research article reliability assessment of transformerless pv...
TRANSCRIPT
Research ArticleReliability Assessment of Transformerless PV Invertersconsidering Mission Profiles
Yongheng Yang Huai Wang and Frede Blaabjerg
Department of Energy Technology Aalborg University Pontoppidanstraede 101 9220 Aalborg Denmark
Correspondence should be addressed to Yongheng Yang yoyetaaudk
Received 27 October 2014 Revised 26 January 2015 Accepted 9 February 2015
Academic Editor Mahmoud M El-Nahass
Copyright copy 2015 Yongheng Yang et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
Due to the small volume and high efficiency transformerless inverters have gained much popularity in grid-connected PVapplications where minimizing leakage current injection is mandatory This can be achieved by either modifying the modulationschemes or adding extra power switching devices resulting in an uneven distribution of the power losses on the switching devicesConsequently the device thermal loading is redistributed and thus may alter the entire inverter reliability performance especiallyunder a long-term operation In this consideration this paper assesses the device reliability of three transformerless inverters undera yearly mission profile (ie solar irradiance and ambient temperature)Themission profile is translated to device thermal loadingwhich is used for lifetime prediction Comparison results reveal the lifetime mismatches among the power switching devicesoperating under the same condition which offers new thoughts for a robust design and a reliable operation of grid-connectedtransformerless PV inverters with high efficiency
1 Introduction
Power electronics converter technology has enabled moreand more renewable energy installations in recent yearswhich is also associatedwith an increasing demand for higherefficiency and higher reliability [1ndash7] In order to reduce thecost of energy the demand will be further strengthened inthe future energy mix dominated by wind turbine systemsand photovoltaic (PV) systems [8ndash11] Transformerless PVinverters have gained much reputation in the Europeanmarket in terms of high efficiency small size and low weightcompared to their counterparts [7 12ndash16] Its popularityand its magnificence in conversion efficiency induce a shiftin inverter technology in the United States recently [17]Therefore an evenwide-scale adoption of transformerless PVinverters in the future grid-friendly systems is predictable
Till now a vast of transformerless PV inverters have beendeveloped [13ndash20] and many of those topologies have beensuccessfully commercialized in residential PV applicationswhere size and efficiency are the main concerns Howeverldquotransformerlessrdquo are also required to minimize the leakagecurrent injections for safety due to the removal of the galvanicisolation This is typically achieved by either developing
a special suitable modulation scheme or adding extra powerswitching devices [18] For instance in [19 20] optimizationapproaches have been proposed to improve the performanceof transformerless PV inverters while in [12ndash14] additionalpower switching devices have been introduced to the tra-ditional full-bridge PV inverter However such software orhardwaremodifications will alter the power loss distributionson the power switching devices thus contributing to uneventhermal loading in the PV inverters
Due to the intermittency of solar energy transformerlessPV inverters have to handle a fluctuating power Thus thethermal loading on each power switching device will bedifferent under a long-term mission profile (eg a yearlysolar irradiance and ambient temperature profile) [21ndash24]The varying thermal loading (appears as fluctuating junctiontemperature) of the power switching devices is one of themain failure contributors for the power electronics devices[22ndash29] As a consequence the thermal stress differenceamong the power switching devices will possibly make theentire transformerless PV inverter fail to operate [25ndash32]Although more advanced transformerless inverters with amain focus on efficiency are coming on market there isstill a lack of a reliability-oriented investigation considering
Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2015 Article ID 968269 10 pageshttpdxdoiorg1011552015968269
2 International Journal of PhotoenergySo
lar i
rrad
ianc
eA
mbi
ent t
empe
ratu
re
PV stringsmodules Full-bridge
∘C
iPV
CPV
O
iCMVCMVCP
Cf
LCL-filter
Grid
Ground
S1
S2
S3
S4
D1
D2
D3
D4
L1 L2
A
B
Figure 1 A single-phase single-stage grid-connected full-bridge PVinverter systemwith an LCL-filter where VCMV is the commonmodevoltage and 119862
119875is the stray capacitor
mission profiles for those PV inverters However such aninvestigation allows new thoughts for a robust design anda reliable operation of PV system As a result a reductionof the cost can be attained since both the efficiency and thereliability of transformerless PV inverters are enhanced
Taking the above into consideration this paper exploresthe thermal performance of three selected transformerless PVinverters under a yearly mission profile which thus allows aqualitative reliability assessment of the PV inverters beyondefficiency achievements Firstly a description of the selectedtransformerless PV topologies is presented in Section 2Focus has been put on the mission profile translation to thecorresponding device thermal loading of the transformerlessinverters in Section 3 where a mission profile based relia-bility evaluation approach is also introduced In accordancewith the translated thermal loading profiles Section 4 thusconducts an assessment of the device reliability in those PVinverters before the conclusions
2 Selected Transformerless PV Inverters
Depending on the power ratings transferring PV energy toan AC power grid has several possibilities [1 7 33] It can bemodular PV converters which typically harvest the energyusing DC-DC converters (maximum power point tracking)[34ndash36] while the string or central inverters can be directlyconnected to the grid Since the grid-connected PV systemsare still dominantly designed for residential applications[33] the single-phase transformerless PV inverter system isanalyzed
Figure 1 shows the most commonly used single-phasefull-bridge (FB) PV inverter topology where the modulationschemes have to be modified for a smaller leakage current(119894CMV) As it is shown in Figure 1 an LCL-filter is used fora better power quality In some cases a DC-DC converter isadopted to boost up the PV output voltage to an acceptablelevel for the PV inverters Conventionalmodulationmethodsfor the single-stage FB inverter topology include the bipolarmodulation the unipolar modulation and the hybrid mod-ulation When considering the leakage current injection intransformerless applications the bipolar modulation schemeis preferable [12 21] which is chosen in this paper Notablyoptimizing the modulation patterns is an alternative toeliminate the leakage currents [19]
Asmentioned early transformerless structures aremostlyderived from the FB topology by providing an AC path ora DC path using additional power switching devices As aresult during the zero-voltage states isolation between thePV modules and the grid is achieved thus leading to a lowleakage current injection Figure 2 shows two examples oftransformerless PV inverters derived from the single-phaseFB topology As it can be seen in Figure 2(a) the H6 invertertopology [13] has a DC path which isolates the PV panelsfrom the grid at zero-voltage states In contrast although thehighly efficient and reliable inverter concept (HERIC) [14]inverter has the same number of power switching devices asthat of the H6 inverter it provides an AC path to eliminatethe leakage current injection
It should be pointed out that there are also many othertransformerless topologies reported in the literature in addi-tion to the above two solutions [12 16 37] For examplethe Conergy neutral point clamped (NPC) transformerlessPV inverter is based on the multilevel power convertertechnology [12 20] However only the FB inverter with abipolar modulation scheme (FB-Bipolar) the H6 inverterand the HERIC inverter are assessed in terms of reliability
3 Mission Profile Translation toThermal Loading
31 Mission Profile for PV Systems A mission profile isnormally referred to a simplified representation of relevantconditions under which the system is operating [27 32] As aresult for the grid-connected PV systems the mission profile(ie solar irradiance and ambient temperature) is actually areflection of the intermittent nature of the solar PV energy[38 39] and consequently it has an inherent relationshipwith the entire system performance including the thermalloading performance The mission profile can be a series ofmultitime scales for example a minute mission profile ora yearly mission profile and it is usually taken as the inputfor the reliability analysis in the field of power electronicsconverters [29 39ndash42] which is also focused on in this paperFigure 3 shows the mission profile applied to the above threetransformerless PV inverters
With more accumulative real-field experience and moreadvanced real-time monitoring technology better missionprofiles are available for a reasonable lifetime predictionHence a mission profile based analysis approach should beable to analyze the performance at different time scales asit is shown in Figure 4 It can be observed in Figure 4(a)that for short-term mission profiles at the level of millisec-onds to several seconds the thermal loading profile canbe directly and instantaneously obtained In contrast forlong-term mission profiles within a range of a few minutesto several months obtaining the instantaneous thermalloading will be very time-consuming or even impossiblewhen the mission profile has a high data-sampling rateAlternatively the thermal loading profile can be obtainedbased on lookup tables [43] which are created in accordancewith the short-term constantmission profiles as it is shown inFigure 4(b)
International Journal of Photoenergy 3
PV stringsmodules Full-bridgeiPV
CPV1
CPV2
CP
LCL-filter
DC path
Grid∘C
OSola
r irr
adia
nce
Am
bien
t tem
pera
ture
Cf
S1
S2
S3
S4
S5
S6
D3
D2
D1
D6
D5
D4
D8
D7L1 L2
A
B
(a)
PV stringsmodules Full-bridge
iPV
CPV
CP
LCL-filter
AC path
Grid∘C
OSola
r irr
adia
nce
Am
bien
t tem
pera
ture
Cf
S1
S2
S3
S4
S5
S6
D3
D2
D1
D6
D5
D4
L1 L2A
B
(b)
Figure 2 Examples of single-phase transformerless PV inverters derived from the single-phase full-bridge topology by adding extra powerswitching devices (a) H6 inverter [13] and (b) HERIC inverter [14]
Sola
r irr
adia
nce (
kWm
2)
15
10
05
0Oct Nov Dec Jan Feb Mar Apr Jun Jul Aug SepMay
(a)
Am
bien
t tem
p (∘
C)
40
20
0
minus20Oct Nov Dec Jan Feb Mar Apr Jun Jul Aug SepMay
(b)
Figure 3 A yearly mission profile used for the selected transformerless PV inverters (1 secsample) (a) solar irradiance and (b) ambienttemperature
∘C
MPPTMiss
ion
profi
le GridElectricalsystem
PVmodels
PinPout
PlossTransformerlessPV inverters
(electrical andloss models)
TjTj
Thermalmodel
Thermalloading profile
(a)
∘C
Lookup tablebased
simulation (thermal) model
Miss
ion
profi
le
Tj Thermalloading profile
(b)
Figure 4 Approach of the mission profile translation to thermal loading at different time scales (MPPT maximum power point tracking 119879119895
junction temperature of the power devices) (a) short-term mission profiles and (b) long-term mission profiles
32 Thermal Modelling of Power Switching Devices As it isshown in Figure 4 the translation from a mission profileto the corresponding thermal loading profile requires athermalmodel which links the electrical performance (powerlosses 119875loss) and the thermal behavior (junction temperature119879119895) The coupled relationship is demonstrated in Figure 5
in a FB PV inverter system which shows that the powerlosses on the switching devices will introduce a temperaturerise due to the thermal impedance in the power switchingdevices The thermal impedance can be modeled as a Fostermodel [43ndash47] as it is shown in Figure 6 Details of thethermal modelling of power semiconductors can be found in[46 47]
Typically for such a model of the thermal impedance theparameter data is provided in the datasheet Table 1 showsthe thermal parameters of the power switching device froma leading manufacturer used in the paper Notably all thedevices are the same in the three transformerless PV invertersfor comparison in terms of thermal loading and thus thebenchmarking results indicating the critical components of
Table 1Thermal impedance parameters of power switching devicesfrom a leading manufacturer according to Figure 6
Impedance 119885th(119895-119888)
119894 1 2 3 4IGBT119877th119894 (KW) 0074 0173 0526 0527120591119894(s) 00005 0005 005 02
Diode119877th119894 (KW) 0123 0264 0594 0468120591119894(s) 00005 0005 005 02
transformerless PV inverters could be a guidance to selectappropriate power switching devices in such applications
33 Translated Thermal Loading to Lifetime Based on thethermal model simulations have been carried out in PLECS[43] according to Figure 4 where the system parameters are
4 International Journal of Photoenergy
Power losses Device temp
Electrical domain
Thermal domain
Junction Case Heat-sink Ambient
Pin Poutinvdc
(Ploss = Pin minus Pout)Tj Tc Th Ta
Zth(j-c)Zth(c-h) Zth(h-a)
Figure 5 Coupled relationship between power losses and the junction temperature of the power switching devices 119885th(119895-119888) junction to caseimpedance 119885th(119888-ℎ) case to heat-sink impedance and 119885th(ℎ-119886) heat-sink to ambient impedance
Tc
Tj
Ptot
Ta
Rth1 Rth2 Rth3 Rth4
C1 C2 C3 C4
Ci = 120591iRthiZth(j-c)
Figure 6 Foster model of the junction to case thermal impedance 119885th(119895-119888) shown in Figure 5
Table 2 System parameters for single-phase transformerless grid-connected PV systems
Parameter Symbol Value UnitGrid voltage V
119892RMS 230 VGrid frequency 119891
119892 50 Hz
LCL-filter1198711
36 mH119862119891 235 120583F
1198712
4 mHDamping resistor 119877
11988910 Ω
Switching frequency 119891119904
10 kHzParameters of PV strings (3 strings 15 panels for each string)
at 25∘C and 1 kWm2
Power at MPP 119875MPP 299 kWVoltage at MPP 119881MPP 405 VCurrent at MPP 119868MPP 738 A
shown in Table 2 In order to create the lookup tables forlong-termmission profiles several constant operating condi-tions (eg solar irradiance 08 kWm2 ambient temperature25∘C) have been simulated firstly where a perturb-and-observe maximum power point (MPP) tracking algorithmhas been used [33ndash35 38] Figure 7 exemplifies the simulationmodel for a full-bridge inverter system A proportional reso-nant current controller has been adopted to control the gridcurrent considering power quality requirements [2] Using
the lookup table model the yearly mission profile (Figure 3)has been resampled (5minssample) and translated intothe thermal loading of the corresponding power switchingdevices as it is presented in Figure 8
Although the transformerless PV inverters (both the H6and the HERIC) can maintain a higher efficiency as reportedin the literature in contrast to the FB-Bipolar inverter thethermal loading on those switching devices is unequal as itcan be seen in Figure 8 Specifically the maximum junctiontemperature of the extra devices in an H6 inverter is thehighest indicating high power losses since they are switchedat a high frequency However this is not the case for theHERIC inverter where only one of the extra switchingdevices is switched at the grid frequency during a half cycleTherefore the power losses are lower and thus the thermalloading as it is shown in Figure 8 From the above qualitativeanalysis it is implied that much attention has to be paid onthe extra switching devices in transformerless PV invertersParticularly for theH6 inverter power switching deviceswithlower conduction losses and higher rated maximum junctiontemperature are desirable while the total cost has to be takeninto consideration as well
When the thermal loading profile appearing in the powerswitching devices is available a quantitative prediction ofthe device lifetime under the mission profile is enabled by arain-flow counting algorithm [41 42]The rain-flow countingalgorithm is a quantitative representation of the thermalloading which extracts the temperature information in detailin terms of the mean junction temperature 119879
119895119898 temperature
International Journal of Photoenergy 5
STa
PV++
+++
+
minus
minus
A
CC
A
V VCPVC 11e minus 3
PV
iPV
PWM
1
2 345
Full-bridgeinverter
a
a
b
b
R1 R2L1 L2
Cf GridRd
s
ig
gControl system
Probe
Probe
Probe
Probe
Probe
Probe
Probe
Probe
ProbeVac
Iac
PV V I P
PV P V
AC grid
PV string
P versus V
s
+
minus
f(u)
f(u)
f(u)
f(u)
D1
D2 D4
D3
Heat sink
IGBT1
IGBT2
IGBT3
IGBT4
Scope
Thermal chain T tint
Figure 7 Simulation model of a single-phase full-bridge PV inverter system in PLECS
FB-bipolar
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
S1ndash4
S1ndash4
S1ndash4
1011 0312 0912Time of a year (monthyear)
1011 0312 0912Time of a year (monthyear)
1011 0312 0912Time of a year (monthyear)
H6
Extra devices S56
Extra devices S56
HERIC
(a)
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
S1ndash4
S1ndash4
S1ndash4
Extra devices S56
Extra devices S56
Time of a day (hoursmin)0000 1200 2400
Time of a day (hoursmin)0000 1200 2400
Time of a day (hoursmin)0000 1200 2400
(b)
Figure 8 Translated thermal loading (maximum junction temperature 119879119895max) of the power switching devices of the three different
transformerless grid-connected PV inverters under a yearly mission profile shown in Figure 3 (a) the yearly long-term thermal loadingand (b) details of the maximum junction temperature of the power switching devices in a cloudy day of the year
6 International Journal of Photoenergy
Table 3 Parameters of the lifetime model for power devices [48]
Parameter Value Unit Experimental condition119860 34368 times 1014 mdash120572 minus4923 mdash 64K le Δ119879
119895le 113 K
1205730
1942 mdash 019 le ar le 0421205731
minus9012 times 10minus3 mdash119862 1434 mdash 007 s le 119905
119900119899le 63 s
120574 minus1208 mdash119891119889
06204 mdash119864119886
006606 eV 325∘C le 119879119895119898
le 122∘C119896119861
86173324 times 10minus5 eVK
cycle amplitude 119879119895 cycle period 119905
119900119899 number of cycles n and
so forthThen the extracted temperature information can beused for the lifetime prediction according to a specific lifetimemodel For example a lifetime model of power switchingdevices is introduced in [48] and it can be expressed as
119873119891= 119860Δ119879
120572
119895(119886119903)1205731Δ119879119895+1205730 (
119862 + (119905119900119899)120574
119862 + 1) exp(
119864119886
119896119861119879119895119898
)119891119889
(1)
where119873119891is the number of cycles to fail119891
119889is the diode effect
119886119903 is the bond-wire aspect ratio 119896119861is the Boltzmann constant
119864119886is the activation energy and 119860 120572 120573
0 1205731 120574 and 119862 are
the lifetime model parameters as it is shown in Table 3 Thelifetime model also implies that the junction temperature hasa significant impact on the number of cycles to fail that is thereliability of the power switching devices
According to Minerrsquos rule [24 42 48] the life consump-tion LC the damage due to the thermal stress is the linearlyaccumulative damage from different thermal cycles The LCcan then be expressed as
119871119862 = sum
119894
119899119894
119873119891119894
(2)
in which 119899119894is the number of cycles at the stressΔ119879
119895119894extracted
by the rain-flow counting algorithm and 119873119891119894is the number
of cycles to fail based on (1) Subsequently the lifetime of thepower switching devices can be given as
119871119875=119905119872119875
119871119862(3)
with 119871119875being the predicted lifetime and 119905
119872119875being the
mission profile period (eg a year)Using the above reliability analysis procedure the lifetime
of the power switching devices in the transformerless PVinverters can then be estimated as long as a mission profileand a lifetimemodel of high confidence are available Figure 9summarizes the mission profile based analysis approachwhich can also be used in other power electronics convertersfor example wind turbine converters where the missionprofiles are available
Mission profile
Mission profiletranslation
Thermal loadinginterpretation
Lifetimeprediction
∘C
System models
Loading profilecounting
Lifetimemodels
Counting algorithms
Extracted thermal info
∙ Level crossing∙ Rain-flow∙ Simple range counting∙ middot middot middot
∙ middot middot middot
∙ Tjm-mean junction temp∙ ΔTj-temp cycle amplitude∙ ton -cycle period
Figure 9 Flowchart of the mission profile based reliability analysisapproach for transformerless PV inverters
4 Reliability Assessment
According to Figure 9 the lifetime of the power switchingdevices in the three transformerless PV inverters under theyearly mission profile shown in Figure 3 can be obtained andevaluated In order to benchmark the reliability quantita-tively the thermal loading profiles have to be interpreted firstaccording to (1) and Figure 9 A rain-flow counting algorithmhas been adopted and the results are presented in Figure 10It can be observed in Figure 10 that the additional devicesof the H6 inverter (ie S
5and S
6) have a larger number
of cycles compared to the other power switching devices ofthis topology (S
1sim4) This indicates that the extra devices to
realize an elimination of the leakage currents become themost critical components of the H6 inverter according to(2) and (3) As a consequence more reliable power devicesare preferable as the extra devices when designing an H6based transformerless PV system In the case of the HERICinverter based transformerless PV systems the extra deviceshave a smaller number of cycles compared to those of theH6 inverter Moreover the number of cycles of the otherpower switching devices of theHERC inverter is even smallerthan that of the FB-Bipolar inverter under the same missionprofile This means that the thermal stress on the powerswitching devices of the HERIC inverter is the lowest andthus the HERIC inverter can achieve the highest reliabilityif the same mission profile is applied to those invertercandidates while also maintaining a higher efficiency as itis reported in [12 14] The discussion is in agreement withthe analysis presented in Section 33 based on the translatedthermal loading profiles
