2870 rpmFrequency 50ndash60HzTorque 183NmVoltage 400VCurrent 13 APoles 2

and power quality fundamental for both end users and gridmanager

Fault tolerant converters require intelligent real-timedetection algorithms of incoming failures easy to implementeven on low cost hardware such as microcontrollers orPegasus

In this paper the authors have considered the faulttolerant operation of an inverter for distributed generation

10 Advances in Power Electronics

Figure 21 Picture of the realized test bench

Figure 22 A bidirectional switch realized with diode and IGBT

system seen as an ancillary complementary function inaddiction to the classical ones already developedThe generalinverter model here presented in the paper is suitable anduseful for the simulation of faults and fault-tolerant operationof a VSI The presented model is very helpful to predicttransient phenomena due to faults occurrence Switchingfunction definition has been extended in order to cover thecondition of diode turning on and open fault occurrenceThe introduction of HDBVs and HLBVs allows for theconstruction of a unified model suitable for simulations withequation solver tools This makes the simulations affordableand at the same time fast in their operation

The implementation algorithm is very suitable in largecontext as grid connected converter for DG because it istransparent to the action of the main power control andsynchronization

Numerical simulations presented in the paper have con-sidered both a standalone and a grid converter In order toguarantee minimal power quality degradation the followingconsiderations apply in the converter control

(i) over modulation must be avoided(ii) for this reason both a reduction of the transmitted

active power and vanishing the reactive power aremandatory

(iii) a 25ndash30 greater DC link voltage with respect totraditional value must be chosen

The control has been also verified with experimental resultsin the case of reconfigurable operation Comparison of

004 006 008 01 012 014 016 018 02Time (s)

minus250

minus200

minus150

minus100

minus50

0

50

100

150

200

250

119881119886

(V)

Figure 23 Measurement of faulty phase voltage before and after thefault

005 01 015Time (s)

minus300

minus200

minus100

0

100

200119881119887

(V)

Figure 24 Measurement of unfaulty phase voltage before and afterthe fault

002 004 006 008 01 012 014 016 018 02Time (s)

minus10

minus5

0

5

10

119894 ABC

(A)

Figure 25Measurement of phase currents before and after the fault

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Advances in Power Electronics 7

035 0355 036 0365 037 0375 038minus6

minus4

minus2

0

2

4

6

Time (s)

Phas

e cur

rent

s (A

)

Figure 10 Load currents before and after fault with phase jumpcorrection

138 139 14 141 142 143 144 145 146 147

minus10

minus5

0

5

10

Time (s)

Curr

ents

(A)

Figure 11 Distorted and unbalanced load currents with higherdistortion during faulted condition in overmodulation mode

045 05 055 06 065 07 075 08 085 09140

142

144

146

148

150

152

154

156

158

Time (s)

1198801

and1198802

DC

link

volta

ges (

V)

Figure 12 Voltage unbalance through DC link ca pacitors

the system and the control are more complicated Howeverno modification of the classical control structure of a gridconverter is needed Figure 13 shows the simplified schemeof the control structure for a grid converter control in whichactive and reactive power are managed via current controlloop and DC link voltage loop A complete description ofthe grid converter control system and of some other differentsolutions is given in [28 29]

The control scheme allows active 119875 and reactive power 119876to be managed separately by decoupling DQ channels for thecurrent control so that P depends on 119894119863 and Q depends on119894119876 via previous proper grid synchronization via PLLThe DClink voltage control is also performed

In the example of this section the grid filter is notoptimally designed with the aim to put better in evidencesome aspect of the fault tolerant grid converter behavior

The simulation assumes the occurrence of a fault thefast reconfiguration of the converter and the decrease ofthe active power injected into the grid Subsequently thereactive power transferred to the grid is vanished It is evidentthat despite the active power decrease there is a greaterdistortion of the output current as it is seen in Figures 14and 15 (also with reference to the 119894119863 and 119894119876 components)due to the increased voltage ripple on the DC link Thisoscillation is natural and the control system can only fix itsmean value forced by the set pointThe simulation shows wellas vanishing the delivered reactive power the DC link voltageoscillation decreases with benefit for both the input and thegrid current that exhibit a lower distortion as evident fromFigures 16 17 18 19 and 20