It should be noted that the life consumption and thusthe lifetime of the power switching devices according to (2)and (3) can quantitatively be obtained on condition that thelifetime model of (1) and also the parameters given in Table 3are at a high confident level However those parameters are
International Journal of Photoenergy 7
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
(a)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15 minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
S56
S56
(b)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4S56
S56
(c)
Figure 10 Rain-flowing counting results (number of cycles distributions at the cycle amplitude Δ119879119895and the mean junction temperature 119879
119895119898)
of the thermal loading profiles shown in Figure 8 (a) FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
8 International Journal of Photoenergy
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
(a)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
S56
(b)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4S56
(c)
Figure 11 Normalized life consumption (lifetime comparison) of the three transformerless PV inverters under the same mission profile (a)FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
extracted under specific conditions (eg 007 s le 119905119900119899
le
63 s) for the power switching devices introduced in [48]Therefore quantitative prediction errors will be inevitableIn order to reduce the parameter dependency and also thereliability model dependency the life consumption given in(2) is normalized and substituting (1) yields
119871119862 =119871119862
119871119862119887
= (sum
119894
119899119894
(Δ119879119895119894)120572
(119886119903)1205731Δ119879119895119894 [119862 + (119905
119900119899119894)120574] 119890119864119886(119896119861119879119895119898119894))
sdot (sum
119897
119899119897
(Δ1198791015840
119895119897)120572
(119886119903)1205731Δ1198791015840
119895119897 [119862 + (1199051015840
119900119899119897)120574] 119890119864119886(1198961198611198791015840
119895119898119897)
)
minus1
(4)
where 119871119862 is the normalized life consumption and LCb is thebase LC for normalization For example LCb can be chosenas the life consumption of the power switching devices of theFB-Bipolar inverter under the samemission profileThen thepredicted lifetime can be expressed as
119871119901=
1
1198711198621198711015840
119901(5)
in which 1198711015840
119901is the predicted lifetime of the base system used
for normalizationFigure 11 shows the normalized life consumption of the
three transformerless PV inverters according to (4) and thecounting results enabled by a rain-flow algorithm The lifeconsumption of the power switching devices of the FB-Bipolar (ie S
1sim4) is selected as the base life consumption for
normalization in Figure 11 It can be seen in Figure 11 that theextra power switching devices of the H6 inverter consumemuch more life compared to the other devices and also thoseof the HERIC inverter It implies that the degradation of theadditional devices of the H6 inverter happens much fasterand then the entire H6 systemmay fail to operate earlier thanthe other two transformerless PV inverters This comparisonfurther confirms that the HERIC inverter would be the mostpromising solution in terms of reliability
In addition by comparing the rain-flow counting resultsshown in Figure 10 with the normalized life consumptionshown in Figure 11 one interesting conclusion can be drawnwhich is that although there are a few cycles of a largetemperature cycling amplitude (eg ten cycles of 55∘C to65∘C for the extra devices S
56of the H6 inverter) they do
contribute much more damage (eg 04 in Figure 11(b))when the lifetime model of (1) is adopted Large cyclingamplitude is mainly induced by the mission profile whichconfirms that the mission profile effect has to be taken intoaccount in a reliability-oriented design of power electronics
International Journal of Photoenergy 9
converters In a word the reliability assessment in this paperreveals that much attention has to be put on the thermaldesign of the critical components in an entire PV inverter inorder to reduce the cost of energy
5 Conclusions
In this paper a qualitative reliability assessment of threeselected single-phase transformerless PV inverters has beencarried out in accordance with a mission profile based reli-ability analysis approach A real-field yearly mission profilehas been applied to the selected transformerless candidatesfor the reliability assessment The comparison results haverevealed that although minimizing leakage currents as wellas maintaining a satisfactory efficiency has been targetedby those inverters the extra devices that are used fordisconnection of the PV panels or the PV inverters mightbe heated up during operation The high thermal loadingwill further induce failures of the power switching devicesbeing a big challenge to the entire system reliability As aconsequence many efforts should be devoted to a reliability-oriented design of the critical components in a PV inverterand thus a reduced cost of energy can be achieved
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F Blaabjerg K Ma and Y Yang ldquoPower electronicsmdashthe keytechnology for renewable energy systemsrdquo in Proceedings ofthe 9th International Conference on Ecological Vehicles andRenewable Energies (EVER rsquo14) pp 1ndash11 Monte-Carlo MonacoMarch 2014
[2] 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
[3] J M Carrasco L G Franquelo J T Bialasiewicz et al ldquoPower-electronic systems for the grid integration of renewable energysources a surveyrdquo IEEE Transactions on Industrial Electronicsvol 53 no 4 pp 1002ndash1016 2006
[4] J D vanWyk and F C Lee ldquoOn a future for power electronicsrdquoIEEE Journal of Emerging and Selected Topics in Power Electron-ics vol 1 no 2 pp 59ndash72 2013
[5] A Golnas ldquoPV system reliability an operatorrsquos perspectiverdquoIEEE Journal of Photovoltaics vol 3 no 1 pp 416ndash421 2013
[6] A Ristow M Begovic A Pregelj and A Rohatgi ldquoDevelop-ment of a methodology for improving photovoltaic inverterreliabilityrdquo IEEE Transactions on Industrial Electronics vol 55no 7 pp 2581ndash2592 2008
[7] E Romero-Cadaval G Spagnuolo L G Franquelo C ARamos-Paja T Suntio and W M Xiao ldquoGrid-connectedphotovoltaic generation plants components and operationrdquoIEEE Industrial ElectronicsMagazine vol 7 no 3 pp 6ndash20 2013
[8] REN21 ldquoRenewables 2014 global status reportrdquo Tech Rep 2014httpwwwren21net
[9] M Liserre T Sauter and J Y Hung ldquoFuture energy systemsintegrating renewable energy sources into the smart power
grid through industrial electronicsrdquo IEEE Industrial ElectronicsMagazine vol 4 no 1 pp 18ndash37 2010
[10] C-L Shen and S-H Yang ldquoMulti-input converter with MPPTfeature for wind-PV power generation systemrdquo InternationalJournal of Photoenergy vol 2013 Article ID 129254 13 pages2013
[11] F Blaabjerg and K Ma ldquoFuture on power electronics for windturbine systemsrdquo IEEE Journal of Emerging and Selected Topicsin Power Electronics vol 1 no 3 pp 139ndash152 2013
[12] R TeodorescuM Liserre and P RodriguezGrid Converters forPhotovoltaic and Wind Power Systems Wiley-IEEE Press 2011
[13] R Gonzalez J Lopez P Sanchis and L Marroyo ldquoTrans-formerless inverter for single-phase photovoltaic systemsrdquo IEEETransactions on Power Electronics vol 22 no 2 pp 693ndash6972007
[14] H Schmidt C Siedle and J Ketterer ldquoDCAC converter toconvert direct electric voltage into alternating voltage or intoalternating currentrdquo US Patent 7046534 2006
[15] T Kerekes M Liserre R Teodorescu C Klumpner and MSumner ldquoEvaluation of three-phase transformerless photo-voltaic inverter topologiesrdquo IEEE Transactions on Power Elec-tronics vol 24 no 9 pp 2202ndash2211 2009
[16] R Gonzalez E Gubıa J Lopez and L Marroyo ldquoTransformer-less single-phase multilevel-based photovoltaic inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 7 pp 2694ndash2702 2008
[17] Advanced Energy ldquoWhatrsquos ahead for PV inverter technologyrdquoGreentechsolar 2014 httpwwwgreentechmediacom
[18] I Patrao E Figueres F Gonzalez-Espın and G GarceraldquoTransformerless topologies for grid-connected single-phasephotovoltaic invertersrdquo Renewable and Sustainable EnergyReviews vol 15 no 7 pp 3423ndash3431 2011
[19] N Achilladelis E Koutroulis and F Blaabjerg ldquoOptimizedpulse width modulation for transformerless active-NPC invert-ersrdquo in Proceedings of the 16th European Conference on PowerElectronics and Applications (EPE rsquo14-ECCE Europe) pp 1ndash10Lappeenranta Finland August 2014
[20] S Saridakis E Koutroulis and F Blaabjerg ldquoOptimal design ofmodern transformerless PV inverter topologiesdrdquo IEEE Trans-actions on Energy Conversion vol 28 no 2 pp 394ndash404 2013
[21] Y Yang H Wang F Blaabjerg and K Ma ldquoMission profilebased multi-disciplinary analysis of power modules in single-phase transformerless photovoltaic invertersrdquo in Proceedingsof the 15th European Conference on Power Electronics andApplications (EPE rsquo13) pp 1ndash10 IEEE Lille France September2013
[22] S E de Leon-Aldaco H Calleja F Chan and H R Jimenez-Grajales ldquoEffect of the mission profile on the reliability of apower converter aimed at photovoltaic applicationsmdasha casestudyrdquo IEEE Transactions on Power Electronics vol 28 no 6pp 2998ndash3007 2013
[23] H Wang M Liserre and F Blaabjerg ldquoToward reliable powerelectronics challenges design tools and opportunitiesrdquo IEEEIndustrial Electronics Magazine vol 7 no 2 pp 17ndash26 2013
[24] H Huang and P A Mawby ldquoA lifetime estimation techniquefor voltage source invertersrdquo IEEE Transactions on PowerElectronics vol 28 no 8 pp 4113ndash4119 2013
[25] P McCluskey ldquoReliability of power electronics under thermalloadingrdquo in Proceedings of the 7th International Conference onIntegrated Power Electronics Systems (CIPS rsquo12) March 2012
10 International Journal of Photoenergy
[26] H Lu C Bailey and C Yin ldquoDesign for reliability of powerelectronics modulesrdquoMicroelectronics Reliability vol 49 no 9ndash11 pp 1250ndash1255 2009
[27] M Ciappa ldquoLifetime prediction on the base ofmission profilesrdquoMicroelectronics Reliability vol 45 no 9-11 pp 1293ndash1298 2005
[28] F Chan and H Calleja ldquoReliability estimation of three single-phase topologies in grid-connected PV systemsrdquo IEEE Trans-actions on Industrial Electronics vol 58 no 7 pp 2683ndash26892011
[29] K Ma M Liserre F Blaabjerg and T Kerekes ldquoThermalloading and lifetime estimation for power device consideringmission profiles in wind power converterrdquo IEEE Transactionson Power Electronics vol 30 no 2 pp 590ndash602 2015
[30] S Harb and R S Balog ldquoReliability of candidate pho-tovoltaic module-integrated-inverter (PV-MII) topologiesmdashausagemodel approachrdquo IEEE Transactions on Power Electronicsvol 28 no 6 pp 3019ndash3027 2013
[31] P Zhang YWangW Xiao andW Li ldquoReliability evaluation ofgrid-connected photovoltaic power systemsrdquo IEEETransactionson Sustainable Energy vol 3 no 3 pp 379ndash389 2012
[32] S E De Leon-Aldaco H Calleja and J Aguayo ldquoReliability andmission profiles of photovoltaic systems a FIDES approachrdquoIEEE Transactions on Power Electronics vol 30 no 5 pp 2578ndash2586 2015
[33] S B Kjaer J K Pedersen and F Blaabjerg ldquoA review of single-phase grid-connected inverters for photovoltaicmodulesrdquo IEEETransactions on Industry Applications vol 41 no 5 pp 1292ndash1306 2005
[34] H Li J PengW Liu Z Huang andK-C Lin ldquoA newton-basedextremumseekingMPPTmethod for photovoltaic systemswithstochastic perturbationsrdquo International Journal of Photoenergyvol 2014 Article ID 938526 13 pages 2014
[35] D Sera L Mathe T Kerekes S V Spataru and R TeodoresculdquoOn the perturb-and-observe and incremental conductancemppt methods for PV systemsrdquo IEEE Journal of Photovoltaicsvol 3 no 3 pp 1070ndash1078 2013
[36] M Abdulkadir A H M Yatim and S T Yusuf ldquoAn improvedPSO-based MPPT control strategy for photovoltaic systemsrdquoInternational Journal of Photoenergy vol 2014 Article ID818232 11 pages 2014
[37] Y Zhou and H Li ldquoAnalysis and suppression of leakage cur-rent in cascaded-multilevel-inverter-based PV systemsrdquo IEEETransactions on Power Electronics vol 29 no 10 pp 5265ndash52772014
[38] A Hajiah T Khatib K Sopian and M Sebzali ldquoPerformanceof grid-connected photovoltaic system in two sites in KuwaitrdquoInternational Journal of Photoenergy vol 2012 Article ID178175 7 pages 2012
[39] M Musallam C Yin C Bailey and M Johnson ldquoMissionprofile-based reliability design and real-time life consumptionestimation in power electronicsrdquo IEEE Transactions on PowerElectronics vol 30 no 5 pp 2601ndash2613 2015
[40] Y Yang HWang F Blaabjerg and T Kerekes ldquoA hybrid powercontrol concept for PV inverters with reduced thermal loadingrdquoIEEE Transactions on Power Electronics vol 29 no 12 pp 6271ndash6275 2014
[41] A T Bryant P A Mawby P R Palmer E Santi and J LHudgins ldquoExploration of power device reliability using com-pact device models and fast electrothermal simulationrdquo IEEETransactions on Industry Applications vol 44 no 3 pp 894ndash903 2008
[42] M Musallam and C M Johnson ldquoAn efficient implementationof the rainflow counting algorithm for life consumption estima-tionrdquo IEEE Transactions on Reliability vol 61 no 4 pp 978ndash986 2012
[43] Plexim Gmbh ldquoPLECSmdashthe simulation platform for powerelectronics systemsrdquo Workshop Documentation 1 Aalborg2014
[44] I F Kovacevic U Drofenik and J W Kolar ldquoNew physicalmodel for lifetime estimation of powermodulesrdquo in Proceedingsof the International Power Electronics Conference (IPEC rsquo10) pp2106ndash2114 Sapporo Japan June 2010
[45] C Busca R Teodorescu F Blaabjerg et al ldquoAn overview ofthe reliability prediction related aspects of high power IGBTsin wind power applicationsrdquoMicroelectronics Reliability vol 51no 9ndash11 pp 1903ndash1907 2011
[46] ABB ldquoApplication NotemdashApplying IGBTsrdquo 2014 httpwwwabbcom
[47] A Volke and M Hornkamp IGBT ModulesmdashTechnologiesDriver and Application Infineon Technologies AG MunichGermany 2012
[48] U Scheuermann ldquoReliability of advanced power modules forextended maximum junction temperaturesrdquo Bodorsquos Power Sys-tems pp 26ndash30 2014
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
2 International Journal of PhotoenergySo
lar i
rrad
ianc
eA
mbi
ent t
empe
ratu
re
PV stringsmodules Full-bridge
∘C
iPV
CPV
O
iCMVCMVCP
Cf
LCL-filter
Grid
Ground
S1
S2
S3
S4
D1
D2
D3
D4
L1 L2
A
B
Figure 1 A single-phase single-stage grid-connected full-bridge PVinverter systemwith an LCL-filter where VCMV is the commonmodevoltage and 119862
119875is the stray capacitor
mission profiles for those PV inverters However such aninvestigation allows new thoughts for a robust design anda reliable operation of PV system As a result a reductionof the cost can be attained since both the efficiency and thereliability of transformerless PV inverters are enhanced
Taking the above into consideration this paper exploresthe thermal performance of three selected transformerless PVinverters under a yearly mission profile which thus allows aqualitative reliability assessment of the PV inverters beyondefficiency achievements Firstly a description of the selectedtransformerless PV topologies is presented in Section 2Focus has been put on the mission profile translation to thecorresponding device thermal loading of the transformerlessinverters in Section 3 where a mission profile based relia-bility evaluation approach is also introduced In accordancewith the translated thermal loading profiles Section 4 thusconducts an assessment of the device reliability in those PVinverters before the conclusions
2 Selected Transformerless PV Inverters
Depending on the power ratings transferring PV energy toan AC power grid has several possibilities [1 7 33] It can bemodular PV converters which typically harvest the energyusing DC-DC converters (maximum power point tracking)[34ndash36] while the string or central inverters can be directlyconnected to the grid Since the grid-connected PV systemsare still dominantly designed for residential applications[33] the single-phase transformerless PV inverter system isanalyzed
Figure 1 shows the most commonly used single-phasefull-bridge (FB) PV inverter topology where the modulationschemes have to be modified for a smaller leakage current(119894CMV) As it is shown in Figure 1 an LCL-filter is used fora better power quality In some cases a DC-DC converter isadopted to boost up the PV output voltage to an acceptablelevel for the PV inverters Conventionalmodulationmethodsfor the single-stage FB inverter topology include the bipolarmodulation the unipolar modulation and the hybrid mod-ulation When considering the leakage current injection intransformerless applications the bipolar modulation schemeis preferable [12 21] which is chosen in this paper Notablyoptimizing the modulation patterns is an alternative toeliminate the leakage currents [19]
Asmentioned early transformerless structures aremostlyderived from the FB topology by providing an AC path ora DC path using additional power switching devices As aresult during the zero-voltage states isolation between thePV modules and the grid is achieved thus leading to a lowleakage current injection Figure 2 shows two examples oftransformerless PV inverters derived from the single-phaseFB topology As it can be seen in Figure 2(a) the H6 invertertopology [13] has a DC path which isolates the PV panelsfrom the grid at zero-voltage states In contrast although thehighly efficient and reliable inverter concept (HERIC) [14]inverter has the same number of power switching devices asthat of the H6 inverter it provides an AC path to eliminatethe leakage current injection
It should be pointed out that there are also many othertransformerless topologies reported in the literature in addi-tion to the above two solutions [12 16 37] For examplethe Conergy neutral point clamped (NPC) transformerlessPV inverter is based on the multilevel power convertertechnology [12 20] However only the FB inverter with abipolar modulation scheme (FB-Bipolar) the H6 inverterand the HERIC inverter are assessed in terms of reliability
3 Mission Profile Translation toThermal Loading
31 Mission Profile for PV Systems A mission profile isnormally referred to a simplified representation of relevantconditions under which the system is operating [27 32] As aresult for the grid-connected PV systems the mission profile(ie solar irradiance and ambient temperature) is actually areflection of the intermittent nature of the solar PV energy[38 39] and consequently it has an inherent relationshipwith the entire system performance including the thermalloading performance The mission profile can be a series ofmultitime scales for example a minute mission profile ora yearly mission profile and it is usually taken as the inputfor the reliability analysis in the field of power electronicsconverters [29 39ndash42] which is also focused on in this paperFigure 3 shows the mission profile applied to the above threetransformerless PV inverters
With more accumulative real-field experience and moreadvanced real-time monitoring technology better missionprofiles are available for a reasonable lifetime predictionHence a mission profile based analysis approach should beable to analyze the performance at different time scales asit is shown in Figure 4 It can be observed in Figure 4(a)that for short-term mission profiles at the level of millisec-onds to several seconds the thermal loading profile canbe directly and instantaneously obtained In contrast forlong-term mission profiles within a range of a few minutesto several months obtaining the instantaneous thermalloading will be very time-consuming or even impossiblewhen the mission profile has a high data-sampling rateAlternatively the thermal loading profile can be obtainedbased on lookup tables [43] which are created in accordancewith the short-term constantmission profiles as it is shown inFigure 4(b)
International Journal of Photoenergy 3
PV stringsmodules Full-bridgeiPV
CPV1
CPV2
CP
LCL-filter
DC path
Grid∘C
OSola
r irr
adia
nce
Am
bien
t tem
pera
ture
Cf
S1
S2
S3
S4
S5
S6
D3
D2
D1
D6
D5
D4
D8
D7L1 L2
A
B
(a)
PV stringsmodules Full-bridge
iPV
CPV
CP
LCL-filter
AC path
Grid∘C
OSola
r irr
adia
nce
Am
bien
t tem
pera
ture
Cf
S1
S2
S3
S4
S5
S6
D3
D2
D1
D6
D5
D4
L1 L2A
B
(b)
Figure 2 Examples of single-phase transformerless PV inverters derived from the single-phase full-bridge topology by adding extra powerswitching devices (a) H6 inverter [13] and (b) HERIC inverter [14]
Sola
r irr
adia
nce (
kWm
2)
15
10
05
0Oct Nov Dec Jan Feb Mar Apr Jun Jul Aug SepMay
(a)
Am
bien
t tem
p (∘
C)
40
20
0
minus20Oct Nov Dec Jan Feb Mar Apr Jun Jul Aug SepMay
(b)
Figure 3 A yearly mission profile used for the selected transformerless PV inverters (1 secsample) (a) solar irradiance and (b) ambienttemperature
∘C
MPPTMiss
ion
profi
le GridElectricalsystem
PVmodels
PinPout
PlossTransformerlessPV inverters
(electrical andloss models)
TjTj
Thermalmodel
Thermalloading profile
(a)
∘C
Lookup tablebased
simulation (thermal) model
Miss
ion
profi
le
Tj Thermalloading profile
(b)
Figure 4 Approach of the mission profile translation to thermal loading at different time scales (MPPT maximum power point tracking 119879119895
junction temperature of the power devices) (a) short-term mission profiles and (b) long-term mission profiles