It is worthwhile to remark that for avoiding overmodula-tion the fault tolerant converter has aDC link voltage 25ndash30greater than that of a traditional grid converter

6 Experimental Results

Experimental results were made available in the case of thefault tolerant mode where the reconfiguration makes theconverter operation more safe for a normal laboratory test Itwas not possible to test the converter as a grid-converter oneso the tests on the fault tolerant operation have been made byfeeding an induction motor and registering output voltagesand currents

For the experimental test a customary benchmark basedon an INFRANOR power converter and a dSPACE controlboard has been built and set up

The converter used in the test bench is a commercialfrequency converter whose control board has been replacedby a customary one designed to be driven by the dSPACEcontrol board and converting the TTL gating pulses to theldquoline driverdquo type of the INFRANOR converter (see Figure 21)

In the practical realization of a fault tolerant convertersome issues are mandatory to be taken into account Triacsfor the current path closure may suffer for a 119889V119889119905 not suf-ficient immunity having therefore unwanted switchings Asolution to this problem can be the choice of a different bidi-rectional controllable switch In particular the combinationof power diodes in a bridge configuration with an auxiliary

8 Advances in Power Electronics

From DG sourceThree-phase

network

119875 control

119876lowast

119875lowast

+ minus

PLL

119894119863119894119876

Currentcontroller

and PWM119876 control

PI

PI

PI

Decoupled currentcontroller

DQOABC

Converter

wL119880119902

119880119902

119880119889

119880119889119880119889lowast

119880119902lowastminuswL

119894119876lowast

119894119876lowast

119894119863lowast

119894119863lowast

119894119876

119894119863

119880dclowast

119880dc119880dc[

w

w

Figure 13 The control structure of a grid converter

102 104 106 108 11 112 114 116 118 12

minus10

minus5

0

5

10

119905 (s)

Out

put c

urre

nt (A

)

Figure 14 Current decrease after fault and reconfiguration

IGBT is able to reach bidirectional current circulation (seeFigure 22 for topology details) A fault detection algorithmbased on the elaboration of load current signal has alsobeen implemented An extensive technical literature (see eg[4 5]) exists on fault detection but its discussion here is outof the scopes of this paper

The fed induction motor is a two-pole three-phase squir-rel cage whose nameplate is reported in Table 2

A digital oscilloscope with two differential probes (up toa 25-MHz bandwidth) and 3 accuracy has been used toregister voltage and current waveforms Measurements datawere stored in the computer hosting the dSPACE board withthe help of ldquoOctaverdquo software

Fault emulation have been realized with the help of solidstate relays and connectors being driven from the dSPACEboard and software interface In this way it was possible to

0 05 1 15 2 25 3minus15

minus10

minus5

0

5

10

15

119905 (s)

119894 119863119894 119876

(A)

Figure 15 119894119863 (blue) and 119894119876 (green) current components

test the behavior of the fault-tolerant converter in all possiblecondition without a real disruption of the power devices

Figures 23 24 and 25 shows respectively the measure-ments of voltage on faulty and unfaulty phases and themeasurement of the currents before and after fault andreconfiguration

This final comparison validates the proposed generalmodel of VSI in healthy and faulty mode implementedalgorithm

7 Conclusions

The use of fault-tolerant systems is essential for the optimaldevelopment of electrical power production by renewablesources as well as for the achievement of high reliability

Advances in Power Electronics 9

155 156 157 158 159 16 161 162 163 164

minus5

minus4

minus3

minus2

minus1

0

1

2

3

4

5

119905 (s)

Out

put c

urre

nt (A

)