32 Thermal Modelling of Power Switching Devices As it isshown in Figure 4 the translation from a mission profileto the corresponding thermal loading profile requires athermalmodel which links the electrical performance (powerlosses 119875loss) and the thermal behavior (junction temperature119879119895) The coupled relationship is demonstrated in Figure 5
in a FB PV inverter system which shows that the powerlosses on the switching devices will introduce a temperaturerise due to the thermal impedance in the power switchingdevices The thermal impedance can be modeled as a Fostermodel [43ndash47] as it is shown in Figure 6 Details of thethermal modelling of power semiconductors can be found in[46 47]
Typically for such a model of the thermal impedance theparameter data is provided in the datasheet Table 1 showsthe thermal parameters of the power switching device froma leading manufacturer used in the paper Notably all thedevices are the same in the three transformerless PV invertersfor comparison in terms of thermal loading and thus thebenchmarking results indicating the critical components of
Table 1Thermal impedance parameters of power switching devicesfrom a leading manufacturer according to Figure 6
Impedance 119885th(119895-119888)
119894 1 2 3 4IGBT119877th119894 (KW) 0074 0173 0526 0527120591119894(s) 00005 0005 005 02
Diode119877th119894 (KW) 0123 0264 0594 0468120591119894(s) 00005 0005 005 02
transformerless PV inverters could be a guidance to selectappropriate power switching devices in such applications
33 Translated Thermal Loading to Lifetime Based on thethermal model simulations have been carried out in PLECS[43] according to Figure 4 where the system parameters are
4 International Journal of Photoenergy
Power losses Device temp
Electrical domain
Thermal domain
Junction Case Heat-sink Ambient
Pin Poutinvdc
(Ploss = Pin minus Pout)Tj Tc Th Ta
Zth(j-c)Zth(c-h) Zth(h-a)
Figure 5 Coupled relationship between power losses and the junction temperature of the power switching devices 119885th(119895-119888) junction to caseimpedance 119885th(119888-ℎ) case to heat-sink impedance and 119885th(ℎ-119886) heat-sink to ambient impedance
Tc
Tj
Ptot
Ta
Rth1 Rth2 Rth3 Rth4
C1 C2 C3 C4
Ci = 120591iRthiZth(j-c)
Figure 6 Foster model of the junction to case thermal impedance 119885th(119895-119888) shown in Figure 5
Table 2 System parameters for single-phase transformerless grid-connected PV systems
Parameter Symbol Value UnitGrid voltage V
119892RMS 230 VGrid frequency 119891
119892 50 Hz
LCL-filter1198711
36 mH119862119891 235 120583F
1198712
4 mHDamping resistor 119877
11988910 Ω
Switching frequency 119891119904
10 kHzParameters of PV strings (3 strings 15 panels for each string)
at 25∘C and 1 kWm2
Power at MPP 119875MPP 299 kWVoltage at MPP 119881MPP 405 VCurrent at MPP 119868MPP 738 A
shown in Table 2 In order to create the lookup tables forlong-termmission profiles several constant operating condi-tions (eg solar irradiance 08 kWm2 ambient temperature25∘C) have been simulated firstly where a perturb-and-observe maximum power point (MPP) tracking algorithmhas been used [33ndash35 38] Figure 7 exemplifies the simulationmodel for a full-bridge inverter system A proportional reso-nant current controller has been adopted to control the gridcurrent considering power quality requirements [2] Using
the lookup table model the yearly mission profile (Figure 3)has been resampled (5minssample) and translated intothe thermal loading of the corresponding power switchingdevices as it is presented in Figure 8
Although the transformerless PV inverters (both the H6and the HERIC) can maintain a higher efficiency as reportedin the literature in contrast to the FB-Bipolar inverter thethermal loading on those switching devices is unequal as itcan be seen in Figure 8 Specifically the maximum junctiontemperature of the extra devices in an H6 inverter is thehighest indicating high power losses since they are switchedat a high frequency However this is not the case for theHERIC inverter where only one of the extra switchingdevices is switched at the grid frequency during a half cycleTherefore the power losses are lower and thus the thermalloading as it is shown in Figure 8 From the above qualitativeanalysis it is implied that much attention has to be paid onthe extra switching devices in transformerless PV invertersParticularly for theH6 inverter power switching deviceswithlower conduction losses and higher rated maximum junctiontemperature are desirable while the total cost has to be takeninto consideration as well
When the thermal loading profile appearing in the powerswitching devices is available a quantitative prediction ofthe device lifetime under the mission profile is enabled by arain-flow counting algorithm [41 42]The rain-flow countingalgorithm is a quantitative representation of the thermalloading which extracts the temperature information in detailin terms of the mean junction temperature 119879
119895119898 temperature
International Journal of Photoenergy 5
STa
PV++
+++
+
minus
minus
A
CC
A
V VCPVC 11e minus 3
PV
iPV
PWM
1
2 345
Full-bridgeinverter
a
a
b
b
R1 R2L1 L2
Cf GridRd
s
ig
gControl system
Probe
Probe
Probe
Probe
Probe
Probe
Probe
Probe
ProbeVac
Iac
PV V I P
PV P V
AC grid
PV string
P versus V
s
+
minus
f(u)
f(u)
f(u)
f(u)
D1
D2 D4
D3
Heat sink
IGBT1
IGBT2
IGBT3
IGBT4
Scope
Thermal chain T tint
Figure 7 Simulation model of a single-phase full-bridge PV inverter system in PLECS
FB-bipolar
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
S1ndash4
S1ndash4
S1ndash4
1011 0312 0912Time of a year (monthyear)
1011 0312 0912Time of a year (monthyear)
1011 0312 0912Time of a year (monthyear)
H6
Extra devices S56
Extra devices S56
HERIC
(a)
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
S1ndash4
S1ndash4
S1ndash4
Extra devices S56
Extra devices S56
Time of a day (hoursmin)0000 1200 2400
Time of a day (hoursmin)0000 1200 2400
Time of a day (hoursmin)0000 1200 2400
(b)
Figure 8 Translated thermal loading (maximum junction temperature 119879119895max) of the power switching devices of the three different
transformerless grid-connected PV inverters under a yearly mission profile shown in Figure 3 (a) the yearly long-term thermal loadingand (b) details of the maximum junction temperature of the power switching devices in a cloudy day of the year
6 International Journal of Photoenergy
Table 3 Parameters of the lifetime model for power devices [48]
Parameter Value Unit Experimental condition119860 34368 times 1014 mdash120572 minus4923 mdash 64K le Δ119879
119895le 113 K
1205730
1942 mdash 019 le ar le 0421205731
minus9012 times 10minus3 mdash119862 1434 mdash 007 s le 119905
119900119899le 63 s
120574 minus1208 mdash119891119889
06204 mdash119864119886
006606 eV 325∘C le 119879119895119898
le 122∘C119896119861
86173324 times 10minus5 eVK
cycle amplitude 119879119895 cycle period 119905
119900119899 number of cycles n and
so forthThen the extracted temperature information can beused for the lifetime prediction according to a specific lifetimemodel For example a lifetime model of power switchingdevices is introduced in [48] and it can be expressed as
119873119891= 119860Δ119879
120572
119895(119886119903)1205731Δ119879119895+1205730 (
119862 + (119905119900119899)120574
119862 + 1) exp(
119864119886
119896119861119879119895119898
)119891119889
(1)
where119873119891is the number of cycles to fail119891
119889is the diode effect
119886119903 is the bond-wire aspect ratio 119896119861is the Boltzmann constant
119864119886is the activation energy and 119860 120572 120573
0 1205731 120574 and 119862 are
the lifetime model parameters as it is shown in Table 3 Thelifetime model also implies that the junction temperature hasa significant impact on the number of cycles to fail that is thereliability of the power switching devices
According to Minerrsquos rule [24 42 48] the life consump-tion LC the damage due to the thermal stress is the linearlyaccumulative damage from different thermal cycles The LCcan then be expressed as
119871119862 = sum
119894
119899119894
119873119891119894
(2)
in which 119899119894is the number of cycles at the stressΔ119879
119895119894extracted
by the rain-flow counting algorithm and 119873119891119894is the number
of cycles to fail based on (1) Subsequently the lifetime of thepower switching devices can be given as
119871119875=119905119872119875
119871119862(3)
with 119871119875being the predicted lifetime and 119905
119872119875being the
mission profile period (eg a year)Using the above reliability analysis procedure the lifetime
of the power switching devices in the transformerless PVinverters can then be estimated as long as a mission profileand a lifetimemodel of high confidence are available Figure 9summarizes the mission profile based analysis approachwhich can also be used in other power electronics convertersfor example wind turbine converters where the missionprofiles are available
Mission profile
Mission profiletranslation
Thermal loadinginterpretation
Lifetimeprediction
∘C
System models
Loading profilecounting
Lifetimemodels
Counting algorithms
Extracted thermal info
∙ Level crossing∙ Rain-flow∙ Simple range counting∙ middot middot middot
∙ middot middot middot
∙ Tjm-mean junction temp∙ ΔTj-temp cycle amplitude∙ ton -cycle period
Figure 9 Flowchart of the mission profile based reliability analysisapproach for transformerless PV inverters
4 Reliability Assessment
According to Figure 9 the lifetime of the power switchingdevices in the three transformerless PV inverters under theyearly mission profile shown in Figure 3 can be obtained andevaluated In order to benchmark the reliability quantita-tively the thermal loading profiles have to be interpreted firstaccording to (1) and Figure 9 A rain-flow counting algorithmhas been adopted and the results are presented in Figure 10It can be observed in Figure 10 that the additional devicesof the H6 inverter (ie S
5and S
6) have a larger number
of cycles compared to the other power switching devices ofthis topology (S
1sim4) This indicates that the extra devices to
realize an elimination of the leakage currents become themost critical components of the H6 inverter according to(2) and (3) As a consequence more reliable power devicesare preferable as the extra devices when designing an H6based transformerless PV system In the case of the HERICinverter based transformerless PV systems the extra deviceshave a smaller number of cycles compared to those of theH6 inverter Moreover the number of cycles of the otherpower switching devices of theHERC inverter is even smallerthan that of the FB-Bipolar inverter under the same missionprofile This means that the thermal stress on the powerswitching devices of the HERIC inverter is the lowest andthus the HERIC inverter can achieve the highest reliabilityif the same mission profile is applied to those invertercandidates while also maintaining a higher efficiency as itis reported in [12 14] The discussion is in agreement withthe analysis presented in Section 33 based on the translatedthermal loading profiles
It should be noted that the life consumption and thusthe lifetime of the power switching devices according to (2)and (3) can quantitatively be obtained on condition that thelifetime model of (1) and also the parameters given in Table 3are at a high confident level However those parameters are
International Journal of Photoenergy 7
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
(a)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15 minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
S56
S56
(b)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4S56
S56
(c)
Figure 10 Rain-flowing counting results (number of cycles distributions at the cycle amplitude Δ119879119895and the mean junction temperature 119879
119895119898)
of the thermal loading profiles shown in Figure 8 (a) FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
8 International Journal of Photoenergy
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
(a)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
S56
(b)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4S56
(c)
Figure 11 Normalized life consumption (lifetime comparison) of the three transformerless PV inverters under the same mission profile (a)FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
extracted under specific conditions (eg 007 s le 119905119900119899
le
63 s) for the power switching devices introduced in [48]Therefore quantitative prediction errors will be inevitableIn order to reduce the parameter dependency and also thereliability model dependency the life consumption given in(2) is normalized and substituting (1) yields
119871119862 =119871119862
119871119862119887
= (sum
119894
119899119894
(Δ119879119895119894)120572
(119886119903)1205731Δ119879119895119894 [119862 + (119905
119900119899119894)120574] 119890119864119886(119896119861119879119895119898119894))
sdot (sum
119897
119899119897
(Δ1198791015840
119895119897)120572
(119886119903)1205731Δ1198791015840
119895119897 [119862 + (1199051015840
119900119899119897)120574] 119890119864119886(1198961198611198791015840
119895119898119897)
)
minus1
(4)
where 119871119862 is the normalized life consumption and LCb is thebase LC for normalization For example LCb can be chosenas the life consumption of the power switching devices of theFB-Bipolar inverter under the samemission profileThen thepredicted lifetime can be expressed as
119871119901=
1
1198711198621198711015840
119901(5)
in which 1198711015840
119901is the predicted lifetime of the base system used
for normalizationFigure 11 shows the normalized life consumption of the
three transformerless PV inverters according to (4) and thecounting results enabled by a rain-flow algorithm The lifeconsumption of the power switching devices of the FB-Bipolar (ie S
1sim4) is selected as the base life consumption for
normalization in Figure 11 It can be seen in Figure 11 that theextra power switching devices of the H6 inverter consumemuch more life compared to the other devices and also thoseof the HERIC inverter It implies that the degradation of theadditional devices of the H6 inverter happens much fasterand then the entire H6 systemmay fail to operate earlier thanthe other two transformerless PV inverters This comparisonfurther confirms that the HERIC inverter would be the mostpromising solution in terms of reliability
In addition by comparing the rain-flow counting resultsshown in Figure 10 with the normalized life consumptionshown in Figure 11 one interesting conclusion can be drawnwhich is that although there are a few cycles of a largetemperature cycling amplitude (eg ten cycles of 55∘C to65∘C for the extra devices S
56of the H6 inverter) they do
contribute much more damage (eg 04 in Figure 11(b))when the lifetime model of (1) is adopted Large cyclingamplitude is mainly induced by the mission profile whichconfirms that the mission profile effect has to be taken intoaccount in a reliability-oriented design of power electronics
International Journal of Photoenergy 9
converters In a word the reliability assessment in this paperreveals that much attention has to be put on the thermaldesign of the critical components in an entire PV inverter inorder to reduce the cost of energy
5 Conclusions
In this paper a qualitative reliability assessment of threeselected single-phase transformerless PV inverters has beencarried out in accordance with a mission profile based reli-ability analysis approach A real-field yearly mission profilehas been applied to the selected transformerless candidatesfor the reliability assessment The comparison results haverevealed that although minimizing leakage currents as wellas maintaining a satisfactory efficiency has been targetedby those inverters the extra devices that are used fordisconnection of the PV panels or the PV inverters mightbe heated up during operation The high thermal loadingwill further induce failures of the power switching devicesbeing a big challenge to the entire system reliability As aconsequence many efforts should be devoted to a reliability-oriented design of the critical components in a PV inverterand thus a reduced cost of energy can be achieved
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F Blaabjerg K Ma and Y Yang ldquoPower electronicsmdashthe keytechnology for renewable energy systemsrdquo in Proceedings ofthe 9th International Conference on Ecological Vehicles andRenewable Energies (EVER rsquo14) pp 1ndash11 Monte-Carlo MonacoMarch 2014
[2] 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
[3] J M Carrasco L G Franquelo J T Bialasiewicz et al ldquoPower-electronic systems for the grid integration of renewable energysources a surveyrdquo IEEE Transactions on Industrial Electronicsvol 53 no 4 pp 1002ndash1016 2006
[4] J D vanWyk and F C Lee ldquoOn a future for power electronicsrdquoIEEE Journal of Emerging and Selected Topics in Power Electron-ics vol 1 no 2 pp 59ndash72 2013
[5] A Golnas ldquoPV system reliability an operatorrsquos perspectiverdquoIEEE Journal of Photovoltaics vol 3 no 1 pp 416ndash421 2013
[6] A Ristow M Begovic A Pregelj and A Rohatgi ldquoDevelop-ment of a methodology for improving photovoltaic inverterreliabilityrdquo IEEE Transactions on Industrial Electronics vol 55no 7 pp 2581ndash2592 2008
[7] E Romero-Cadaval G Spagnuolo L G Franquelo C ARamos-Paja T Suntio and W M Xiao ldquoGrid-connectedphotovoltaic generation plants components and operationrdquoIEEE Industrial ElectronicsMagazine vol 7 no 3 pp 6ndash20 2013
[8] REN21 ldquoRenewables 2014 global status reportrdquo Tech Rep 2014httpwwwren21net
[9] M Liserre T Sauter and J Y Hung ldquoFuture energy systemsintegrating renewable energy sources into the smart power
grid through industrial electronicsrdquo IEEE Industrial ElectronicsMagazine vol 4 no 1 pp 18ndash37 2010
[10] C-L Shen and S-H Yang ldquoMulti-input converter with MPPTfeature for wind-PV power generation systemrdquo InternationalJournal of Photoenergy vol 2013 Article ID 129254 13 pages2013
[11] F Blaabjerg and K Ma ldquoFuture on power electronics for windturbine systemsrdquo IEEE Journal of Emerging and Selected Topicsin Power Electronics vol 1 no 3 pp 139ndash152 2013
[12] R TeodorescuM Liserre and P RodriguezGrid Converters forPhotovoltaic and Wind Power Systems Wiley-IEEE Press 2011
[13] R Gonzalez J Lopez P Sanchis and L Marroyo ldquoTrans-formerless inverter for single-phase photovoltaic systemsrdquo IEEETransactions on Power Electronics vol 22 no 2 pp 693ndash6972007
[14] H Schmidt C Siedle and J Ketterer ldquoDCAC converter toconvert direct electric voltage into alternating voltage or intoalternating currentrdquo US Patent 7046534 2006
[15] T Kerekes M Liserre R Teodorescu C Klumpner and MSumner ldquoEvaluation of three-phase transformerless photo-voltaic inverter topologiesrdquo IEEE Transactions on Power Elec-tronics vol 24 no 9 pp 2202ndash2211 2009
[16] R Gonzalez E Gubıa J Lopez and L Marroyo ldquoTransformer-less single-phase multilevel-based photovoltaic inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 7 pp 2694ndash2702 2008
[17] Advanced Energy ldquoWhatrsquos ahead for PV inverter technologyrdquoGreentechsolar 2014 httpwwwgreentechmediacom
[18] I Patrao E Figueres F Gonzalez-Espın and G GarceraldquoTransformerless topologies for grid-connected single-phasephotovoltaic invertersrdquo Renewable and Sustainable EnergyReviews vol 15 no 7 pp 3423ndash3431 2011
[19] N Achilladelis E Koutroulis and F Blaabjerg ldquoOptimizedpulse width modulation for transformerless active-NPC invert-ersrdquo in Proceedings of the 16th European Conference on PowerElectronics and Applications (EPE rsquo14-ECCE Europe) pp 1ndash10Lappeenranta Finland August 2014
[20] S Saridakis E Koutroulis and F Blaabjerg ldquoOptimal design ofmodern transformerless PV inverter topologiesdrdquo IEEE Trans-actions on Energy Conversion vol 28 no 2 pp 394ndash404 2013
[21] Y Yang H Wang F Blaabjerg and K Ma ldquoMission profilebased multi-disciplinary analysis of power modules in single-phase transformerless photovoltaic invertersrdquo in Proceedingsof the 15th European Conference on Power Electronics andApplications (EPE rsquo13) pp 1ndash10 IEEE Lille France September2013
[22] S E de Leon-Aldaco H Calleja F Chan and H R Jimenez-Grajales ldquoEffect of the mission profile on the reliability of apower converter aimed at photovoltaic applicationsmdasha casestudyrdquo IEEE Transactions on Power Electronics vol 28 no 6pp 2998ndash3007 2013
[23] H Wang M Liserre and F Blaabjerg ldquoToward reliable powerelectronics challenges design tools and opportunitiesrdquo IEEEIndustrial Electronics Magazine vol 7 no 2 pp 17ndash26 2013
[24] H Huang and P A Mawby ldquoA lifetime estimation techniquefor voltage source invertersrdquo IEEE Transactions on PowerElectronics vol 28 no 8 pp 4113ndash4119 2013
[25] P McCluskey ldquoReliability of power electronics under thermalloadingrdquo in Proceedings of the 7th International Conference onIntegrated Power Electronics Systems (CIPS rsquo12) March 2012
10 International Journal of Photoenergy
[26] H Lu C Bailey and C Yin ldquoDesign for reliability of powerelectronics modulesrdquoMicroelectronics Reliability vol 49 no 9ndash11 pp 1250ndash1255 2009
[27] M Ciappa ldquoLifetime prediction on the base ofmission profilesrdquoMicroelectronics Reliability vol 45 no 9-11 pp 1293ndash1298 2005
[28] F Chan and H Calleja ldquoReliability estimation of three single-phase topologies in grid-connected PV systemsrdquo IEEE Trans-actions on Industrial Electronics vol 58 no 7 pp 2683ndash26892011
[29] K Ma M Liserre F Blaabjerg and T Kerekes ldquoThermalloading and lifetime estimation for power device consideringmission profiles in wind power converterrdquo IEEE Transactionson Power Electronics vol 30 no 2 pp 590ndash602 2015
[30] S Harb and R S Balog ldquoReliability of candidate pho-tovoltaic module-integrated-inverter (PV-MII) topologiesmdashausagemodel approachrdquo IEEE Transactions on Power Electronicsvol 28 no 6 pp 3019ndash3027 2013
[31] P Zhang YWangW Xiao andW Li ldquoReliability evaluation ofgrid-connected photovoltaic power systemsrdquo IEEETransactionson Sustainable Energy vol 3 no 3 pp 379ndash389 2012
[32] S E De Leon-Aldaco H Calleja and J Aguayo ldquoReliability andmission profiles of photovoltaic systems a FIDES approachrdquoIEEE Transactions on Power Electronics vol 30 no 5 pp 2578ndash2586 2015
[33] S B Kjaer J K Pedersen and F Blaabjerg ldquoA review of single-phase grid-connected inverters for photovoltaicmodulesrdquo IEEETransactions on Industry Applications vol 41 no 5 pp 1292ndash1306 2005
[34] H Li J PengW Liu Z Huang andK-C Lin ldquoA newton-basedextremumseekingMPPTmethod for photovoltaic systemswithstochastic perturbationsrdquo International Journal of Photoenergyvol 2014 Article ID 938526 13 pages 2014
[35] D Sera L Mathe T Kerekes S V Spataru and R TeodoresculdquoOn the perturb-and-observe and incremental conductancemppt methods for PV systemsrdquo IEEE Journal of Photovoltaicsvol 3 no 3 pp 1070ndash1078 2013
[36] M Abdulkadir A H M Yatim and S T Yusuf ldquoAn improvedPSO-based MPPT control strategy for photovoltaic systemsrdquoInternational Journal of Photoenergy vol 2014 Article ID818232 11 pages 2014
[37] Y Zhou and H Li ldquoAnalysis and suppression of leakage cur-rent in cascaded-multilevel-inverter-based PV systemsrdquo IEEETransactions on Power Electronics vol 29 no 10 pp 5265ndash52772014
[38] A Hajiah T Khatib K Sopian and M Sebzali ldquoPerformanceof grid-connected photovoltaic system in two sites in KuwaitrdquoInternational Journal of Photoenergy vol 2012 Article ID178175 7 pages 2012
[39] M Musallam C Yin C Bailey and M Johnson ldquoMissionprofile-based reliability design and real-time life consumptionestimation in power electronicsrdquo IEEE Transactions on PowerElectronics vol 30 no 5 pp 2601ndash2613 2015
[40] Y Yang HWang F Blaabjerg and T Kerekes ldquoA hybrid powercontrol concept for PV inverters with reduced thermal loadingrdquoIEEE Transactions on Power Electronics vol 29 no 12 pp 6271ndash6275 2014
[41] A T Bryant P A Mawby P R Palmer E Santi and J LHudgins ldquoExploration of power device reliability using com-pact device models and fast electrothermal simulationrdquo IEEETransactions on Industry Applications vol 44 no 3 pp 894ndash903 2008
[42] M Musallam and C M Johnson ldquoAn efficient implementationof the rainflow counting algorithm for life consumption estima-tionrdquo IEEE Transactions on Reliability vol 61 no 4 pp 978ndash986 2012
[43] Plexim Gmbh ldquoPLECSmdashthe simulation platform for powerelectronics systemsrdquo Workshop Documentation 1 Aalborg2014
[44] I F Kovacevic U Drofenik and J W Kolar ldquoNew physicalmodel for lifetime estimation of powermodulesrdquo in Proceedingsof the International Power Electronics Conference (IPEC rsquo10) pp2106ndash2114 Sapporo Japan June 2010
[45] C Busca R Teodorescu F Blaabjerg et al ldquoAn overview ofthe reliability prediction related aspects of high power IGBTsin wind power applicationsrdquoMicroelectronics Reliability vol 51no 9ndash11 pp 1903ndash1907 2011
[46] ABB ldquoApplication NotemdashApplying IGBTsrdquo 2014 httpwwwabbcom
[47] A Volke and M Hornkamp IGBT ModulesmdashTechnologiesDriver and Application Infineon Technologies AG MunichGermany 2012
[48] U Scheuermann ldquoReliability of advanced power modules forextended maximum junction temperaturesrdquo Bodorsquos Power Sys-tems pp 26ndash30 2014
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 3
PV stringsmodules Full-bridgeiPV
CPV1
CPV2
CP
LCL-filter
DC path
Grid∘C
OSola
r irr
adia
nce
Am
bien
t tem
pera
ture
Cf
S1
S2
S3
S4
S5
S6
D3
D2
D1
D6
D5
D4
D8
D7L1 L2
A
B
(a)
PV stringsmodules Full-bridge
iPV
CPV
CP
LCL-filter
AC path
Grid∘C
OSola
r irr
adia
nce
Am
bien
t tem
pera
ture
Cf
S1
S2
S3
S4
S5
S6
D3
D2
D1
D6
D5
D4
L1 L2A
B
(b)
Figure 2 Examples of single-phase transformerless PV inverters derived from the single-phase full-bridge topology by adding extra powerswitching devices (a) H6 inverter [13] and (b) HERIC inverter [14]
Sola
r irr
adia
nce (
kWm
2)
15
10
05
0Oct Nov Dec Jan Feb Mar Apr Jun Jul Aug SepMay
(a)
Am
bien
t tem
p (∘
C)
40
20
0
minus20Oct Nov Dec Jan Feb Mar Apr Jun Jul Aug SepMay
(b)
Figure 3 A yearly mission profile used for the selected transformerless PV inverters (1 secsample) (a) solar irradiance and (b) ambienttemperature
∘C
MPPTMiss
ion
profi
le GridElectricalsystem
PVmodels
PinPout
PlossTransformerlessPV inverters
(electrical andloss models)
TjTj
Thermalmodel
Thermalloading profile
(a)
∘C
Lookup tablebased
simulation (thermal) model
Miss
ion
profi
le
Tj Thermalloading profile
(b)
Figure 4 Approach of the mission profile translation to thermal loading at different time scales (MPPT maximum power point tracking 119879119895
junction temperature of the power devices) (a) short-term mission profiles and (b) long-term mission profiles
32 Thermal Modelling of Power Switching Devices As it isshown in Figure 4 the translation from a mission profileto the corresponding thermal loading profile requires athermalmodel which links the electrical performance (powerlosses 119875loss) and the thermal behavior (junction temperature119879119895) The coupled relationship is demonstrated in Figure 5
in a FB PV inverter system which shows that the powerlosses on the switching devices will introduce a temperaturerise due to the thermal impedance in the power switchingdevices The thermal impedance can be modeled as a Fostermodel [43ndash47] as it is shown in Figure 6 Details of thethermal modelling of power semiconductors can be found in[46 47]
Typically for such a model of the thermal impedance theparameter data is provided in the datasheet Table 1 showsthe thermal parameters of the power switching device froma leading manufacturer used in the paper Notably all thedevices are the same in the three transformerless PV invertersfor comparison in terms of thermal loading and thus thebenchmarking results indicating the critical components of
Table 1Thermal impedance parameters of power switching devicesfrom a leading manufacturer according to Figure 6
Impedance 119885th(119895-119888)
119894 1 2 3 4IGBT119877th119894 (KW) 0074 0173 0526 0527120591119894(s) 00005 0005 005 02
Diode119877th119894 (KW) 0123 0264 0594 0468120591119894(s) 00005 0005 005 02
transformerless PV inverters could be a guidance to selectappropriate power switching devices in such applications
33 Translated Thermal Loading to Lifetime Based on thethermal model simulations have been carried out in PLECS[43] according to Figure 4 where the system parameters are
4 International Journal of Photoenergy
Power losses Device temp
Electrical domain
Thermal domain
Junction Case Heat-sink Ambient
Pin Poutinvdc
(Ploss = Pin minus Pout)Tj Tc Th Ta
Zth(j-c)Zth(c-h) Zth(h-a)
Figure 5 Coupled relationship between power losses and the junction temperature of the power switching devices 119885th(119895-119888) junction to caseimpedance 119885th(119888-ℎ) case to heat-sink impedance and 119885th(ℎ-119886) heat-sink to ambient impedance
Tc
Tj
Ptot
Ta
Rth1 Rth2 Rth3 Rth4
C1 C2 C3 C4
Ci = 120591iRthiZth(j-c)
Figure 6 Foster model of the junction to case thermal impedance 119885th(119895-119888) shown in Figure 5
Table 2 System parameters for single-phase transformerless grid-connected PV systems
Parameter Symbol Value UnitGrid voltage V
119892RMS 230 VGrid frequency 119891
119892 50 Hz
LCL-filter1198711
36 mH119862119891 235 120583F
1198712
4 mHDamping resistor 119877
11988910 Ω
Switching frequency 119891119904
10 kHzParameters of PV strings (3 strings 15 panels for each string)
at 25∘C and 1 kWm2
Power at MPP 119875MPP 299 kWVoltage at MPP 119881MPP 405 VCurrent at MPP 119868MPP 738 A
shown in Table 2 In order to create the lookup tables forlong-termmission profiles several constant operating condi-tions (eg solar irradiance 08 kWm2 ambient temperature25∘C) have been simulated firstly where a perturb-and-observe maximum power point (MPP) tracking algorithmhas been used [33ndash35 38] Figure 7 exemplifies the simulationmodel for a full-bridge inverter system A proportional reso-nant current controller has been adopted to control the gridcurrent considering power quality requirements [2] Using
the lookup table model the yearly mission profile (Figure 3)has been resampled (5minssample) and translated intothe thermal loading of the corresponding power switchingdevices as it is presented in Figure 8
Although the transformerless PV inverters (both the H6and the HERIC) can maintain a higher efficiency as reportedin the literature in contrast to the FB-Bipolar inverter thethermal loading on those switching devices is unequal as itcan be seen in Figure 8 Specifically the maximum junctiontemperature of the extra devices in an H6 inverter is thehighest indicating high power losses since they are switchedat a high frequency However this is not the case for theHERIC inverter where only one of the extra switchingdevices is switched at the grid frequency during a half cycleTherefore the power losses are lower and thus the thermalloading as it is shown in Figure 8 From the above qualitativeanalysis it is implied that much attention has to be paid onthe extra switching devices in transformerless PV invertersParticularly for theH6 inverter power switching deviceswithlower conduction losses and higher rated maximum junctiontemperature are desirable while the total cost has to be takeninto consideration as well
When the thermal loading profile appearing in the powerswitching devices is available a quantitative prediction ofthe device lifetime under the mission profile is enabled by arain-flow counting algorithm [41 42]The rain-flow countingalgorithm is a quantitative representation of the thermalloading which extracts the temperature information in detailin terms of the mean junction temperature 119879
119895119898 temperature
International Journal of Photoenergy 5
STa
PV++
+++
+
minus
minus
A
CC
A
V VCPVC 11e minus 3
PV
iPV
PWM
1
2 345
Full-bridgeinverter
a
a
b
b
R1 R2L1 L2
Cf GridRd
s
ig
gControl system
Probe
Probe
Probe
Probe
Probe
Probe
Probe
Probe
ProbeVac
Iac
PV V I P
PV P V
AC grid
PV string
P versus V
s
+
minus
f(u)
f(u)
f(u)
f(u)
D1
D2 D4
D3
Heat sink
IGBT1
IGBT2
IGBT3
IGBT4
Scope
Thermal chain T tint
Figure 7 Simulation model of a single-phase full-bridge PV inverter system in PLECS
FB-bipolar
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
S1ndash4
S1ndash4
S1ndash4
1011 0312 0912Time of a year (monthyear)
1011 0312 0912Time of a year (monthyear)
1011 0312 0912Time of a year (monthyear)
H6
Extra devices S56
Extra devices S56
HERIC
(a)
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
S1ndash4
S1ndash4
S1ndash4
Extra devices S56
Extra devices S56
Time of a day (hoursmin)0000 1200 2400
Time of a day (hoursmin)0000 1200 2400
Time of a day (hoursmin)0000 1200 2400
(b)
Figure 8 Translated thermal loading (maximum junction temperature 119879119895max) of the power switching devices of the three different
transformerless grid-connected PV inverters under a yearly mission profile shown in Figure 3 (a) the yearly long-term thermal loadingand (b) details of the maximum junction temperature of the power switching devices in a cloudy day of the year
6 International Journal of Photoenergy
Table 3 Parameters of the lifetime model for power devices [48]
Parameter Value Unit Experimental condition119860 34368 times 1014 mdash120572 minus4923 mdash 64K le Δ119879
119895le 113 K
1205730
1942 mdash 019 le ar le 0421205731
minus9012 times 10minus3 mdash119862 1434 mdash 007 s le 119905
119900119899le 63 s
120574 minus1208 mdash119891119889
06204 mdash119864119886
006606 eV 325∘C le 119879119895119898
le 122∘C119896119861
86173324 times 10minus5 eVK
cycle amplitude 119879119895 cycle period 119905
119900119899 number of cycles n and
so forthThen the extracted temperature information can beused for the lifetime prediction according to a specific lifetimemodel For example a lifetime model of power switchingdevices is introduced in [48] and it can be expressed as
119873119891= 119860Δ119879
120572
119895(119886119903)1205731Δ119879119895+1205730 (
119862 + (119905119900119899)120574
119862 + 1) exp(
119864119886
119896119861119879119895119898
)119891119889
(1)
where119873119891is the number of cycles to fail119891
119889is the diode effect
119886119903 is the bond-wire aspect ratio 119896119861is the Boltzmann constant
119864119886is the activation energy and 119860 120572 120573
0 1205731 120574 and 119862 are
the lifetime model parameters as it is shown in Table 3 Thelifetime model also implies that the junction temperature hasa significant impact on the number of cycles to fail that is thereliability of the power switching devices
According to Minerrsquos rule [24 42 48] the life consump-tion LC the damage due to the thermal stress is the linearlyaccumulative damage from different thermal cycles The LCcan then be expressed as
119871119862 = sum
119894
119899119894
119873119891119894
(2)
in which 119899119894is the number of cycles at the stressΔ119879
119895119894extracted
by the rain-flow counting algorithm and 119873119891119894is the number
of cycles to fail based on (1) Subsequently the lifetime of thepower switching devices can be given as
119871119875=119905119872119875
119871119862(3)
with 119871119875being the predicted lifetime and 119905
119872119875being the
mission profile period (eg a year)Using the above reliability analysis procedure the lifetime
of the power switching devices in the transformerless PVinverters can then be estimated as long as a mission profileand a lifetimemodel of high confidence are available Figure 9summarizes the mission profile based analysis approachwhich can also be used in other power electronics convertersfor example wind turbine converters where the missionprofiles are available
Mission profile
Mission profiletranslation
Thermal loadinginterpretation
Lifetimeprediction
∘C
System models
Loading profilecounting
Lifetimemodels
Counting algorithms
Extracted thermal info
∙ Level crossing∙ Rain-flow∙ Simple range counting∙ middot middot middot
∙ middot middot middot
∙ Tjm-mean junction temp∙ ΔTj-temp cycle amplitude∙ ton -cycle period
Figure 9 Flowchart of the mission profile based reliability analysisapproach for transformerless PV inverters
4 Reliability Assessment
According to Figure 9 the lifetime of the power switchingdevices in the three transformerless PV inverters under theyearly mission profile shown in Figure 3 can be obtained andevaluated In order to benchmark the reliability quantita-tively the thermal loading profiles have to be interpreted firstaccording to (1) and Figure 9 A rain-flow counting algorithmhas been adopted and the results are presented in Figure 10It can be observed in Figure 10 that the additional devicesof the H6 inverter (ie S
5and S
6) have a larger number
of cycles compared to the other power switching devices ofthis topology (S
1sim4) This indicates that the extra devices to
realize an elimination of the leakage currents become themost critical components of the H6 inverter according to(2) and (3) As a consequence more reliable power devicesare preferable as the extra devices when designing an H6based transformerless PV system In the case of the HERICinverter based transformerless PV systems the extra deviceshave a smaller number of cycles compared to those of theH6 inverter Moreover the number of cycles of the otherpower switching devices of theHERC inverter is even smallerthan that of the FB-Bipolar inverter under the same missionprofile This means that the thermal stress on the powerswitching devices of the HERIC inverter is the lowest andthus the HERIC inverter can achieve the highest reliabilityif the same mission profile is applied to those invertercandidates while also maintaining a higher efficiency as itis reported in [12 14] The discussion is in agreement withthe analysis presented in Section 33 based on the translatedthermal loading profiles
It should be noted that the life consumption and thusthe lifetime of the power switching devices according to (2)and (3) can quantitatively be obtained on condition that thelifetime model of (1) and also the parameters given in Table 3are at a high confident level However those parameters are
International Journal of Photoenergy 7
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
(a)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15 minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
S56
S56
(b)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4S56
S56
(c)
Figure 10 Rain-flowing counting results (number of cycles distributions at the cycle amplitude Δ119879119895and the mean junction temperature 119879
119895119898)
of the thermal loading profiles shown in Figure 8 (a) FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
8 International Journal of Photoenergy
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
(a)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
S56
(b)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4S56
(c)
Figure 11 Normalized life consumption (lifetime comparison) of the three transformerless PV inverters under the same mission profile (a)FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
extracted under specific conditions (eg 007 s le 119905119900119899
le
63 s) for the power switching devices introduced in [48]Therefore quantitative prediction errors will be inevitableIn order to reduce the parameter dependency and also thereliability model dependency the life consumption given in(2) is normalized and substituting (1) yields
119871119862 =119871119862
119871119862119887
= (sum
119894
119899119894
(Δ119879119895119894)120572
(119886119903)1205731Δ119879119895119894 [119862 + (119905
119900119899119894)120574] 119890119864119886(119896119861119879119895119898119894))
sdot (sum
119897
119899119897
(Δ1198791015840
119895119897)120572
(119886119903)1205731Δ1198791015840
119895119897 [119862 + (1199051015840
119900119899119897)120574] 119890119864119886(1198961198611198791015840
119895119898119897)
)
minus1
(4)
where 119871119862 is the normalized life consumption and LCb is thebase LC for normalization For example LCb can be chosenas the life consumption of the power switching devices of theFB-Bipolar inverter under the samemission profileThen thepredicted lifetime can be expressed as
119871119901=
1
1198711198621198711015840
119901(5)
in which 1198711015840
119901is the predicted lifetime of the base system used
for normalizationFigure 11 shows the normalized life consumption of the
three transformerless PV inverters according to (4) and thecounting results enabled by a rain-flow algorithm The lifeconsumption of the power switching devices of the FB-Bipolar (ie S
1sim4) is selected as the base life consumption for
normalization in Figure 11 It can be seen in Figure 11 that theextra power switching devices of the H6 inverter consumemuch more life compared to the other devices and also thoseof the HERIC inverter It implies that the degradation of theadditional devices of the H6 inverter happens much fasterand then the entire H6 systemmay fail to operate earlier thanthe other two transformerless PV inverters This comparisonfurther confirms that the HERIC inverter would be the mostpromising solution in terms of reliability
In addition by comparing the rain-flow counting resultsshown in Figure 10 with the normalized life consumptionshown in Figure 11 one interesting conclusion can be drawnwhich is that although there are a few cycles of a largetemperature cycling amplitude (eg ten cycles of 55∘C to65∘C for the extra devices S
56of the H6 inverter) they do
contribute much more damage (eg 04 in Figure 11(b))when the lifetime model of (1) is adopted Large cyclingamplitude is mainly induced by the mission profile whichconfirms that the mission profile effect has to be taken intoaccount in a reliability-oriented design of power electronics
International Journal of Photoenergy 9
converters In a word the reliability assessment in this paperreveals that much attention has to be put on the thermaldesign of the critical components in an entire PV inverter inorder to reduce the cost of energy
5 Conclusions
In this paper a qualitative reliability assessment of threeselected single-phase transformerless PV inverters has beencarried out in accordance with a mission profile based reli-ability analysis approach A real-field yearly mission profilehas been applied to the selected transformerless candidatesfor the reliability assessment The comparison results haverevealed that although minimizing leakage currents as wellas maintaining a satisfactory efficiency has been targetedby those inverters the extra devices that are used fordisconnection of the PV panels or the PV inverters mightbe heated up during operation The high thermal loadingwill further induce failures of the power switching devicesbeing a big challenge to the entire system reliability As aconsequence many efforts should be devoted to a reliability-oriented design of the critical components in a PV inverterand thus a reduced cost of energy can be achieved
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F Blaabjerg K Ma and Y Yang ldquoPower electronicsmdashthe keytechnology for renewable energy systemsrdquo in Proceedings ofthe 9th International Conference on Ecological Vehicles andRenewable Energies (EVER rsquo14) pp 1ndash11 Monte-Carlo MonacoMarch 2014
[2] 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
[3] J M Carrasco L G Franquelo J T Bialasiewicz et al ldquoPower-electronic systems for the grid integration of renewable energysources a surveyrdquo IEEE Transactions on Industrial Electronicsvol 53 no 4 pp 1002ndash1016 2006
[4] J D vanWyk and F C Lee ldquoOn a future for power electronicsrdquoIEEE Journal of Emerging and Selected Topics in Power Electron-ics vol 1 no 2 pp 59ndash72 2013
[5] A Golnas ldquoPV system reliability an operatorrsquos perspectiverdquoIEEE Journal of Photovoltaics vol 3 no 1 pp 416ndash421 2013
[6] A Ristow M Begovic A Pregelj and A Rohatgi ldquoDevelop-ment of a methodology for improving photovoltaic inverterreliabilityrdquo IEEE Transactions on Industrial Electronics vol 55no 7 pp 2581ndash2592 2008