Figure 16 After fault current zoom

226 227 228 229 23 231 232 233 234minus3

minus2

minus1

0

1

2

119905 (s)

Out

put c

urre

nt (A

)

Figure 17 After fault current with no reactive power

16 165 17 175 18 185

minus200

minus100

0

100

200

Grid

vol

tage

(V)

grid

curr

ent (

A)

minus10

minus5

0

5

10

119905 (s)

Figure 18 Phase voltage (blue dashed) and current (green continu-ous) with and without Q transmission

16 165 17 175 18 185 19 195 2

minus3

minus2

minus1

0

1

2

3

4

119905 (s)

119894 119863119894 119876

(A)

Figure 19 119894119863 and 119894119876 transient after vanishing Q

15 155 16 165 17 175 18 185 19 195 205

06

07

08

09

1

11

12

13

14

15

119905 (s)

Inpu

t cur

rent

(A)

Figure 20 Transient on 1198940 after vanishing Q

Table 2 Test bench induction motor nameplates

Ratings ValuePower 55 kWSpeed 2870 rpmFrequency 50ndash60HzTorque 183NmVoltage 400VCurrent 13 APoles 2

and power quality fundamental for both end users and gridmanager

Fault tolerant converters require intelligent real-timedetection algorithms of incoming failures easy to implementeven on low cost hardware such as microcontrollers orPegasus

In this paper the authors have considered the faulttolerant operation of an inverter for distributed generation

10 Advances in Power Electronics

Figure 21 Picture of the realized test bench

Figure 22 A bidirectional switch realized with diode and IGBT

system seen as an ancillary complementary function inaddiction to the classical ones already developedThe generalinverter model here presented in the paper is suitable anduseful for the simulation of faults and fault-tolerant operationof a VSI The presented model is very helpful to predicttransient phenomena due to faults occurrence Switchingfunction definition has been extended in order to cover thecondition of diode turning on and open fault occurrenceThe introduction of HDBVs and HLBVs allows for theconstruction of a unified model suitable for simulations withequation solver tools This makes the simulations affordableand at the same time fast in their operation

The implementation algorithm is very suitable in largecontext as grid connected converter for DG because it istransparent to the action of the main power control andsynchronization

Numerical simulations presented in the paper have con-sidered both a standalone and a grid converter In order toguarantee minimal power quality degradation the followingconsiderations apply in the converter control

(i) over modulation must be avoided(ii) for this reason both a reduction of the transmitted

active power and vanishing the reactive power aremandatory

(iii) a 25ndash30 greater DC link voltage with respect totraditional value must be chosen

The control has been also verified with experimental resultsin the case of reconfigurable operation Comparison of

004 006 008 01 012 014 016 018 02Time (s)

minus250

minus200

minus150

minus100

minus50

0

50

100

150

200

250

119881119886

(V)

Figure 23 Measurement of faulty phase voltage before and after thefault

005 01 015Time (s)

minus300

minus200

minus100

0

100

200119881119887

(V)

Figure 24 Measurement of unfaulty phase voltage before and afterthe fault

002 004 006 008 01 012 014 016 018 02Time (s)

minus10

minus5

0

5

10

119894 ABC

(A)

Figure 25Measurement of phase currents before and after the fault

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

8 Advances in Power Electronics

From DG sourceThree-phase

network

119875 control

119876lowast

119875lowast

+ minus

PLL

119894119863119894119876

Currentcontroller

and PWM119876 control

PI

PI

PI

Decoupled currentcontroller

DQOABC

Converter

wL119880119902

119880119902

119880119889

119880119889119880119889lowast

119880119902lowastminuswL

119894119876lowast

119894119876lowast

119894119863lowast

119894119863lowast

119894119876

119894119863

119880dclowast

119880dc119880dc[

w

w

Figure 13 The control structure of a grid converter

102 104 106 108 11 112 114 116 118 12

minus10

minus5

0

5

10

119905 (s)

Out

put c

urre

nt (A

)

Figure 14 Current decrease after fault and reconfiguration

IGBT is able to reach bidirectional current circulation (seeFigure 22 for topology details) A fault detection algorithmbased on the elaboration of load current signal has alsobeen implemented An extensive technical literature (see eg[4 5]) exists on fault detection but its discussion here is outof the scopes of this paper

The fed induction motor is a two-pole three-phase squir-rel cage whose nameplate is reported in Table 2

A digital oscilloscope with two differential probes (up toa 25-MHz bandwidth) and 3 accuracy has been used toregister voltage and current waveforms Measurements datawere stored in the computer hosting the dSPACE board withthe help of ldquoOctaverdquo software

Fault emulation have been realized with the help of solidstate relays and connectors being driven from the dSPACEboard and software interface In this way it was possible to

0 05 1 15 2 25 3minus15

minus10

minus5

0

5

10

15

119905 (s)

119894 119863119894 119876

(A)

Figure 15 119894119863 (blue) and 119894119876 (green) current components

test the behavior of the fault-tolerant converter in all possiblecondition without a real disruption of the power devices

Figures 23 24 and 25 shows respectively the measure-ments of voltage on faulty and unfaulty phases and themeasurement of the currents before and after fault andreconfiguration

This final comparison validates the proposed generalmodel of VSI in healthy and faulty mode implementedalgorithm

7 Conclusions

The use of fault-tolerant systems is essential for the optimaldevelopment of electrical power production by renewablesources as well as for the achievement of high reliability

Advances in Power Electronics 9

155 156 157 158 159 16 161 162 163 164

minus5

minus4

minus3

minus2

minus1

0

1

2

3

4

5

119905 (s)

Out

put c

urre

nt (A

)

Figure 16 After fault current zoom

226 227 228 229 23 231 232 233 234minus3

minus2

minus1

0

1

2

119905 (s)

Out

put c

urre

nt (A

)

Figure 17 After fault current with no reactive power

16 165 17 175 18 185

minus200

minus100

0

100

200

Grid

vol

tage

(V)

grid

curr

ent (

A)

minus10

minus5

0

5

10

119905 (s)

Figure 18 Phase voltage (blue dashed) and current (green continu-ous) with and without Q transmission

16 165 17 175 18 185 19 195 2

minus3

minus2

minus1

0

1

2

3

4

119905 (s)

119894 119863119894 119876

(A)

Figure 19 119894119863 and 119894119876 transient after vanishing Q

15 155 16 165 17 175 18 185 19 195 205

06

07

08

09

1

11

12

13

14

15

119905 (s)

Inpu

t cur

rent

(A)

Figure 20 Transient on 1198940 after vanishing Q

Table 2 Test bench induction motor nameplates

Ratings ValuePower 55 kWSpeed 2870 rpmFrequency 50ndash60HzTorque 183NmVoltage 400VCurrent 13 APoles 2

and power quality fundamental for both end users and gridmanager

Fault tolerant converters require intelligent real-timedetection algorithms of incoming failures easy to implementeven on low cost hardware such as microcontrollers orPegasus

In this paper the authors have considered the faulttolerant operation of an inverter for distributed generation

10 Advances in Power Electronics

Figure 21 Picture of the realized test bench

Figure 22 A bidirectional switch realized with diode and IGBT

system seen as an ancillary complementary function inaddiction to the classical ones already developedThe generalinverter model here presented in the paper is suitable anduseful for the simulation of faults and fault-tolerant operationof a VSI The presented model is very helpful to predicttransient phenomena due to faults occurrence Switchingfunction definition has been extended in order to cover thecondition of diode turning on and open fault occurrenceThe introduction of HDBVs and HLBVs allows for theconstruction of a unified model suitable for simulations withequation solver tools This makes the simulations affordableand at the same time fast in their operation

The implementation algorithm is very suitable in largecontext as grid connected converter for DG because it istransparent to the action of the main power control andsynchronization