[7] E Romero-Cadaval G Spagnuolo L G Franquelo C ARamos-Paja T Suntio and W M Xiao ldquoGrid-connectedphotovoltaic generation plants components and operationrdquoIEEE Industrial ElectronicsMagazine vol 7 no 3 pp 6ndash20 2013
[8] REN21 ldquoRenewables 2014 global status reportrdquo Tech Rep 2014httpwwwren21net
[9] M Liserre T Sauter and J Y Hung ldquoFuture energy systemsintegrating renewable energy sources into the smart power
grid through industrial electronicsrdquo IEEE Industrial ElectronicsMagazine vol 4 no 1 pp 18ndash37 2010
[10] C-L Shen and S-H Yang ldquoMulti-input converter with MPPTfeature for wind-PV power generation systemrdquo InternationalJournal of Photoenergy vol 2013 Article ID 129254 13 pages2013
[11] F Blaabjerg and K Ma ldquoFuture on power electronics for windturbine systemsrdquo IEEE Journal of Emerging and Selected Topicsin Power Electronics vol 1 no 3 pp 139ndash152 2013
[12] R TeodorescuM Liserre and P RodriguezGrid Converters forPhotovoltaic and Wind Power Systems Wiley-IEEE Press 2011
[13] R Gonzalez J Lopez P Sanchis and L Marroyo ldquoTrans-formerless inverter for single-phase photovoltaic systemsrdquo IEEETransactions on Power Electronics vol 22 no 2 pp 693ndash6972007
[14] H Schmidt C Siedle and J Ketterer ldquoDCAC converter toconvert direct electric voltage into alternating voltage or intoalternating currentrdquo US Patent 7046534 2006
[15] T Kerekes M Liserre R Teodorescu C Klumpner and MSumner ldquoEvaluation of three-phase transformerless photo-voltaic inverter topologiesrdquo IEEE Transactions on Power Elec-tronics vol 24 no 9 pp 2202ndash2211 2009
[16] R Gonzalez E Gubıa J Lopez and L Marroyo ldquoTransformer-less single-phase multilevel-based photovoltaic inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 7 pp 2694ndash2702 2008
[17] Advanced Energy ldquoWhatrsquos ahead for PV inverter technologyrdquoGreentechsolar 2014 httpwwwgreentechmediacom
[18] I Patrao E Figueres F Gonzalez-Espın and G GarceraldquoTransformerless topologies for grid-connected single-phasephotovoltaic invertersrdquo Renewable and Sustainable EnergyReviews vol 15 no 7 pp 3423ndash3431 2011
[19] N Achilladelis E Koutroulis and F Blaabjerg ldquoOptimizedpulse width modulation for transformerless active-NPC invert-ersrdquo in Proceedings of the 16th European Conference on PowerElectronics and Applications (EPE rsquo14-ECCE Europe) pp 1ndash10Lappeenranta Finland August 2014
[20] S Saridakis E Koutroulis and F Blaabjerg ldquoOptimal design ofmodern transformerless PV inverter topologiesdrdquo IEEE Trans-actions on Energy Conversion vol 28 no 2 pp 394ndash404 2013
[21] Y Yang H Wang F Blaabjerg and K Ma ldquoMission profilebased multi-disciplinary analysis of power modules in single-phase transformerless photovoltaic invertersrdquo in Proceedingsof the 15th European Conference on Power Electronics andApplications (EPE rsquo13) pp 1ndash10 IEEE Lille France September2013
[22] S E de Leon-Aldaco H Calleja F Chan and H R Jimenez-Grajales ldquoEffect of the mission profile on the reliability of apower converter aimed at photovoltaic applicationsmdasha casestudyrdquo IEEE Transactions on Power Electronics vol 28 no 6pp 2998ndash3007 2013
[23] H Wang M Liserre and F Blaabjerg ldquoToward reliable powerelectronics challenges design tools and opportunitiesrdquo IEEEIndustrial Electronics Magazine vol 7 no 2 pp 17ndash26 2013
[24] H Huang and P A Mawby ldquoA lifetime estimation techniquefor voltage source invertersrdquo IEEE Transactions on PowerElectronics vol 28 no 8 pp 4113ndash4119 2013
[25] P McCluskey ldquoReliability of power electronics under thermalloadingrdquo in Proceedings of the 7th International Conference onIntegrated Power Electronics Systems (CIPS rsquo12) March 2012
10 International Journal of Photoenergy
[26] H Lu C Bailey and C Yin ldquoDesign for reliability of powerelectronics modulesrdquoMicroelectronics Reliability vol 49 no 9ndash11 pp 1250ndash1255 2009
[27] M Ciappa ldquoLifetime prediction on the base ofmission profilesrdquoMicroelectronics Reliability vol 45 no 9-11 pp 1293ndash1298 2005
[28] F Chan and H Calleja ldquoReliability estimation of three single-phase topologies in grid-connected PV systemsrdquo IEEE Trans-actions on Industrial Electronics vol 58 no 7 pp 2683ndash26892011
[29] K Ma M Liserre F Blaabjerg and T Kerekes ldquoThermalloading and lifetime estimation for power device consideringmission profiles in wind power converterrdquo IEEE Transactionson Power Electronics vol 30 no 2 pp 590ndash602 2015
[30] S Harb and R S Balog ldquoReliability of candidate pho-tovoltaic module-integrated-inverter (PV-MII) topologiesmdashausagemodel approachrdquo IEEE Transactions on Power Electronicsvol 28 no 6 pp 3019ndash3027 2013
[31] P Zhang YWangW Xiao andW Li ldquoReliability evaluation ofgrid-connected photovoltaic power systemsrdquo IEEETransactionson Sustainable Energy vol 3 no 3 pp 379ndash389 2012
[32] S E De Leon-Aldaco H Calleja and J Aguayo ldquoReliability andmission profiles of photovoltaic systems a FIDES approachrdquoIEEE Transactions on Power Electronics vol 30 no 5 pp 2578ndash2586 2015
[33] S B Kjaer J K Pedersen and F Blaabjerg ldquoA review of single-phase grid-connected inverters for photovoltaicmodulesrdquo IEEETransactions on Industry Applications vol 41 no 5 pp 1292ndash1306 2005
[34] H Li J PengW Liu Z Huang andK-C Lin ldquoA newton-basedextremumseekingMPPTmethod for photovoltaic systemswithstochastic perturbationsrdquo International Journal of Photoenergyvol 2014 Article ID 938526 13 pages 2014
[35] D Sera L Mathe T Kerekes S V Spataru and R TeodoresculdquoOn the perturb-and-observe and incremental conductancemppt methods for PV systemsrdquo IEEE Journal of Photovoltaicsvol 3 no 3 pp 1070ndash1078 2013
[36] M Abdulkadir A H M Yatim and S T Yusuf ldquoAn improvedPSO-based MPPT control strategy for photovoltaic systemsrdquoInternational Journal of Photoenergy vol 2014 Article ID818232 11 pages 2014
[37] Y Zhou and H Li ldquoAnalysis and suppression of leakage cur-rent in cascaded-multilevel-inverter-based PV systemsrdquo IEEETransactions on Power Electronics vol 29 no 10 pp 5265ndash52772014
[38] A Hajiah T Khatib K Sopian and M Sebzali ldquoPerformanceof grid-connected photovoltaic system in two sites in KuwaitrdquoInternational Journal of Photoenergy vol 2012 Article ID178175 7 pages 2012
[39] M Musallam C Yin C Bailey and M Johnson ldquoMissionprofile-based reliability design and real-time life consumptionestimation in power electronicsrdquo IEEE Transactions on PowerElectronics vol 30 no 5 pp 2601ndash2613 2015
[40] Y Yang HWang F Blaabjerg and T Kerekes ldquoA hybrid powercontrol concept for PV inverters with reduced thermal loadingrdquoIEEE Transactions on Power Electronics vol 29 no 12 pp 6271ndash6275 2014
[41] A T Bryant P A Mawby P R Palmer E Santi and J LHudgins ldquoExploration of power device reliability using com-pact device models and fast electrothermal simulationrdquo IEEETransactions on Industry Applications vol 44 no 3 pp 894ndash903 2008
[42] M Musallam and C M Johnson ldquoAn efficient implementationof the rainflow counting algorithm for life consumption estima-tionrdquo IEEE Transactions on Reliability vol 61 no 4 pp 978ndash986 2012
[43] Plexim Gmbh ldquoPLECSmdashthe simulation platform for powerelectronics systemsrdquo Workshop Documentation 1 Aalborg2014
[44] I F Kovacevic U Drofenik and J W Kolar ldquoNew physicalmodel for lifetime estimation of powermodulesrdquo in Proceedingsof the International Power Electronics Conference (IPEC rsquo10) pp2106ndash2114 Sapporo Japan June 2010
[45] C Busca R Teodorescu F Blaabjerg et al ldquoAn overview ofthe reliability prediction related aspects of high power IGBTsin wind power applicationsrdquoMicroelectronics Reliability vol 51no 9ndash11 pp 1903ndash1907 2011
[46] ABB ldquoApplication NotemdashApplying IGBTsrdquo 2014 httpwwwabbcom
[47] A Volke and M Hornkamp IGBT ModulesmdashTechnologiesDriver and Application Infineon Technologies AG MunichGermany 2012
[48] U Scheuermann ldquoReliability of advanced power modules forextended maximum junction temperaturesrdquo Bodorsquos Power Sys-tems pp 26ndash30 2014
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
4 International Journal of Photoenergy
Power losses Device temp
Electrical domain
Thermal domain
Junction Case Heat-sink Ambient
Pin Poutinvdc
(Ploss = Pin minus Pout)Tj Tc Th Ta
Zth(j-c)Zth(c-h) Zth(h-a)
Figure 5 Coupled relationship between power losses and the junction temperature of the power switching devices 119885th(119895-119888) junction to caseimpedance 119885th(119888-ℎ) case to heat-sink impedance and 119885th(ℎ-119886) heat-sink to ambient impedance
Tc
Tj
Ptot
Ta
Rth1 Rth2 Rth3 Rth4
C1 C2 C3 C4
Ci = 120591iRthiZth(j-c)
Figure 6 Foster model of the junction to case thermal impedance 119885th(119895-119888) shown in Figure 5
Table 2 System parameters for single-phase transformerless grid-connected PV systems
Parameter Symbol Value UnitGrid voltage V
119892RMS 230 VGrid frequency 119891
119892 50 Hz
LCL-filter1198711
36 mH119862119891 235 120583F
1198712
4 mHDamping resistor 119877
11988910 Ω
Switching frequency 119891119904
10 kHzParameters of PV strings (3 strings 15 panels for each string)
at 25∘C and 1 kWm2
Power at MPP 119875MPP 299 kWVoltage at MPP 119881MPP 405 VCurrent at MPP 119868MPP 738 A
shown in Table 2 In order to create the lookup tables forlong-termmission profiles several constant operating condi-tions (eg solar irradiance 08 kWm2 ambient temperature25∘C) have been simulated firstly where a perturb-and-observe maximum power point (MPP) tracking algorithmhas been used [33ndash35 38] Figure 7 exemplifies the simulationmodel for a full-bridge inverter system A proportional reso-nant current controller has been adopted to control the gridcurrent considering power quality requirements [2] Using
the lookup table model the yearly mission profile (Figure 3)has been resampled (5minssample) and translated intothe thermal loading of the corresponding power switchingdevices as it is presented in Figure 8
Although the transformerless PV inverters (both the H6and the HERIC) can maintain a higher efficiency as reportedin the literature in contrast to the FB-Bipolar inverter thethermal loading on those switching devices is unequal as itcan be seen in Figure 8 Specifically the maximum junctiontemperature of the extra devices in an H6 inverter is thehighest indicating high power losses since they are switchedat a high frequency However this is not the case for theHERIC inverter where only one of the extra switchingdevices is switched at the grid frequency during a half cycleTherefore the power losses are lower and thus the thermalloading as it is shown in Figure 8 From the above qualitativeanalysis it is implied that much attention has to be paid onthe extra switching devices in transformerless PV invertersParticularly for theH6 inverter power switching deviceswithlower conduction losses and higher rated maximum junctiontemperature are desirable while the total cost has to be takeninto consideration as well
When the thermal loading profile appearing in the powerswitching devices is available a quantitative prediction ofthe device lifetime under the mission profile is enabled by arain-flow counting algorithm [41 42]The rain-flow countingalgorithm is a quantitative representation of the thermalloading which extracts the temperature information in detailin terms of the mean junction temperature 119879
119895119898 temperature
International Journal of Photoenergy 5
STa
PV++
+++
+
minus
minus
A
CC
A
V VCPVC 11e minus 3
PV
iPV
PWM
1
2 345
Full-bridgeinverter
a
a
b
b
R1 R2L1 L2
Cf GridRd
s
ig
gControl system
Probe
Probe
Probe
Probe
Probe
Probe
Probe
Probe
ProbeVac
Iac
PV V I P
PV P V
AC grid
PV string
P versus V
s
+
minus
f(u)
f(u)
f(u)
f(u)
D1
D2 D4
D3
Heat sink
IGBT1
IGBT2
IGBT3
IGBT4
Scope
Thermal chain T tint
Figure 7 Simulation model of a single-phase full-bridge PV inverter system in PLECS
FB-bipolar
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
S1ndash4
S1ndash4
S1ndash4
1011 0312 0912Time of a year (monthyear)
1011 0312 0912Time of a year (monthyear)
1011 0312 0912Time of a year (monthyear)
H6
Extra devices S56
Extra devices S56
HERIC
(a)
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
S1ndash4
S1ndash4
S1ndash4
Extra devices S56
Extra devices S56
Time of a day (hoursmin)0000 1200 2400
Time of a day (hoursmin)0000 1200 2400
Time of a day (hoursmin)0000 1200 2400
(b)
Figure 8 Translated thermal loading (maximum junction temperature 119879119895max) of the power switching devices of the three different
transformerless grid-connected PV inverters under a yearly mission profile shown in Figure 3 (a) the yearly long-term thermal loadingand (b) details of the maximum junction temperature of the power switching devices in a cloudy day of the year
6 International Journal of Photoenergy
Table 3 Parameters of the lifetime model for power devices [48]
Parameter Value Unit Experimental condition119860 34368 times 1014 mdash120572 minus4923 mdash 64K le Δ119879
119895le 113 K
1205730
1942 mdash 019 le ar le 0421205731
minus9012 times 10minus3 mdash119862 1434 mdash 007 s le 119905
119900119899le 63 s
120574 minus1208 mdash119891119889
06204 mdash119864119886
006606 eV 325∘C le 119879119895119898
le 122∘C119896119861
86173324 times 10minus5 eVK
cycle amplitude 119879119895 cycle period 119905
119900119899 number of cycles n and
so forthThen the extracted temperature information can beused for the lifetime prediction according to a specific lifetimemodel For example a lifetime model of power switchingdevices is introduced in [48] and it can be expressed as
119873119891= 119860Δ119879
120572
119895(119886119903)1205731Δ119879119895+1205730 (
119862 + (119905119900119899)120574
119862 + 1) exp(
119864119886
119896119861119879119895119898
)119891119889
(1)
where119873119891is the number of cycles to fail119891
119889is the diode effect
119886119903 is the bond-wire aspect ratio 119896119861is the Boltzmann constant
119864119886is the activation energy and 119860 120572 120573
0 1205731 120574 and 119862 are
the lifetime model parameters as it is shown in Table 3 Thelifetime model also implies that the junction temperature hasa significant impact on the number of cycles to fail that is thereliability of the power switching devices
According to Minerrsquos rule [24 42 48] the life consump-tion LC the damage due to the thermal stress is the linearlyaccumulative damage from different thermal cycles The LCcan then be expressed as
119871119862 = sum
119894
119899119894
119873119891119894
(2)
in which 119899119894is the number of cycles at the stressΔ119879
119895119894extracted
by the rain-flow counting algorithm and 119873119891119894is the number
of cycles to fail based on (1) Subsequently the lifetime of thepower switching devices can be given as
119871119875=119905119872119875
119871119862(3)
with 119871119875being the predicted lifetime and 119905
119872119875being the
mission profile period (eg a year)Using the above reliability analysis procedure the lifetime
of the power switching devices in the transformerless PVinverters can then be estimated as long as a mission profileand a lifetimemodel of high confidence are available Figure 9summarizes the mission profile based analysis approachwhich can also be used in other power electronics convertersfor example wind turbine converters where the missionprofiles are available
Mission profile
Mission profiletranslation
Thermal loadinginterpretation
Lifetimeprediction
∘C
System models
Loading profilecounting
Lifetimemodels
Counting algorithms
Extracted thermal info
∙ Level crossing∙ Rain-flow∙ Simple range counting∙ middot middot middot
∙ middot middot middot
∙ Tjm-mean junction temp∙ ΔTj-temp cycle amplitude∙ ton -cycle period
Figure 9 Flowchart of the mission profile based reliability analysisapproach for transformerless PV inverters
4 Reliability Assessment
According to Figure 9 the lifetime of the power switchingdevices in the three transformerless PV inverters under theyearly mission profile shown in Figure 3 can be obtained andevaluated In order to benchmark the reliability quantita-tively the thermal loading profiles have to be interpreted firstaccording to (1) and Figure 9 A rain-flow counting algorithmhas been adopted and the results are presented in Figure 10It can be observed in Figure 10 that the additional devicesof the H6 inverter (ie S
5and S
6) have a larger number
of cycles compared to the other power switching devices ofthis topology (S
1sim4) This indicates that the extra devices to
realize an elimination of the leakage currents become themost critical components of the H6 inverter according to(2) and (3) As a consequence more reliable power devicesare preferable as the extra devices when designing an H6based transformerless PV system In the case of the HERICinverter based transformerless PV systems the extra deviceshave a smaller number of cycles compared to those of theH6 inverter Moreover the number of cycles of the otherpower switching devices of theHERC inverter is even smallerthan that of the FB-Bipolar inverter under the same missionprofile This means that the thermal stress on the powerswitching devices of the HERIC inverter is the lowest andthus the HERIC inverter can achieve the highest reliabilityif the same mission profile is applied to those invertercandidates while also maintaining a higher efficiency as itis reported in [12 14] The discussion is in agreement withthe analysis presented in Section 33 based on the translatedthermal loading profiles
It should be noted that the life consumption and thusthe lifetime of the power switching devices according to (2)and (3) can quantitatively be obtained on condition that thelifetime model of (1) and also the parameters given in Table 3are at a high confident level However those parameters are
International Journal of Photoenergy 7
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
(a)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15 minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
S56
S56
(b)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4S56
S56
(c)
Figure 10 Rain-flowing counting results (number of cycles distributions at the cycle amplitude Δ119879119895and the mean junction temperature 119879
119895119898)
of the thermal loading profiles shown in Figure 8 (a) FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
8 International Journal of Photoenergy
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
(a)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
S56
(b)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4S56
(c)
Figure 11 Normalized life consumption (lifetime comparison) of the three transformerless PV inverters under the same mission profile (a)FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
extracted under specific conditions (eg 007 s le 119905119900119899
le
63 s) for the power switching devices introduced in [48]Therefore quantitative prediction errors will be inevitableIn order to reduce the parameter dependency and also thereliability model dependency the life consumption given in(2) is normalized and substituting (1) yields
119871119862 =119871119862
119871119862119887
= (sum
119894
119899119894
(Δ119879119895119894)120572
(119886119903)1205731Δ119879119895119894 [119862 + (119905
119900119899119894)120574] 119890119864119886(119896119861119879119895119898119894))
sdot (sum
119897
119899119897
(Δ1198791015840
119895119897)120572
(119886119903)1205731Δ1198791015840
119895119897 [119862 + (1199051015840
119900119899119897)120574] 119890119864119886(1198961198611198791015840
119895119898119897)
)
minus1
(4)
where 119871119862 is the normalized life consumption and LCb is thebase LC for normalization For example LCb can be chosenas the life consumption of the power switching devices of theFB-Bipolar inverter under the samemission profileThen thepredicted lifetime can be expressed as
119871119901=
1
1198711198621198711015840
119901(5)
in which 1198711015840
119901is the predicted lifetime of the base system used
for normalizationFigure 11 shows the normalized life consumption of the
three transformerless PV inverters according to (4) and thecounting results enabled by a rain-flow algorithm The lifeconsumption of the power switching devices of the FB-Bipolar (ie S
1sim4) is selected as the base life consumption for
normalization in Figure 11 It can be seen in Figure 11 that theextra power switching devices of the H6 inverter consumemuch more life compared to the other devices and also thoseof the HERIC inverter It implies that the degradation of theadditional devices of the H6 inverter happens much fasterand then the entire H6 systemmay fail to operate earlier thanthe other two transformerless PV inverters This comparisonfurther confirms that the HERIC inverter would be the mostpromising solution in terms of reliability
In addition by comparing the rain-flow counting resultsshown in Figure 10 with the normalized life consumptionshown in Figure 11 one interesting conclusion can be drawnwhich is that although there are a few cycles of a largetemperature cycling amplitude (eg ten cycles of 55∘C to65∘C for the extra devices S
56of the H6 inverter) they do
contribute much more damage (eg 04 in Figure 11(b))when the lifetime model of (1) is adopted Large cyclingamplitude is mainly induced by the mission profile whichconfirms that the mission profile effect has to be taken intoaccount in a reliability-oriented design of power electronics
International Journal of Photoenergy 9
converters In a word the reliability assessment in this paperreveals that much attention has to be put on the thermaldesign of the critical components in an entire PV inverter inorder to reduce the cost of energy
5 Conclusions