Numerical simulations presented in the paper have con-sidered both a standalone and a grid converter In order toguarantee minimal power quality degradation the followingconsiderations apply in the converter control

(i) over modulation must be avoided(ii) for this reason both a reduction of the transmitted

active power and vanishing the reactive power aremandatory

(iii) a 25ndash30 greater DC link voltage with respect totraditional value must be chosen

The control has been also verified with experimental resultsin the case of reconfigurable operation Comparison of

004 006 008 01 012 014 016 018 02Time (s)

minus250

minus200

minus150

minus100

minus50

0

50

100

150

200

250

119881119886

(V)

Figure 23 Measurement of faulty phase voltage before and after thefault

005 01 015Time (s)

minus300

minus200

minus100

0

100

200119881119887

(V)

Figure 24 Measurement of unfaulty phase voltage before and afterthe fault

002 004 006 008 01 012 014 016 018 02Time (s)

minus10

minus5

0

5

10

119894 ABC

(A)

Figure 25Measurement of phase currents before and after the fault

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Advances in Power Electronics 9

155 156 157 158 159 16 161 162 163 164

minus5

minus4

minus3

minus2

minus1

0

1

2

3

4

5

119905 (s)

Out

put c

urre

nt (A

)

Figure 16 After fault current zoom

226 227 228 229 23 231 232 233 234minus3

minus2

minus1

0

1

2

119905 (s)

Out

put c

urre

nt (A

)

Figure 17 After fault current with no reactive power

16 165 17 175 18 185

minus200

minus100

0

100

200

Grid

vol

tage

(V)

grid

curr

ent (

A)

minus10

minus5

0

5

10

119905 (s)

Figure 18 Phase voltage (blue dashed) and current (green continu-ous) with and without Q transmission

16 165 17 175 18 185 19 195 2

minus3

minus2

minus1

0

1

2

3

4

119905 (s)

119894 119863119894 119876

(A)

Figure 19 119894119863 and 119894119876 transient after vanishing Q

15 155 16 165 17 175 18 185 19 195 205

06

07

08

09

1

11

12

13

14

15

119905 (s)

Inpu

t cur

rent

(A)

Figure 20 Transient on 1198940 after vanishing Q

Table 2 Test bench induction motor nameplates

Ratings ValuePower 55 kWSpeed 2870 rpmFrequency 50ndash60HzTorque 183NmVoltage 400VCurrent 13 APoles 2

and power quality fundamental for both end users and gridmanager

Fault tolerant converters require intelligent real-timedetection algorithms of incoming failures easy to implementeven on low cost hardware such as microcontrollers orPegasus

In this paper the authors have considered the faulttolerant operation of an inverter for distributed generation

10 Advances in Power Electronics

Figure 21 Picture of the realized test bench

Figure 22 A bidirectional switch realized with diode and IGBT

system seen as an ancillary complementary function inaddiction to the classical ones already developedThe generalinverter model here presented in the paper is suitable anduseful for the simulation of faults and fault-tolerant operationof a VSI The presented model is very helpful to predicttransient phenomena due to faults occurrence Switchingfunction definition has been extended in order to cover thecondition of diode turning on and open fault occurrenceThe introduction of HDBVs and HLBVs allows for theconstruction of a unified model suitable for simulations withequation solver tools This makes the simulations affordableand at the same time fast in their operation

The implementation algorithm is very suitable in largecontext as grid connected converter for DG because it istransparent to the action of the main power control andsynchronization

Numerical simulations presented in the paper have con-sidered both a standalone and a grid converter In order toguarantee minimal power quality degradation the followingconsiderations apply in the converter control

(i) over modulation must be avoided(ii) for this reason both a reduction of the transmitted

active power and vanishing the reactive power aremandatory

(iii) a 25ndash30 greater DC link voltage with respect totraditional value must be chosen

The control has been also verified with experimental resultsin the case of reconfigurable operation Comparison of

004 006 008 01 012 014 016 018 02Time (s)

minus250

minus200

minus150

minus100

minus50

0

50

100

150

200

250

119881119886

(V)

Figure 23 Measurement of faulty phase voltage before and after thefault

005 01 015Time (s)

minus300

minus200

minus100

0

100

200119881119887

(V)

Figure 24 Measurement of unfaulty phase voltage before and afterthe fault

002 004 006 008 01 012 014 016 018 02Time (s)

minus10

minus5

0

5

10

119894 ABC

(A)

Figure 25Measurement of phase currents before and after the fault

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

10 Advances in Power Electronics

Figure 21 Picture of the realized test bench

Figure 22 A bidirectional switch realized with diode and IGBT

system seen as an ancillary complementary function inaddiction to the classical ones already developedThe generalinverter model here presented in the paper is suitable anduseful for the simulation of faults and fault-tolerant operationof a VSI The presented model is very helpful to predicttransient phenomena due to faults occurrence Switchingfunction definition has been extended in order to cover thecondition of diode turning on and open fault occurrenceThe introduction of HDBVs and HLBVs allows for theconstruction of a unified model suitable for simulations withequation solver tools This makes the simulations affordableand at the same time fast in their operation

The implementation algorithm is very suitable in largecontext as grid connected converter for DG because it istransparent to the action of the main power control andsynchronization

Numerical simulations presented in the paper have con-sidered both a standalone and a grid converter In order toguarantee minimal power quality degradation the followingconsiderations apply in the converter control

(i) over modulation must be avoided(ii) for this reason both a reduction of the transmitted

active power and vanishing the reactive power aremandatory

(iii) a 25ndash30 greater DC link voltage with respect totraditional value must be chosen

The control has been also verified with experimental resultsin the case of reconfigurable operation Comparison of

004 006 008 01 012 014 016 018 02Time (s)

minus250

minus200

minus150

minus100

minus50

0

50

100

150

200

250

119881119886

(V)

Figure 23 Measurement of faulty phase voltage before and after thefault

005 01 015Time (s)

minus300

minus200

minus100

0

100

200119881119887

(V)

Figure 24 Measurement of unfaulty phase voltage before and afterthe fault

002 004 006 008 01 012 014 016 018 02Time (s)

minus10

minus5

0

5

10

119894 ABC

(A)

Figure 25Measurement of phase currents before and after the fault

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Advances in Power Electronics 11

simulations and experimental results with the clear goodaccordance between them confirms the validity of the pro-posed model and encourages the proposed implementationalgorithm to include fault tolerance as an additional ancillaryfunction in the next generation of grid converters

Abbreviations

119895 = 119860 119861 119862 Phase indexV119895119874(119873) 119894119895 Phase voltages and currents on the AC

side119890119895119873 Back emf of the load (or grid voltages)ℎ119895plusmn Upper(+)lower(minus) healthy device binary

variablesℎ119895 Healthy leg binary variables119878119895plusmn Upper(+)lower(minus) side transistor

switching function for phase j119878119895plusmn Upper(+)lower(minus) side transistor

generalized switching function for phasej

119863119895plusmn Upper(+)lower(minus) side diode switchingfunction for phase j

otimes Logical AND operatoroplus Logical OR operator119880DC Whole inverter capacitor bank voltage1198801 1198802 Partial capacitor bank voltage1198940 DC side inverter input current1198770 1198710 DC side wires parasitic circuital

parameters119862 Value of the single DC link capacitor119877 119871 Load circuital parameter (or grid filter

resistance and inductance)[sdot sdot sdot ]119905 Transposition of a matrix (a vector)

1 = [111]119905 Unitary three-dimensional vectoruref Vector of the reference voltage in PWM

controlulowastref Vector of the reference voltage in PWM

control after a faultkk Vector of the converter output voltagesh Vector of the healthy leg binary variablesh NOT(h) vectorik Vector of the load currents

Sk Vector of the switching functions[119878119860 119878119861 119878119862]