In this paper a qualitative reliability assessment of threeselected single-phase transformerless PV inverters has beencarried out in accordance with a mission profile based reli-ability analysis approach A real-field yearly mission profilehas been applied to the selected transformerless candidatesfor the reliability assessment The comparison results haverevealed that although minimizing leakage currents as wellas maintaining a satisfactory efficiency has been targetedby those inverters the extra devices that are used fordisconnection of the PV panels or the PV inverters mightbe heated up during operation The high thermal loadingwill further induce failures of the power switching devicesbeing a big challenge to the entire system reliability As aconsequence many efforts should be devoted to a reliability-oriented design of the critical components in a PV inverterand thus a reduced cost of energy can be achieved
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F Blaabjerg K Ma and Y Yang ldquoPower electronicsmdashthe keytechnology for renewable energy systemsrdquo in Proceedings ofthe 9th International Conference on Ecological Vehicles andRenewable Energies (EVER rsquo14) pp 1ndash11 Monte-Carlo MonacoMarch 2014
[2] 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
[3] J M Carrasco L G Franquelo J T Bialasiewicz et al ldquoPower-electronic systems for the grid integration of renewable energysources a surveyrdquo IEEE Transactions on Industrial Electronicsvol 53 no 4 pp 1002ndash1016 2006
[4] J D vanWyk and F C Lee ldquoOn a future for power electronicsrdquoIEEE Journal of Emerging and Selected Topics in Power Electron-ics vol 1 no 2 pp 59ndash72 2013
[5] A Golnas ldquoPV system reliability an operatorrsquos perspectiverdquoIEEE Journal of Photovoltaics vol 3 no 1 pp 416ndash421 2013
[6] A Ristow M Begovic A Pregelj and A Rohatgi ldquoDevelop-ment of a methodology for improving photovoltaic inverterreliabilityrdquo IEEE Transactions on Industrial Electronics vol 55no 7 pp 2581ndash2592 2008
[7] E Romero-Cadaval G Spagnuolo L G Franquelo C ARamos-Paja T Suntio and W M Xiao ldquoGrid-connectedphotovoltaic generation plants components and operationrdquoIEEE Industrial ElectronicsMagazine vol 7 no 3 pp 6ndash20 2013
[8] REN21 ldquoRenewables 2014 global status reportrdquo Tech Rep 2014httpwwwren21net
[9] M Liserre T Sauter and J Y Hung ldquoFuture energy systemsintegrating renewable energy sources into the smart power
grid through industrial electronicsrdquo IEEE Industrial ElectronicsMagazine vol 4 no 1 pp 18ndash37 2010
[10] C-L Shen and S-H Yang ldquoMulti-input converter with MPPTfeature for wind-PV power generation systemrdquo InternationalJournal of Photoenergy vol 2013 Article ID 129254 13 pages2013
[11] F Blaabjerg and K Ma ldquoFuture on power electronics for windturbine systemsrdquo IEEE Journal of Emerging and Selected Topicsin Power Electronics vol 1 no 3 pp 139ndash152 2013
[12] R TeodorescuM Liserre and P RodriguezGrid Converters forPhotovoltaic and Wind Power Systems Wiley-IEEE Press 2011
[13] R Gonzalez J Lopez P Sanchis and L Marroyo ldquoTrans-formerless inverter for single-phase photovoltaic systemsrdquo IEEETransactions on Power Electronics vol 22 no 2 pp 693ndash6972007
[14] H Schmidt C Siedle and J Ketterer ldquoDCAC converter toconvert direct electric voltage into alternating voltage or intoalternating currentrdquo US Patent 7046534 2006
[15] T Kerekes M Liserre R Teodorescu C Klumpner and MSumner ldquoEvaluation of three-phase transformerless photo-voltaic inverter topologiesrdquo IEEE Transactions on Power Elec-tronics vol 24 no 9 pp 2202ndash2211 2009
[16] R Gonzalez E Gubıa J Lopez and L Marroyo ldquoTransformer-less single-phase multilevel-based photovoltaic inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 7 pp 2694ndash2702 2008
[17] Advanced Energy ldquoWhatrsquos ahead for PV inverter technologyrdquoGreentechsolar 2014 httpwwwgreentechmediacom
[18] I Patrao E Figueres F Gonzalez-Espın and G GarceraldquoTransformerless topologies for grid-connected single-phasephotovoltaic invertersrdquo Renewable and Sustainable EnergyReviews vol 15 no 7 pp 3423ndash3431 2011
[19] N Achilladelis E Koutroulis and F Blaabjerg ldquoOptimizedpulse width modulation for transformerless active-NPC invert-ersrdquo in Proceedings of the 16th European Conference on PowerElectronics and Applications (EPE rsquo14-ECCE Europe) pp 1ndash10Lappeenranta Finland August 2014
[20] S Saridakis E Koutroulis and F Blaabjerg ldquoOptimal design ofmodern transformerless PV inverter topologiesdrdquo IEEE Trans-actions on Energy Conversion vol 28 no 2 pp 394ndash404 2013
[21] Y Yang H Wang F Blaabjerg and K Ma ldquoMission profilebased multi-disciplinary analysis of power modules in single-phase transformerless photovoltaic invertersrdquo in Proceedingsof the 15th European Conference on Power Electronics andApplications (EPE rsquo13) pp 1ndash10 IEEE Lille France September2013
[22] S E de Leon-Aldaco H Calleja F Chan and H R Jimenez-Grajales ldquoEffect of the mission profile on the reliability of apower converter aimed at photovoltaic applicationsmdasha casestudyrdquo IEEE Transactions on Power Electronics vol 28 no 6pp 2998ndash3007 2013
[23] H Wang M Liserre and F Blaabjerg ldquoToward reliable powerelectronics challenges design tools and opportunitiesrdquo IEEEIndustrial Electronics Magazine vol 7 no 2 pp 17ndash26 2013
[24] H Huang and P A Mawby ldquoA lifetime estimation techniquefor voltage source invertersrdquo IEEE Transactions on PowerElectronics vol 28 no 8 pp 4113ndash4119 2013
[25] P McCluskey ldquoReliability of power electronics under thermalloadingrdquo in Proceedings of the 7th International Conference onIntegrated Power Electronics Systems (CIPS rsquo12) March 2012
10 International Journal of Photoenergy
[26] H Lu C Bailey and C Yin ldquoDesign for reliability of powerelectronics modulesrdquoMicroelectronics Reliability vol 49 no 9ndash11 pp 1250ndash1255 2009
[27] M Ciappa ldquoLifetime prediction on the base ofmission profilesrdquoMicroelectronics Reliability vol 45 no 9-11 pp 1293ndash1298 2005
[28] F Chan and H Calleja ldquoReliability estimation of three single-phase topologies in grid-connected PV systemsrdquo IEEE Trans-actions on Industrial Electronics vol 58 no 7 pp 2683ndash26892011
[29] K Ma M Liserre F Blaabjerg and T Kerekes ldquoThermalloading and lifetime estimation for power device consideringmission profiles in wind power converterrdquo IEEE Transactionson Power Electronics vol 30 no 2 pp 590ndash602 2015
[30] S Harb and R S Balog ldquoReliability of candidate pho-tovoltaic module-integrated-inverter (PV-MII) topologiesmdashausagemodel approachrdquo IEEE Transactions on Power Electronicsvol 28 no 6 pp 3019ndash3027 2013
[31] P Zhang YWangW Xiao andW Li ldquoReliability evaluation ofgrid-connected photovoltaic power systemsrdquo IEEETransactionson Sustainable Energy vol 3 no 3 pp 379ndash389 2012
[32] S E De Leon-Aldaco H Calleja and J Aguayo ldquoReliability andmission profiles of photovoltaic systems a FIDES approachrdquoIEEE Transactions on Power Electronics vol 30 no 5 pp 2578ndash2586 2015
[33] S B Kjaer J K Pedersen and F Blaabjerg ldquoA review of single-phase grid-connected inverters for photovoltaicmodulesrdquo IEEETransactions on Industry Applications vol 41 no 5 pp 1292ndash1306 2005
[34] H Li J PengW Liu Z Huang andK-C Lin ldquoA newton-basedextremumseekingMPPTmethod for photovoltaic systemswithstochastic perturbationsrdquo International Journal of Photoenergyvol 2014 Article ID 938526 13 pages 2014
[35] D Sera L Mathe T Kerekes S V Spataru and R TeodoresculdquoOn the perturb-and-observe and incremental conductancemppt methods for PV systemsrdquo IEEE Journal of Photovoltaicsvol 3 no 3 pp 1070ndash1078 2013
[36] M Abdulkadir A H M Yatim and S T Yusuf ldquoAn improvedPSO-based MPPT control strategy for photovoltaic systemsrdquoInternational Journal of Photoenergy vol 2014 Article ID818232 11 pages 2014
[37] Y Zhou and H Li ldquoAnalysis and suppression of leakage cur-rent in cascaded-multilevel-inverter-based PV systemsrdquo IEEETransactions on Power Electronics vol 29 no 10 pp 5265ndash52772014
[38] A Hajiah T Khatib K Sopian and M Sebzali ldquoPerformanceof grid-connected photovoltaic system in two sites in KuwaitrdquoInternational Journal of Photoenergy vol 2012 Article ID178175 7 pages 2012
[39] M Musallam C Yin C Bailey and M Johnson ldquoMissionprofile-based reliability design and real-time life consumptionestimation in power electronicsrdquo IEEE Transactions on PowerElectronics vol 30 no 5 pp 2601ndash2613 2015
[40] Y Yang HWang F Blaabjerg and T Kerekes ldquoA hybrid powercontrol concept for PV inverters with reduced thermal loadingrdquoIEEE Transactions on Power Electronics vol 29 no 12 pp 6271ndash6275 2014
[41] A T Bryant P A Mawby P R Palmer E Santi and J LHudgins ldquoExploration of power device reliability using com-pact device models and fast electrothermal simulationrdquo IEEETransactions on Industry Applications vol 44 no 3 pp 894ndash903 2008
[42] M Musallam and C M Johnson ldquoAn efficient implementationof the rainflow counting algorithm for life consumption estima-tionrdquo IEEE Transactions on Reliability vol 61 no 4 pp 978ndash986 2012
[43] Plexim Gmbh ldquoPLECSmdashthe simulation platform for powerelectronics systemsrdquo Workshop Documentation 1 Aalborg2014
[44] I F Kovacevic U Drofenik and J W Kolar ldquoNew physicalmodel for lifetime estimation of powermodulesrdquo in Proceedingsof the International Power Electronics Conference (IPEC rsquo10) pp2106ndash2114 Sapporo Japan June 2010
[45] C Busca R Teodorescu F Blaabjerg et al ldquoAn overview ofthe reliability prediction related aspects of high power IGBTsin wind power applicationsrdquoMicroelectronics Reliability vol 51no 9ndash11 pp 1903ndash1907 2011
[46] ABB ldquoApplication NotemdashApplying IGBTsrdquo 2014 httpwwwabbcom
[47] A Volke and M Hornkamp IGBT ModulesmdashTechnologiesDriver and Application Infineon Technologies AG MunichGermany 2012
[48] U Scheuermann ldquoReliability of advanced power modules forextended maximum junction temperaturesrdquo Bodorsquos Power Sys-tems pp 26ndash30 2014
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 5
STa
PV++
+++
+
minus
minus
A
CC
A
V VCPVC 11e minus 3
PV
iPV
PWM
1
2 345
Full-bridgeinverter
a
a
b
b
R1 R2L1 L2
Cf GridRd
s
ig
gControl system
Probe
Probe
Probe
Probe
Probe
Probe
Probe
Probe
ProbeVac
Iac
PV V I P
PV P V
AC grid
PV string
P versus V
s
+
minus
f(u)
f(u)
f(u)
f(u)
D1
D2 D4
D3
Heat sink
IGBT1
IGBT2
IGBT3
IGBT4
Scope
Thermal chain T tint
Figure 7 Simulation model of a single-phase full-bridge PV inverter system in PLECS
FB-bipolar
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
S1ndash4
S1ndash4
S1ndash4
1011 0312 0912Time of a year (monthyear)
1011 0312 0912Time of a year (monthyear)
1011 0312 0912Time of a year (monthyear)
H6
Extra devices S56
Extra devices S56
HERIC
(a)
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
Max
imum
junc
tion
tem
pTjm
ax(∘
C)
80
60
40
20
0
minus20
S1ndash4
S1ndash4
S1ndash4
Extra devices S56
Extra devices S56
Time of a day (hoursmin)0000 1200 2400
Time of a day (hoursmin)0000 1200 2400
Time of a day (hoursmin)0000 1200 2400
(b)
Figure 8 Translated thermal loading (maximum junction temperature 119879119895max) of the power switching devices of the three different
transformerless grid-connected PV inverters under a yearly mission profile shown in Figure 3 (a) the yearly long-term thermal loadingand (b) details of the maximum junction temperature of the power switching devices in a cloudy day of the year
6 International Journal of Photoenergy
Table 3 Parameters of the lifetime model for power devices [48]
Parameter Value Unit Experimental condition119860 34368 times 1014 mdash120572 minus4923 mdash 64K le Δ119879
119895le 113 K
1205730
1942 mdash 019 le ar le 0421205731
minus9012 times 10minus3 mdash119862 1434 mdash 007 s le 119905
119900119899le 63 s
120574 minus1208 mdash119891119889
06204 mdash119864119886
006606 eV 325∘C le 119879119895119898
le 122∘C119896119861
86173324 times 10minus5 eVK
cycle amplitude 119879119895 cycle period 119905
119900119899 number of cycles n and
so forthThen the extracted temperature information can beused for the lifetime prediction according to a specific lifetimemodel For example a lifetime model of power switchingdevices is introduced in [48] and it can be expressed as
119873119891= 119860Δ119879
120572
119895(119886119903)1205731Δ119879119895+1205730 (
119862 + (119905119900119899)120574
119862 + 1) exp(
119864119886
119896119861119879119895119898
)119891119889
(1)
where119873119891is the number of cycles to fail119891
119889is the diode effect
119886119903 is the bond-wire aspect ratio 119896119861is the Boltzmann constant
119864119886is the activation energy and 119860 120572 120573
0 1205731 120574 and 119862 are
the lifetime model parameters as it is shown in Table 3 Thelifetime model also implies that the junction temperature hasa significant impact on the number of cycles to fail that is thereliability of the power switching devices
According to Minerrsquos rule [24 42 48] the life consump-tion LC the damage due to the thermal stress is the linearlyaccumulative damage from different thermal cycles The LCcan then be expressed as
119871119862 = sum
119894
119899119894
119873119891119894
(2)
in which 119899119894is the number of cycles at the stressΔ119879
119895119894extracted
by the rain-flow counting algorithm and 119873119891119894is the number
of cycles to fail based on (1) Subsequently the lifetime of thepower switching devices can be given as
119871119875=119905119872119875
119871119862(3)
with 119871119875being the predicted lifetime and 119905
119872119875being the
mission profile period (eg a year)Using the above reliability analysis procedure the lifetime
of the power switching devices in the transformerless PVinverters can then be estimated as long as a mission profileand a lifetimemodel of high confidence are available Figure 9summarizes the mission profile based analysis approachwhich can also be used in other power electronics convertersfor example wind turbine converters where the missionprofiles are available
Mission profile
Mission profiletranslation
Thermal loadinginterpretation
Lifetimeprediction
∘C
System models
Loading profilecounting
Lifetimemodels
Counting algorithms
Extracted thermal info
∙ Level crossing∙ Rain-flow∙ Simple range counting∙ middot middot middot
∙ middot middot middot
∙ Tjm-mean junction temp∙ ΔTj-temp cycle amplitude∙ ton -cycle period
Figure 9 Flowchart of the mission profile based reliability analysisapproach for transformerless PV inverters
4 Reliability Assessment
According to Figure 9 the lifetime of the power switchingdevices in the three transformerless PV inverters under theyearly mission profile shown in Figure 3 can be obtained andevaluated In order to benchmark the reliability quantita-tively the thermal loading profiles have to be interpreted firstaccording to (1) and Figure 9 A rain-flow counting algorithmhas been adopted and the results are presented in Figure 10It can be observed in Figure 10 that the additional devicesof the H6 inverter (ie S
5and S
6) have a larger number
of cycles compared to the other power switching devices ofthis topology (S
1sim4) This indicates that the extra devices to
realize an elimination of the leakage currents become themost critical components of the H6 inverter according to(2) and (3) As a consequence more reliable power devicesare preferable as the extra devices when designing an H6based transformerless PV system In the case of the HERICinverter based transformerless PV systems the extra deviceshave a smaller number of cycles compared to those of theH6 inverter Moreover the number of cycles of the otherpower switching devices of theHERC inverter is even smallerthan that of the FB-Bipolar inverter under the same missionprofile This means that the thermal stress on the powerswitching devices of the HERIC inverter is the lowest andthus the HERIC inverter can achieve the highest reliabilityif the same mission profile is applied to those invertercandidates while also maintaining a higher efficiency as itis reported in [12 14] The discussion is in agreement withthe analysis presented in Section 33 based on the translatedthermal loading profiles
It should be noted that the life consumption and thusthe lifetime of the power switching devices according to (2)and (3) can quantitatively be obtained on condition that thelifetime model of (1) and also the parameters given in Table 3are at a high confident level However those parameters are
International Journal of Photoenergy 7
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
(a)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15 minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
S56
S56
(b)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4S56
S56
(c)
Figure 10 Rain-flowing counting results (number of cycles distributions at the cycle amplitude Δ119879119895and the mean junction temperature 119879
119895119898)
of the thermal loading profiles shown in Figure 8 (a) FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
8 International Journal of Photoenergy
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
(a)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
S56
(b)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4S56
(c)
Figure 11 Normalized life consumption (lifetime comparison) of the three transformerless PV inverters under the same mission profile (a)FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
extracted under specific conditions (eg 007 s le 119905119900119899
le
63 s) for the power switching devices introduced in [48]Therefore quantitative prediction errors will be inevitableIn order to reduce the parameter dependency and also thereliability model dependency the life consumption given in(2) is normalized and substituting (1) yields
119871119862 =119871119862
119871119862119887
= (sum
119894
119899119894
(Δ119879119895119894)120572
(119886119903)1205731Δ119879119895119894 [119862 + (119905
119900119899119894)120574] 119890119864119886(119896119861119879119895119898119894))
sdot (sum
119897
119899119897
(Δ1198791015840
119895119897)120572
(119886119903)1205731Δ1198791015840
119895119897 [119862 + (1199051015840
119900119899119897)120574] 119890119864119886(1198961198611198791015840
119895119898119897)
)
minus1
(4)
where 119871119862 is the normalized life consumption and LCb is thebase LC for normalization For example LCb can be chosenas the life consumption of the power switching devices of theFB-Bipolar inverter under the samemission profileThen thepredicted lifetime can be expressed as
119871119901=
1
1198711198621198711015840
119901(5)
in which 1198711015840
119901is the predicted lifetime of the base system used
for normalizationFigure 11 shows the normalized life consumption of the
three transformerless PV inverters according to (4) and thecounting results enabled by a rain-flow algorithm The lifeconsumption of the power switching devices of the FB-Bipolar (ie S
1sim4) is selected as the base life consumption for
normalization in Figure 11 It can be seen in Figure 11 that theextra power switching devices of the H6 inverter consumemuch more life compared to the other devices and also thoseof the HERIC inverter It implies that the degradation of theadditional devices of the H6 inverter happens much fasterand then the entire H6 systemmay fail to operate earlier thanthe other two transformerless PV inverters This comparisonfurther confirms that the HERIC inverter would be the mostpromising solution in terms of reliability
In addition by comparing the rain-flow counting resultsshown in Figure 10 with the normalized life consumptionshown in Figure 11 one interesting conclusion can be drawnwhich is that although there are a few cycles of a largetemperature cycling amplitude (eg ten cycles of 55∘C to65∘C for the extra devices S
56of the H6 inverter) they do
contribute much more damage (eg 04 in Figure 11(b))when the lifetime model of (1) is adopted Large cyclingamplitude is mainly induced by the mission profile whichconfirms that the mission profile effect has to be taken intoaccount in a reliability-oriented design of power electronics
International Journal of Photoenergy 9
converters In a word the reliability assessment in this paperreveals that much attention has to be put on the thermaldesign of the critical components in an entire PV inverter inorder to reduce the cost of energy
5 Conclusions
In this paper a qualitative reliability assessment of threeselected single-phase transformerless PV inverters has beencarried out in accordance with a mission profile based reli-ability analysis approach A real-field yearly mission profilehas been applied to the selected transformerless candidatesfor the reliability assessment The comparison results haverevealed that although minimizing leakage currents as wellas maintaining a satisfactory efficiency has been targetedby those inverters the extra devices that are used fordisconnection of the PV panels or the PV inverters mightbe heated up during operation The high thermal loadingwill further induce failures of the power switching devicesbeing a big challenge to the entire system reliability As aconsequence many efforts should be devoted to a reliability-oriented design of the critical components in a PV inverterand thus a reduced cost of energy can be achieved
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F Blaabjerg K Ma and Y Yang ldquoPower electronicsmdashthe keytechnology for renewable energy systemsrdquo in Proceedings ofthe 9th International Conference on Ecological Vehicles andRenewable Energies (EVER rsquo14) pp 1ndash11 Monte-Carlo MonacoMarch 2014
[2] 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
[3] J M Carrasco L G Franquelo J T Bialasiewicz et al ldquoPower-electronic systems for the grid integration of renewable energysources a surveyrdquo IEEE Transactions on Industrial Electronicsvol 53 no 4 pp 1002ndash1016 2006
[4] J D vanWyk and F C Lee ldquoOn a future for power electronicsrdquoIEEE Journal of Emerging and Selected Topics in Power Electron-ics vol 1 no 2 pp 59ndash72 2013
[5] A Golnas ldquoPV system reliability an operatorrsquos perspectiverdquoIEEE Journal of Photovoltaics vol 3 no 1 pp 416ndash421 2013
[6] A Ristow M Begovic A Pregelj and A Rohatgi ldquoDevelop-ment of a methodology for improving photovoltaic inverterreliabilityrdquo IEEE Transactions on Industrial Electronics vol 55no 7 pp 2581ndash2592 2008