119905

120593 Angle displacement119880119909 Phasor voltage peak120572 = exp(119895(21205873)) Fortescue operator for symmetrical

Componentsk1 times k2 Cross product between generic vectors

k1 and k2

References

[1] F Abrahamsen F Blaabjerg and C Klumpner ldquoLow inductivefuses in DC Link inverter applicationrdquo in Proceedings of thePower Conversion Intelligent Motion Conference (PCIM rsquo00)Boston Mass USA March 2000

[2] H Chen X Zhang S Liu and S Yang ldquoResearch on controlstrategies for distributed inverters in low voltage micro-gridsrdquoin Proceedings of the 2nd International Symposium on PowerElectronics for Distributed Generation Systems (PEDG rsquo10) pp748ndash752 Hefei China June 2010

[3] F Blaabjerg S Freysson H Hansen and S Hansen ldquoA newoptimized space-vector modulation strategy for a component-minimized voltage source inverterrdquo IEEE Transactions on PowerElectronics vol 12 no 4 pp 704ndash714 1997

[4] B Wang J Wang X Sun J Wu and W Wu ldquoPhase multilevelinverter fault diagnosis and tolerant control techniquerdquo inProceedings of the CESIEEE 5th International Power Electronicsand Motion Control Conference (IPEMC rsquo06) pp 1ndash5 ShanghaiChina August 2006

[5] S Duong J Schanen C Schaeffer F Sarrus and J de PalmaldquoIGBT protection by fuse calculation behaviour and connec-tionrdquo in Proceedings of the Conference Record of the IEEEIndustry Applications Conference 32nd IASAnnualMeeting (IASrsquo97) pp 1228ndash1235 New Orleans La USA 1997

[6] F Genduso R Miceli and S Favuzza ldquoA Perspective on thefuture of distribution smart grids state of the art benefits andresearch plansrdquo Energy and Power Engineering vol 5 no 1 pp36ndash42 2013

[7] J Salmon ldquoCurrent overload protection features of hybridinverter drivesrdquo in Proceedings of the International Conferenceon Power Electronics and Motion Control vol 1 pp 470ndash476San Diego CA USA November 1992

[8] M Ma L Hu A Chen and X He ldquoReconfiguration ofcarrier-based modulation strategy for fault tolerant multilevelinvertersrdquo IEEE Transactions on Power Electronics vol 22 no5 pp 2050ndash2060 2010

[9] L Zhou and K Smedley ldquoA fault tolerant control systemfor hexagram inverter motor driverdquo in Proceedings of the25th Annual IEEE Applied Power Electronics Conference andExposition (APEC rsquo10) pp 264ndash270 Palm Springs CA USAFebruary 2010

[10] D Sun and Y He ldquoA modified direct torque control for PMSMunder inverter faultrdquo in Proceedings of the 8th InternationalConference on ElectricalMachines and Systems (ICEMS rsquo05) vol3 pp 2473ndash2473 Nanjing China 2005

[11] M A Parker C Ng and L Ran ldquoFault-tolerant control fora modular generatorconverter scheme for direct-drive windturbinesrdquo IEEE Transactions on Industrial Electronics vol 58no 1 pp 305ndash315 2011

[12] O Wallmark L Harnefors and O Carlson ldquoPost-fault opera-tion of fault-tolerant inverters for PMSM drivesrdquo in Proceedingsof the European Conference on Power Electronics and Applica-tions pp 1ndash10 Dresden Germany September 2005

[13] P Correa M Pacas and J Rodriguez ldquoModulation strategiesfor fault-tolerant operation of H-bridge multilevel invertersrdquoin Proceedings of the IEEE International Symposium on Indus-trial Electronics (ISIE rsquo06) pp 1589ndash1594 Montreal QuebecCanada July 2006

[14] F Genduso R Miceli and G R Galluzzo ldquoFlexible powerconverters for the fault tolerant operation of micro-gridsrdquo inProceedings of the 19th International Conference on ElectricalMachines (ICEM rsquo10) Rome Italy September 2010