[7] E Romero-Cadaval G Spagnuolo L G Franquelo C ARamos-Paja T Suntio and W M Xiao ldquoGrid-connectedphotovoltaic generation plants components and operationrdquoIEEE Industrial ElectronicsMagazine vol 7 no 3 pp 6ndash20 2013
[8] REN21 ldquoRenewables 2014 global status reportrdquo Tech Rep 2014httpwwwren21net
[9] M Liserre T Sauter and J Y Hung ldquoFuture energy systemsintegrating renewable energy sources into the smart power
grid through industrial electronicsrdquo IEEE Industrial ElectronicsMagazine vol 4 no 1 pp 18ndash37 2010
[10] C-L Shen and S-H Yang ldquoMulti-input converter with MPPTfeature for wind-PV power generation systemrdquo InternationalJournal of Photoenergy vol 2013 Article ID 129254 13 pages2013
[11] F Blaabjerg and K Ma ldquoFuture on power electronics for windturbine systemsrdquo IEEE Journal of Emerging and Selected Topicsin Power Electronics vol 1 no 3 pp 139ndash152 2013
[12] R TeodorescuM Liserre and P RodriguezGrid Converters forPhotovoltaic and Wind Power Systems Wiley-IEEE Press 2011
[13] R Gonzalez J Lopez P Sanchis and L Marroyo ldquoTrans-formerless inverter for single-phase photovoltaic systemsrdquo IEEETransactions on Power Electronics vol 22 no 2 pp 693ndash6972007
[14] H Schmidt C Siedle and J Ketterer ldquoDCAC converter toconvert direct electric voltage into alternating voltage or intoalternating currentrdquo US Patent 7046534 2006
[15] T Kerekes M Liserre R Teodorescu C Klumpner and MSumner ldquoEvaluation of three-phase transformerless photo-voltaic inverter topologiesrdquo IEEE Transactions on Power Elec-tronics vol 24 no 9 pp 2202ndash2211 2009
[16] R Gonzalez E Gubıa J Lopez and L Marroyo ldquoTransformer-less single-phase multilevel-based photovoltaic inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 7 pp 2694ndash2702 2008
[17] Advanced Energy ldquoWhatrsquos ahead for PV inverter technologyrdquoGreentechsolar 2014 httpwwwgreentechmediacom
[18] I Patrao E Figueres F Gonzalez-Espın and G GarceraldquoTransformerless topologies for grid-connected single-phasephotovoltaic invertersrdquo Renewable and Sustainable EnergyReviews vol 15 no 7 pp 3423ndash3431 2011
[19] N Achilladelis E Koutroulis and F Blaabjerg ldquoOptimizedpulse width modulation for transformerless active-NPC invert-ersrdquo in Proceedings of the 16th European Conference on PowerElectronics and Applications (EPE rsquo14-ECCE Europe) pp 1ndash10Lappeenranta Finland August 2014
[20] S Saridakis E Koutroulis and F Blaabjerg ldquoOptimal design ofmodern transformerless PV inverter topologiesdrdquo IEEE Trans-actions on Energy Conversion vol 28 no 2 pp 394ndash404 2013
[21] Y Yang H Wang F Blaabjerg and K Ma ldquoMission profilebased multi-disciplinary analysis of power modules in single-phase transformerless photovoltaic invertersrdquo in Proceedingsof the 15th European Conference on Power Electronics andApplications (EPE rsquo13) pp 1ndash10 IEEE Lille France September2013
[22] S E de Leon-Aldaco H Calleja F Chan and H R Jimenez-Grajales ldquoEffect of the mission profile on the reliability of apower converter aimed at photovoltaic applicationsmdasha casestudyrdquo IEEE Transactions on Power Electronics vol 28 no 6pp 2998ndash3007 2013
[23] H Wang M Liserre and F Blaabjerg ldquoToward reliable powerelectronics challenges design tools and opportunitiesrdquo IEEEIndustrial Electronics Magazine vol 7 no 2 pp 17ndash26 2013
[24] H Huang and P A Mawby ldquoA lifetime estimation techniquefor voltage source invertersrdquo IEEE Transactions on PowerElectronics vol 28 no 8 pp 4113ndash4119 2013
[25] P McCluskey ldquoReliability of power electronics under thermalloadingrdquo in Proceedings of the 7th International Conference onIntegrated Power Electronics Systems (CIPS rsquo12) March 2012
10 International Journal of Photoenergy
[26] H Lu C Bailey and C Yin ldquoDesign for reliability of powerelectronics modulesrdquoMicroelectronics Reliability vol 49 no 9ndash11 pp 1250ndash1255 2009
[27] M Ciappa ldquoLifetime prediction on the base ofmission profilesrdquoMicroelectronics Reliability vol 45 no 9-11 pp 1293ndash1298 2005
[28] F Chan and H Calleja ldquoReliability estimation of three single-phase topologies in grid-connected PV systemsrdquo IEEE Trans-actions on Industrial Electronics vol 58 no 7 pp 2683ndash26892011
[29] K Ma M Liserre F Blaabjerg and T Kerekes ldquoThermalloading and lifetime estimation for power device consideringmission profiles in wind power converterrdquo IEEE Transactionson Power Electronics vol 30 no 2 pp 590ndash602 2015
[30] S Harb and R S Balog ldquoReliability of candidate pho-tovoltaic module-integrated-inverter (PV-MII) topologiesmdashausagemodel approachrdquo IEEE Transactions on Power Electronicsvol 28 no 6 pp 3019ndash3027 2013
[31] P Zhang YWangW Xiao andW Li ldquoReliability evaluation ofgrid-connected photovoltaic power systemsrdquo IEEETransactionson Sustainable Energy vol 3 no 3 pp 379ndash389 2012
[32] S E De Leon-Aldaco H Calleja and J Aguayo ldquoReliability andmission profiles of photovoltaic systems a FIDES approachrdquoIEEE Transactions on Power Electronics vol 30 no 5 pp 2578ndash2586 2015
[33] S B Kjaer J K Pedersen and F Blaabjerg ldquoA review of single-phase grid-connected inverters for photovoltaicmodulesrdquo IEEETransactions on Industry Applications vol 41 no 5 pp 1292ndash1306 2005
[34] H Li J PengW Liu Z Huang andK-C Lin ldquoA newton-basedextremumseekingMPPTmethod for photovoltaic systemswithstochastic perturbationsrdquo International Journal of Photoenergyvol 2014 Article ID 938526 13 pages 2014
[35] D Sera L Mathe T Kerekes S V Spataru and R TeodoresculdquoOn the perturb-and-observe and incremental conductancemppt methods for PV systemsrdquo IEEE Journal of Photovoltaicsvol 3 no 3 pp 1070ndash1078 2013
[36] M Abdulkadir A H M Yatim and S T Yusuf ldquoAn improvedPSO-based MPPT control strategy for photovoltaic systemsrdquoInternational Journal of Photoenergy vol 2014 Article ID818232 11 pages 2014
[37] Y Zhou and H Li ldquoAnalysis and suppression of leakage cur-rent in cascaded-multilevel-inverter-based PV systemsrdquo IEEETransactions on Power Electronics vol 29 no 10 pp 5265ndash52772014
[38] A Hajiah T Khatib K Sopian and M Sebzali ldquoPerformanceof grid-connected photovoltaic system in two sites in KuwaitrdquoInternational Journal of Photoenergy vol 2012 Article ID178175 7 pages 2012
[39] M Musallam C Yin C Bailey and M Johnson ldquoMissionprofile-based reliability design and real-time life consumptionestimation in power electronicsrdquo IEEE Transactions on PowerElectronics vol 30 no 5 pp 2601ndash2613 2015
[40] Y Yang HWang F Blaabjerg and T Kerekes ldquoA hybrid powercontrol concept for PV inverters with reduced thermal loadingrdquoIEEE Transactions on Power Electronics vol 29 no 12 pp 6271ndash6275 2014
[41] A T Bryant P A Mawby P R Palmer E Santi and J LHudgins ldquoExploration of power device reliability using com-pact device models and fast electrothermal simulationrdquo IEEETransactions on Industry Applications vol 44 no 3 pp 894ndash903 2008
[42] M Musallam and C M Johnson ldquoAn efficient implementationof the rainflow counting algorithm for life consumption estima-tionrdquo IEEE Transactions on Reliability vol 61 no 4 pp 978ndash986 2012
[43] Plexim Gmbh ldquoPLECSmdashthe simulation platform for powerelectronics systemsrdquo Workshop Documentation 1 Aalborg2014
[44] I F Kovacevic U Drofenik and J W Kolar ldquoNew physicalmodel for lifetime estimation of powermodulesrdquo in Proceedingsof the International Power Electronics Conference (IPEC rsquo10) pp2106ndash2114 Sapporo Japan June 2010
[45] C Busca R Teodorescu F Blaabjerg et al ldquoAn overview ofthe reliability prediction related aspects of high power IGBTsin wind power applicationsrdquoMicroelectronics Reliability vol 51no 9ndash11 pp 1903ndash1907 2011
[46] ABB ldquoApplication NotemdashApplying IGBTsrdquo 2014 httpwwwabbcom
[47] A Volke and M Hornkamp IGBT ModulesmdashTechnologiesDriver and Application Infineon Technologies AG MunichGermany 2012
[48] U Scheuermann ldquoReliability of advanced power modules forextended maximum junction temperaturesrdquo Bodorsquos Power Sys-tems pp 26ndash30 2014
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
6 International Journal of Photoenergy
Table 3 Parameters of the lifetime model for power devices [48]
Parameter Value Unit Experimental condition119860 34368 times 1014 mdash120572 minus4923 mdash 64K le Δ119879
119895le 113 K
1205730
1942 mdash 019 le ar le 0421205731
minus9012 times 10minus3 mdash119862 1434 mdash 007 s le 119905
119900119899le 63 s
120574 minus1208 mdash119891119889
06204 mdash119864119886
006606 eV 325∘C le 119879119895119898
le 122∘C119896119861
86173324 times 10minus5 eVK
cycle amplitude 119879119895 cycle period 119905
119900119899 number of cycles n and
so forthThen the extracted temperature information can beused for the lifetime prediction according to a specific lifetimemodel For example a lifetime model of power switchingdevices is introduced in [48] and it can be expressed as
119873119891= 119860Δ119879
120572
119895(119886119903)1205731Δ119879119895+1205730 (
119862 + (119905119900119899)120574
119862 + 1) exp(
119864119886
119896119861119879119895119898
)119891119889
(1)
where119873119891is the number of cycles to fail119891
119889is the diode effect
119886119903 is the bond-wire aspect ratio 119896119861is the Boltzmann constant
119864119886is the activation energy and 119860 120572 120573
0 1205731 120574 and 119862 are
the lifetime model parameters as it is shown in Table 3 Thelifetime model also implies that the junction temperature hasa significant impact on the number of cycles to fail that is thereliability of the power switching devices
According to Minerrsquos rule [24 42 48] the life consump-tion LC the damage due to the thermal stress is the linearlyaccumulative damage from different thermal cycles The LCcan then be expressed as
119871119862 = sum
119894
119899119894
119873119891119894
(2)
in which 119899119894is the number of cycles at the stressΔ119879
119895119894extracted
by the rain-flow counting algorithm and 119873119891119894is the number
of cycles to fail based on (1) Subsequently the lifetime of thepower switching devices can be given as
119871119875=119905119872119875
119871119862(3)
with 119871119875being the predicted lifetime and 119905
119872119875being the
mission profile period (eg a year)Using the above reliability analysis procedure the lifetime
of the power switching devices in the transformerless PVinverters can then be estimated as long as a mission profileand a lifetimemodel of high confidence are available Figure 9summarizes the mission profile based analysis approachwhich can also be used in other power electronics convertersfor example wind turbine converters where the missionprofiles are available
Mission profile
Mission profiletranslation
Thermal loadinginterpretation
Lifetimeprediction
∘C
System models
Loading profilecounting
Lifetimemodels
Counting algorithms
Extracted thermal info
∙ Level crossing∙ Rain-flow∙ Simple range counting∙ middot middot middot
∙ middot middot middot
∙ Tjm-mean junction temp∙ ΔTj-temp cycle amplitude∙ ton -cycle period
Figure 9 Flowchart of the mission profile based reliability analysisapproach for transformerless PV inverters
4 Reliability Assessment
According to Figure 9 the lifetime of the power switchingdevices in the three transformerless PV inverters under theyearly mission profile shown in Figure 3 can be obtained andevaluated In order to benchmark the reliability quantita-tively the thermal loading profiles have to be interpreted firstaccording to (1) and Figure 9 A rain-flow counting algorithmhas been adopted and the results are presented in Figure 10It can be observed in Figure 10 that the additional devicesof the H6 inverter (ie S
5and S
6) have a larger number
of cycles compared to the other power switching devices ofthis topology (S
1sim4) This indicates that the extra devices to
realize an elimination of the leakage currents become themost critical components of the H6 inverter according to(2) and (3) As a consequence more reliable power devicesare preferable as the extra devices when designing an H6based transformerless PV system In the case of the HERICinverter based transformerless PV systems the extra deviceshave a smaller number of cycles compared to those of theH6 inverter Moreover the number of cycles of the otherpower switching devices of theHERC inverter is even smallerthan that of the FB-Bipolar inverter under the same missionprofile This means that the thermal stress on the powerswitching devices of the HERIC inverter is the lowest andthus the HERIC inverter can achieve the highest reliabilityif the same mission profile is applied to those invertercandidates while also maintaining a higher efficiency as itis reported in [12 14] The discussion is in agreement withthe analysis presented in Section 33 based on the translatedthermal loading profiles
It should be noted that the life consumption and thusthe lifetime of the power switching devices according to (2)and (3) can quantitatively be obtained on condition that thelifetime model of (1) and also the parameters given in Table 3are at a high confident level However those parameters are
International Journal of Photoenergy 7
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
(a)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15 minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
S56
S56
(b)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4S56
S56
(c)
Figure 10 Rain-flowing counting results (number of cycles distributions at the cycle amplitude Δ119879119895and the mean junction temperature 119879
119895119898)
of the thermal loading profiles shown in Figure 8 (a) FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
8 International Journal of Photoenergy
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
(a)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
S56
(b)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4S56
(c)
Figure 11 Normalized life consumption (lifetime comparison) of the three transformerless PV inverters under the same mission profile (a)FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
extracted under specific conditions (eg 007 s le 119905119900119899
le
63 s) for the power switching devices introduced in [48]Therefore quantitative prediction errors will be inevitableIn order to reduce the parameter dependency and also thereliability model dependency the life consumption given in(2) is normalized and substituting (1) yields
119871119862 =119871119862
119871119862119887
= (sum
119894
119899119894
(Δ119879119895119894)120572
(119886119903)1205731Δ119879119895119894 [119862 + (119905
119900119899119894)120574] 119890119864119886(119896119861119879119895119898119894))
sdot (sum
119897
119899119897
(Δ1198791015840
119895119897)120572
(119886119903)1205731Δ1198791015840
119895119897 [119862 + (1199051015840
119900119899119897)120574] 119890119864119886(1198961198611198791015840
119895119898119897)
)
minus1
(4)
where 119871119862 is the normalized life consumption and LCb is thebase LC for normalization For example LCb can be chosenas the life consumption of the power switching devices of theFB-Bipolar inverter under the samemission profileThen thepredicted lifetime can be expressed as
119871119901=
1
1198711198621198711015840
119901(5)
in which 1198711015840
119901is the predicted lifetime of the base system used
for normalizationFigure 11 shows the normalized life consumption of the
three transformerless PV inverters according to (4) and thecounting results enabled by a rain-flow algorithm The lifeconsumption of the power switching devices of the FB-Bipolar (ie S
1sim4) is selected as the base life consumption for
normalization in Figure 11 It can be seen in Figure 11 that theextra power switching devices of the H6 inverter consumemuch more life compared to the other devices and also thoseof the HERIC inverter It implies that the degradation of theadditional devices of the H6 inverter happens much fasterand then the entire H6 systemmay fail to operate earlier thanthe other two transformerless PV inverters This comparisonfurther confirms that the HERIC inverter would be the mostpromising solution in terms of reliability
In addition by comparing the rain-flow counting resultsshown in Figure 10 with the normalized life consumptionshown in Figure 11 one interesting conclusion can be drawnwhich is that although there are a few cycles of a largetemperature cycling amplitude (eg ten cycles of 55∘C to65∘C for the extra devices S
56of the H6 inverter) they do
contribute much more damage (eg 04 in Figure 11(b))when the lifetime model of (1) is adopted Large cyclingamplitude is mainly induced by the mission profile whichconfirms that the mission profile effect has to be taken intoaccount in a reliability-oriented design of power electronics
International Journal of Photoenergy 9
converters In a word the reliability assessment in this paperreveals that much attention has to be put on the thermaldesign of the critical components in an entire PV inverter inorder to reduce the cost of energy
5 Conclusions
In this paper a qualitative reliability assessment of threeselected single-phase transformerless PV inverters has beencarried out in accordance with a mission profile based reli-ability analysis approach A real-field yearly mission profilehas been applied to the selected transformerless candidatesfor the reliability assessment The comparison results haverevealed that although minimizing leakage currents as wellas maintaining a satisfactory efficiency has been targetedby those inverters the extra devices that are used fordisconnection of the PV panels or the PV inverters mightbe heated up during operation The high thermal loadingwill further induce failures of the power switching devicesbeing a big challenge to the entire system reliability As aconsequence many efforts should be devoted to a reliability-oriented design of the critical components in a PV inverterand thus a reduced cost of energy can be achieved
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F Blaabjerg K Ma and Y Yang ldquoPower electronicsmdashthe keytechnology for renewable energy systemsrdquo in Proceedings ofthe 9th International Conference on Ecological Vehicles andRenewable Energies (EVER rsquo14) pp 1ndash11 Monte-Carlo MonacoMarch 2014
[2] 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
[3] J M Carrasco L G Franquelo J T Bialasiewicz et al ldquoPower-electronic systems for the grid integration of renewable energysources a surveyrdquo IEEE Transactions on Industrial Electronicsvol 53 no 4 pp 1002ndash1016 2006
[4] J D vanWyk and F C Lee ldquoOn a future for power electronicsrdquoIEEE Journal of Emerging and Selected Topics in Power Electron-ics vol 1 no 2 pp 59ndash72 2013
[5] A Golnas ldquoPV system reliability an operatorrsquos perspectiverdquoIEEE Journal of Photovoltaics vol 3 no 1 pp 416ndash421 2013
[6] A Ristow M Begovic A Pregelj and A Rohatgi ldquoDevelop-ment of a methodology for improving photovoltaic inverterreliabilityrdquo IEEE Transactions on Industrial Electronics vol 55no 7 pp 2581ndash2592 2008
[7] E Romero-Cadaval G Spagnuolo L G Franquelo C ARamos-Paja T Suntio and W M Xiao ldquoGrid-connectedphotovoltaic generation plants components and operationrdquoIEEE Industrial ElectronicsMagazine vol 7 no 3 pp 6ndash20 2013
[8] REN21 ldquoRenewables 2014 global status reportrdquo Tech Rep 2014httpwwwren21net
[9] M Liserre T Sauter and J Y Hung ldquoFuture energy systemsintegrating renewable energy sources into the smart power
grid through industrial electronicsrdquo IEEE Industrial ElectronicsMagazine vol 4 no 1 pp 18ndash37 2010
[10] C-L Shen and S-H Yang ldquoMulti-input converter with MPPTfeature for wind-PV power generation systemrdquo InternationalJournal of Photoenergy vol 2013 Article ID 129254 13 pages2013
[11] F Blaabjerg and K Ma ldquoFuture on power electronics for windturbine systemsrdquo IEEE Journal of Emerging and Selected Topicsin Power Electronics vol 1 no 3 pp 139ndash152 2013
[12] R TeodorescuM Liserre and P RodriguezGrid Converters forPhotovoltaic and Wind Power Systems Wiley-IEEE Press 2011
[13] R Gonzalez J Lopez P Sanchis and L Marroyo ldquoTrans-formerless inverter for single-phase photovoltaic systemsrdquo IEEETransactions on Power Electronics vol 22 no 2 pp 693ndash6972007
[14] H Schmidt C Siedle and J Ketterer ldquoDCAC converter toconvert direct electric voltage into alternating voltage or intoalternating currentrdquo US Patent 7046534 2006
[15] T Kerekes M Liserre R Teodorescu C Klumpner and MSumner ldquoEvaluation of three-phase transformerless photo-voltaic inverter topologiesrdquo IEEE Transactions on Power Elec-tronics vol 24 no 9 pp 2202ndash2211 2009
[16] R Gonzalez E Gubıa J Lopez and L Marroyo ldquoTransformer-less single-phase multilevel-based photovoltaic inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 7 pp 2694ndash2702 2008
[17] Advanced Energy ldquoWhatrsquos ahead for PV inverter technologyrdquoGreentechsolar 2014 httpwwwgreentechmediacom
[18] I Patrao E Figueres F Gonzalez-Espın and G GarceraldquoTransformerless topologies for grid-connected single-phasephotovoltaic invertersrdquo Renewable and Sustainable EnergyReviews vol 15 no 7 pp 3423ndash3431 2011
[19] N Achilladelis E Koutroulis and F Blaabjerg ldquoOptimizedpulse width modulation for transformerless active-NPC invert-ersrdquo in Proceedings of the 16th European Conference on PowerElectronics and Applications (EPE rsquo14-ECCE Europe) pp 1ndash10Lappeenranta Finland August 2014
[20] S Saridakis E Koutroulis and F Blaabjerg ldquoOptimal design ofmodern transformerless PV inverter topologiesdrdquo IEEE Trans-actions on Energy Conversion vol 28 no 2 pp 394ndash404 2013
[21] Y Yang H Wang F Blaabjerg and K Ma ldquoMission profilebased multi-disciplinary analysis of power modules in single-phase transformerless photovoltaic invertersrdquo in Proceedingsof the 15th European Conference on Power Electronics andApplications (EPE rsquo13) pp 1ndash10 IEEE Lille France September2013