[15] B Xu D Yang and X Wang ldquoNeural network based faultdiagnosis and reconfiguration method for multilevel inverterrdquoin Proceedings of the Chinese Control and Decision Conference(CCDC rsquo08) pp 564ndash568 Yantai Shandong China July 2008

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

12 Advances in Power Electronics

[16] S BolognaniM Zordan andM Zigliotto ldquoExperimental fault-tolerant control of a PMSM driverdquo IEEE Transactions onIndustrial Electronics vol 47 no 5 pp 1134ndash1141 2000

[17] C Cecati and N Rotondale ldquoA double-PWM strategy forimproved electric drive reliabilityrdquo in Proceedings of the Sym-posium on Power Electronics Electrical Drives Automation ampMotion (SPEEDAM rsquo02) vol 1 pp 25ndash30 Ravello Italy 2002

[18] A O di Tommaso S Favuzza F Genduso R Miceli andG R Galluzzo ldquoDevelopment of diagnostic systems for thefault tolerant operation of Micro-Gridsrdquo in Proceedings of theInternational Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM rsquo10) pp 1645ndash1650 PisaItaly June 2010

[19] L Li-Chun P Ching-Tsai and T Lang-Jong ldquoSwitching flowgraph modeling technique for three phase inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 4 pp 1603ndash1613 2008

[20] S Cuk and R Middlebrook ldquoA general unified approach tomodeling switching converters power stagesrdquo in Proceedings ofthe IEEEPower Electronics Specialist Conference pp 18ndash34 1976

[21] F Genduso R Miceli and G R Galluzzo ldquoExperimentalvalidation of a generalmodel for three phase inverters operatingin healthy and faulty modesrdquo in Proceedings of the InternationalSymposium on Power Electronics Electrical Drives Automationand Motion (SPEEDAM rsquo12) pp 1ndash6 May 2012

[22] P Chen Z Ying and D Enzeng ldquoFault detection algorithmof inverter based on singular value decomposition nonlinearfilteringrdquo in Proceedings of the IEEE International Conference onComputer Science and Automation Engineering (CSAE rsquo11) vol2 pp 85ndash89 2011

[23] D Braun D Pixler and P LeMay ldquoIGBT module rupturecategorization and testingrdquo in Proceedings of the IEEE IndustryApplications Conference 32nd IAS Annual Meeting pp 1259ndash1266 October 1997

[24] C Cecati F Genduso R Miceli and G R Galluzzo ldquoA suitablecontrol technique for fault-tolerant converters in distributedgenerationrdquo in Proceedings of the International Symposium onIndustrial Electronics (ISIErsquo 11) pp 107ndash112 Gdansk PolandJune 2011

[25] F Genduso and R Miceli ldquoA general mathematical modelfor nonredundant fault-tolerant invertersrdquo in Proceedings ofthe IEEE International Electric Machines amp Drives Conference(IEMDC rsquo11) pp 705ndash710 2011

[26] F Genduso and R Miceli ldquoPower quality savings with con-trolled fault-tolerant power convertersrdquo in Proceedings of theInternational Conference onTheory and Application of Modelingand Simulation in Electrical Power Engineering (ELECTRIMACSrsquo11) pp 1ndash6 Cergy Pontoise France June 2011

[27] A D Tommaso F Genduso R Miceli and G R GalluzzoldquoA general mathematical model for the simulation of commonfaults in three phase voltage source invertersrdquo InternationalJournal of Automation and Power Engineering vol 2 pp 1ndash112013

[28] F Blaabjerg R Teodorescu M Liserre and A V TimbusldquoOverview of control and grid synchronization for distributedpower generation systemsrdquo IEEE Transactions on IndustrialElectronics vol 53 no 5 pp 1398ndash1409 2006

[29] M Liserre P Rodriguez and R TeodorescuGrid Converter forPhotovoltaic and Wind Power Systems Wiley IEEE press 2011

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of