[22] S E de Leon-Aldaco H Calleja F Chan and H R Jimenez-Grajales ldquoEffect of the mission profile on the reliability of apower converter aimed at photovoltaic applicationsmdasha casestudyrdquo IEEE Transactions on Power Electronics vol 28 no 6pp 2998ndash3007 2013
[23] H Wang M Liserre and F Blaabjerg ldquoToward reliable powerelectronics challenges design tools and opportunitiesrdquo IEEEIndustrial Electronics Magazine vol 7 no 2 pp 17ndash26 2013
[24] H Huang and P A Mawby ldquoA lifetime estimation techniquefor voltage source invertersrdquo IEEE Transactions on PowerElectronics vol 28 no 8 pp 4113ndash4119 2013
[25] P McCluskey ldquoReliability of power electronics under thermalloadingrdquo in Proceedings of the 7th International Conference onIntegrated Power Electronics Systems (CIPS rsquo12) March 2012
10 International Journal of Photoenergy
[26] H Lu C Bailey and C Yin ldquoDesign for reliability of powerelectronics modulesrdquoMicroelectronics Reliability vol 49 no 9ndash11 pp 1250ndash1255 2009
[27] M Ciappa ldquoLifetime prediction on the base ofmission profilesrdquoMicroelectronics Reliability vol 45 no 9-11 pp 1293ndash1298 2005
[28] F Chan and H Calleja ldquoReliability estimation of three single-phase topologies in grid-connected PV systemsrdquo IEEE Trans-actions on Industrial Electronics vol 58 no 7 pp 2683ndash26892011
[29] K Ma M Liserre F Blaabjerg and T Kerekes ldquoThermalloading and lifetime estimation for power device consideringmission profiles in wind power converterrdquo IEEE Transactionson Power Electronics vol 30 no 2 pp 590ndash602 2015
[30] S Harb and R S Balog ldquoReliability of candidate pho-tovoltaic module-integrated-inverter (PV-MII) topologiesmdashausagemodel approachrdquo IEEE Transactions on Power Electronicsvol 28 no 6 pp 3019ndash3027 2013
[31] P Zhang YWangW Xiao andW Li ldquoReliability evaluation ofgrid-connected photovoltaic power systemsrdquo IEEETransactionson Sustainable Energy vol 3 no 3 pp 379ndash389 2012
[32] S E De Leon-Aldaco H Calleja and J Aguayo ldquoReliability andmission profiles of photovoltaic systems a FIDES approachrdquoIEEE Transactions on Power Electronics vol 30 no 5 pp 2578ndash2586 2015
[33] S B Kjaer J K Pedersen and F Blaabjerg ldquoA review of single-phase grid-connected inverters for photovoltaicmodulesrdquo IEEETransactions on Industry Applications vol 41 no 5 pp 1292ndash1306 2005
[34] H Li J PengW Liu Z Huang andK-C Lin ldquoA newton-basedextremumseekingMPPTmethod for photovoltaic systemswithstochastic perturbationsrdquo International Journal of Photoenergyvol 2014 Article ID 938526 13 pages 2014
[35] D Sera L Mathe T Kerekes S V Spataru and R TeodoresculdquoOn the perturb-and-observe and incremental conductancemppt methods for PV systemsrdquo IEEE Journal of Photovoltaicsvol 3 no 3 pp 1070ndash1078 2013
[36] M Abdulkadir A H M Yatim and S T Yusuf ldquoAn improvedPSO-based MPPT control strategy for photovoltaic systemsrdquoInternational Journal of Photoenergy vol 2014 Article ID818232 11 pages 2014
[37] Y Zhou and H Li ldquoAnalysis and suppression of leakage cur-rent in cascaded-multilevel-inverter-based PV systemsrdquo IEEETransactions on Power Electronics vol 29 no 10 pp 5265ndash52772014
[38] A Hajiah T Khatib K Sopian and M Sebzali ldquoPerformanceof grid-connected photovoltaic system in two sites in KuwaitrdquoInternational Journal of Photoenergy vol 2012 Article ID178175 7 pages 2012
[39] M Musallam C Yin C Bailey and M Johnson ldquoMissionprofile-based reliability design and real-time life consumptionestimation in power electronicsrdquo IEEE Transactions on PowerElectronics vol 30 no 5 pp 2601ndash2613 2015
[40] Y Yang HWang F Blaabjerg and T Kerekes ldquoA hybrid powercontrol concept for PV inverters with reduced thermal loadingrdquoIEEE Transactions on Power Electronics vol 29 no 12 pp 6271ndash6275 2014
[41] A T Bryant P A Mawby P R Palmer E Santi and J LHudgins ldquoExploration of power device reliability using com-pact device models and fast electrothermal simulationrdquo IEEETransactions on Industry Applications vol 44 no 3 pp 894ndash903 2008
[42] M Musallam and C M Johnson ldquoAn efficient implementationof the rainflow counting algorithm for life consumption estima-tionrdquo IEEE Transactions on Reliability vol 61 no 4 pp 978ndash986 2012
[43] Plexim Gmbh ldquoPLECSmdashthe simulation platform for powerelectronics systemsrdquo Workshop Documentation 1 Aalborg2014
[44] I F Kovacevic U Drofenik and J W Kolar ldquoNew physicalmodel for lifetime estimation of powermodulesrdquo in Proceedingsof the International Power Electronics Conference (IPEC rsquo10) pp2106ndash2114 Sapporo Japan June 2010
[45] C Busca R Teodorescu F Blaabjerg et al ldquoAn overview ofthe reliability prediction related aspects of high power IGBTsin wind power applicationsrdquoMicroelectronics Reliability vol 51no 9ndash11 pp 1903ndash1907 2011
[46] ABB ldquoApplication NotemdashApplying IGBTsrdquo 2014 httpwwwabbcom
[47] A Volke and M Hornkamp IGBT ModulesmdashTechnologiesDriver and Application Infineon Technologies AG MunichGermany 2012
[48] U Scheuermann ldquoReliability of advanced power modules forextended maximum junction temperaturesrdquo Bodorsquos Power Sys-tems pp 26ndash30 2014
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 7
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
(a)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15 minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4
S56
S56
(b)
Num
ber o
f cyc
les
105
104
103
102
101
100
10minus1
ΔTj (∘C)0 5 15 25 35 45 55 65 75 85 95
Num
ber o
f cyc
les
104
103
102
101
100
10minus1
Tjm (∘C)minus25minus15minus5 5 15 25 35 45 55 65 75
S1ndash4
S1ndash4S56
S56
(c)
Figure 10 Rain-flowing counting results (number of cycles distributions at the cycle amplitude Δ119879119895and the mean junction temperature 119879
119895119898)
of the thermal loading profiles shown in Figure 8 (a) FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
8 International Journal of Photoenergy
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
(a)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
S56
(b)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4S56
(c)
Figure 11 Normalized life consumption (lifetime comparison) of the three transformerless PV inverters under the same mission profile (a)FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
extracted under specific conditions (eg 007 s le 119905119900119899
le
63 s) for the power switching devices introduced in [48]Therefore quantitative prediction errors will be inevitableIn order to reduce the parameter dependency and also thereliability model dependency the life consumption given in(2) is normalized and substituting (1) yields
119871119862 =119871119862
119871119862119887
= (sum
119894
119899119894
(Δ119879119895119894)120572
(119886119903)1205731Δ119879119895119894 [119862 + (119905
119900119899119894)120574] 119890119864119886(119896119861119879119895119898119894))
sdot (sum
119897
119899119897
(Δ1198791015840
119895119897)120572
(119886119903)1205731Δ1198791015840
119895119897 [119862 + (1199051015840
119900119899119897)120574] 119890119864119886(1198961198611198791015840
119895119898119897)
)
minus1
(4)
where 119871119862 is the normalized life consumption and LCb is thebase LC for normalization For example LCb can be chosenas the life consumption of the power switching devices of theFB-Bipolar inverter under the samemission profileThen thepredicted lifetime can be expressed as
119871119901=
1
1198711198621198711015840
119901(5)
in which 1198711015840
119901is the predicted lifetime of the base system used
for normalizationFigure 11 shows the normalized life consumption of the
three transformerless PV inverters according to (4) and thecounting results enabled by a rain-flow algorithm The lifeconsumption of the power switching devices of the FB-Bipolar (ie S
1sim4) is selected as the base life consumption for
normalization in Figure 11 It can be seen in Figure 11 that theextra power switching devices of the H6 inverter consumemuch more life compared to the other devices and also thoseof the HERIC inverter It implies that the degradation of theadditional devices of the H6 inverter happens much fasterand then the entire H6 systemmay fail to operate earlier thanthe other two transformerless PV inverters This comparisonfurther confirms that the HERIC inverter would be the mostpromising solution in terms of reliability
In addition by comparing the rain-flow counting resultsshown in Figure 10 with the normalized life consumptionshown in Figure 11 one interesting conclusion can be drawnwhich is that although there are a few cycles of a largetemperature cycling amplitude (eg ten cycles of 55∘C to65∘C for the extra devices S
56of the H6 inverter) they do
contribute much more damage (eg 04 in Figure 11(b))when the lifetime model of (1) is adopted Large cyclingamplitude is mainly induced by the mission profile whichconfirms that the mission profile effect has to be taken intoaccount in a reliability-oriented design of power electronics
International Journal of Photoenergy 9
converters In a word the reliability assessment in this paperreveals that much attention has to be put on the thermaldesign of the critical components in an entire PV inverter inorder to reduce the cost of energy
5 Conclusions
In this paper a qualitative reliability assessment of threeselected single-phase transformerless PV inverters has beencarried out in accordance with a mission profile based reli-ability analysis approach A real-field yearly mission profilehas been applied to the selected transformerless candidatesfor the reliability assessment The comparison results haverevealed that although minimizing leakage currents as wellas maintaining a satisfactory efficiency has been targetedby those inverters the extra devices that are used fordisconnection of the PV panels or the PV inverters mightbe heated up during operation The high thermal loadingwill further induce failures of the power switching devicesbeing a big challenge to the entire system reliability As aconsequence many efforts should be devoted to a reliability-oriented design of the critical components in a PV inverterand thus a reduced cost of energy can be achieved
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F Blaabjerg K Ma and Y Yang ldquoPower electronicsmdashthe keytechnology for renewable energy systemsrdquo in Proceedings ofthe 9th International Conference on Ecological Vehicles andRenewable Energies (EVER rsquo14) pp 1ndash11 Monte-Carlo MonacoMarch 2014
[2] 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
[3] J M Carrasco L G Franquelo J T Bialasiewicz et al ldquoPower-electronic systems for the grid integration of renewable energysources a surveyrdquo IEEE Transactions on Industrial Electronicsvol 53 no 4 pp 1002ndash1016 2006
[4] J D vanWyk and F C Lee ldquoOn a future for power electronicsrdquoIEEE Journal of Emerging and Selected Topics in Power Electron-ics vol 1 no 2 pp 59ndash72 2013
[5] A Golnas ldquoPV system reliability an operatorrsquos perspectiverdquoIEEE Journal of Photovoltaics vol 3 no 1 pp 416ndash421 2013
[6] A Ristow M Begovic A Pregelj and A Rohatgi ldquoDevelop-ment of a methodology for improving photovoltaic inverterreliabilityrdquo IEEE Transactions on Industrial Electronics vol 55no 7 pp 2581ndash2592 2008
[7] E Romero-Cadaval G Spagnuolo L G Franquelo C ARamos-Paja T Suntio and W M Xiao ldquoGrid-connectedphotovoltaic generation plants components and operationrdquoIEEE Industrial ElectronicsMagazine vol 7 no 3 pp 6ndash20 2013
[8] REN21 ldquoRenewables 2014 global status reportrdquo Tech Rep 2014httpwwwren21net
[9] M Liserre T Sauter and J Y Hung ldquoFuture energy systemsintegrating renewable energy sources into the smart power
grid through industrial electronicsrdquo IEEE Industrial ElectronicsMagazine vol 4 no 1 pp 18ndash37 2010
[10] C-L Shen and S-H Yang ldquoMulti-input converter with MPPTfeature for wind-PV power generation systemrdquo InternationalJournal of Photoenergy vol 2013 Article ID 129254 13 pages2013
[11] F Blaabjerg and K Ma ldquoFuture on power electronics for windturbine systemsrdquo IEEE Journal of Emerging and Selected Topicsin Power Electronics vol 1 no 3 pp 139ndash152 2013
[12] R TeodorescuM Liserre and P RodriguezGrid Converters forPhotovoltaic and Wind Power Systems Wiley-IEEE Press 2011
[13] R Gonzalez J Lopez P Sanchis and L Marroyo ldquoTrans-formerless inverter for single-phase photovoltaic systemsrdquo IEEETransactions on Power Electronics vol 22 no 2 pp 693ndash6972007
[14] H Schmidt C Siedle and J Ketterer ldquoDCAC converter toconvert direct electric voltage into alternating voltage or intoalternating currentrdquo US Patent 7046534 2006
[15] T Kerekes M Liserre R Teodorescu C Klumpner and MSumner ldquoEvaluation of three-phase transformerless photo-voltaic inverter topologiesrdquo IEEE Transactions on Power Elec-tronics vol 24 no 9 pp 2202ndash2211 2009
[16] R Gonzalez E Gubıa J Lopez and L Marroyo ldquoTransformer-less single-phase multilevel-based photovoltaic inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 7 pp 2694ndash2702 2008
[17] Advanced Energy ldquoWhatrsquos ahead for PV inverter technologyrdquoGreentechsolar 2014 httpwwwgreentechmediacom
[18] I Patrao E Figueres F Gonzalez-Espın and G GarceraldquoTransformerless topologies for grid-connected single-phasephotovoltaic invertersrdquo Renewable and Sustainable EnergyReviews vol 15 no 7 pp 3423ndash3431 2011
[19] N Achilladelis E Koutroulis and F Blaabjerg ldquoOptimizedpulse width modulation for transformerless active-NPC invert-ersrdquo in Proceedings of the 16th European Conference on PowerElectronics and Applications (EPE rsquo14-ECCE Europe) pp 1ndash10Lappeenranta Finland August 2014
[20] S Saridakis E Koutroulis and F Blaabjerg ldquoOptimal design ofmodern transformerless PV inverter topologiesdrdquo IEEE Trans-actions on Energy Conversion vol 28 no 2 pp 394ndash404 2013
[21] Y Yang H Wang F Blaabjerg and K Ma ldquoMission profilebased multi-disciplinary analysis of power modules in single-phase transformerless photovoltaic invertersrdquo in Proceedingsof the 15th European Conference on Power Electronics andApplications (EPE rsquo13) pp 1ndash10 IEEE Lille France September2013
[22] S E de Leon-Aldaco H Calleja F Chan and H R Jimenez-Grajales ldquoEffect of the mission profile on the reliability of apower converter aimed at photovoltaic applicationsmdasha casestudyrdquo IEEE Transactions on Power Electronics vol 28 no 6pp 2998ndash3007 2013
[23] H Wang M Liserre and F Blaabjerg ldquoToward reliable powerelectronics challenges design tools and opportunitiesrdquo IEEEIndustrial Electronics Magazine vol 7 no 2 pp 17ndash26 2013
[24] H Huang and P A Mawby ldquoA lifetime estimation techniquefor voltage source invertersrdquo IEEE Transactions on PowerElectronics vol 28 no 8 pp 4113ndash4119 2013
[25] P McCluskey ldquoReliability of power electronics under thermalloadingrdquo in Proceedings of the 7th International Conference onIntegrated Power Electronics Systems (CIPS rsquo12) March 2012
10 International Journal of Photoenergy
[26] H Lu C Bailey and C Yin ldquoDesign for reliability of powerelectronics modulesrdquoMicroelectronics Reliability vol 49 no 9ndash11 pp 1250ndash1255 2009
[27] M Ciappa ldquoLifetime prediction on the base ofmission profilesrdquoMicroelectronics Reliability vol 45 no 9-11 pp 1293ndash1298 2005
[28] F Chan and H Calleja ldquoReliability estimation of three single-phase topologies in grid-connected PV systemsrdquo IEEE Trans-actions on Industrial Electronics vol 58 no 7 pp 2683ndash26892011
[29] K Ma M Liserre F Blaabjerg and T Kerekes ldquoThermalloading and lifetime estimation for power device consideringmission profiles in wind power converterrdquo IEEE Transactionson Power Electronics vol 30 no 2 pp 590ndash602 2015
[30] S Harb and R S Balog ldquoReliability of candidate pho-tovoltaic module-integrated-inverter (PV-MII) topologiesmdashausagemodel approachrdquo IEEE Transactions on Power Electronicsvol 28 no 6 pp 3019ndash3027 2013
[31] P Zhang YWangW Xiao andW Li ldquoReliability evaluation ofgrid-connected photovoltaic power systemsrdquo IEEETransactionson Sustainable Energy vol 3 no 3 pp 379ndash389 2012
[32] S E De Leon-Aldaco H Calleja and J Aguayo ldquoReliability andmission profiles of photovoltaic systems a FIDES approachrdquoIEEE Transactions on Power Electronics vol 30 no 5 pp 2578ndash2586 2015
[33] S B Kjaer J K Pedersen and F Blaabjerg ldquoA review of single-phase grid-connected inverters for photovoltaicmodulesrdquo IEEETransactions on Industry Applications vol 41 no 5 pp 1292ndash1306 2005
[34] H Li J PengW Liu Z Huang andK-C Lin ldquoA newton-basedextremumseekingMPPTmethod for photovoltaic systemswithstochastic perturbationsrdquo International Journal of Photoenergyvol 2014 Article ID 938526 13 pages 2014
[35] D Sera L Mathe T Kerekes S V Spataru and R TeodoresculdquoOn the perturb-and-observe and incremental conductancemppt methods for PV systemsrdquo IEEE Journal of Photovoltaicsvol 3 no 3 pp 1070ndash1078 2013
[36] M Abdulkadir A H M Yatim and S T Yusuf ldquoAn improvedPSO-based MPPT control strategy for photovoltaic systemsrdquoInternational Journal of Photoenergy vol 2014 Article ID818232 11 pages 2014
[37] Y Zhou and H Li ldquoAnalysis and suppression of leakage cur-rent in cascaded-multilevel-inverter-based PV systemsrdquo IEEETransactions on Power Electronics vol 29 no 10 pp 5265ndash52772014
[38] A Hajiah T Khatib K Sopian and M Sebzali ldquoPerformanceof grid-connected photovoltaic system in two sites in KuwaitrdquoInternational Journal of Photoenergy vol 2012 Article ID178175 7 pages 2012
[39] M Musallam C Yin C Bailey and M Johnson ldquoMissionprofile-based reliability design and real-time life consumptionestimation in power electronicsrdquo IEEE Transactions on PowerElectronics vol 30 no 5 pp 2601ndash2613 2015
[40] Y Yang HWang F Blaabjerg and T Kerekes ldquoA hybrid powercontrol concept for PV inverters with reduced thermal loadingrdquoIEEE Transactions on Power Electronics vol 29 no 12 pp 6271ndash6275 2014
[41] A T Bryant P A Mawby P R Palmer E Santi and J LHudgins ldquoExploration of power device reliability using com-pact device models and fast electrothermal simulationrdquo IEEETransactions on Industry Applications vol 44 no 3 pp 894ndash903 2008
[42] M Musallam and C M Johnson ldquoAn efficient implementationof the rainflow counting algorithm for life consumption estima-tionrdquo IEEE Transactions on Reliability vol 61 no 4 pp 978ndash986 2012
[43] Plexim Gmbh ldquoPLECSmdashthe simulation platform for powerelectronics systemsrdquo Workshop Documentation 1 Aalborg2014
[44] I F Kovacevic U Drofenik and J W Kolar ldquoNew physicalmodel for lifetime estimation of powermodulesrdquo in Proceedingsof the International Power Electronics Conference (IPEC rsquo10) pp2106ndash2114 Sapporo Japan June 2010
[45] C Busca R Teodorescu F Blaabjerg et al ldquoAn overview ofthe reliability prediction related aspects of high power IGBTsin wind power applicationsrdquoMicroelectronics Reliability vol 51no 9ndash11 pp 1903ndash1907 2011
[46] ABB ldquoApplication NotemdashApplying IGBTsrdquo 2014 httpwwwabbcom
[47] A Volke and M Hornkamp IGBT ModulesmdashTechnologiesDriver and Application Infineon Technologies AG MunichGermany 2012
[48] U Scheuermann ldquoReliability of advanced power modules forextended maximum junction temperaturesrdquo Bodorsquos Power Sys-tems pp 26ndash30 2014
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
8 International Journal of Photoenergy
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
(a)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4
S56
(b)
ΔTj (∘C)0 5 15 35 55 75 95
Nor
mal
ized
LC
()
20
16
12
08
04
0
S1ndash4S56
(c)
Figure 11 Normalized life consumption (lifetime comparison) of the three transformerless PV inverters under the same mission profile (a)FB-Bipolar inverter (b) H6 inverter and (c) HERIC inverter
extracted under specific conditions (eg 007 s le 119905119900119899
le
63 s) for the power switching devices introduced in [48]Therefore quantitative prediction errors will be inevitableIn order to reduce the parameter dependency and also thereliability model dependency the life consumption given in(2) is normalized and substituting (1) yields
119871119862 =119871119862
119871119862119887
= (sum
119894
119899119894
(Δ119879119895119894)120572
(119886119903)1205731Δ119879119895119894 [119862 + (119905
119900119899119894)120574] 119890119864119886(119896119861119879119895119898119894))
sdot (sum
119897
119899119897
(Δ1198791015840
119895119897)120572
(119886119903)1205731Δ1198791015840
119895119897 [119862 + (1199051015840
119900119899119897)120574] 119890119864119886(1198961198611198791015840
119895119898119897)
)
minus1
(4)
where 119871119862 is the normalized life consumption and LCb is thebase LC for normalization For example LCb can be chosenas the life consumption of the power switching devices of theFB-Bipolar inverter under the samemission profileThen thepredicted lifetime can be expressed as
119871119901=
1
1198711198621198711015840
119901(5)
in which 1198711015840
119901is the predicted lifetime of the base system used
for normalizationFigure 11 shows the normalized life consumption of the
three transformerless PV inverters according to (4) and thecounting results enabled by a rain-flow algorithm The lifeconsumption of the power switching devices of the FB-Bipolar (ie S
1sim4) is selected as the base life consumption for
normalization in Figure 11 It can be seen in Figure 11 that theextra power switching devices of the H6 inverter consumemuch more life compared to the other devices and also thoseof the HERIC inverter It implies that the degradation of theadditional devices of the H6 inverter happens much fasterand then the entire H6 systemmay fail to operate earlier thanthe other two transformerless PV inverters This comparisonfurther confirms that the HERIC inverter would be the mostpromising solution in terms of reliability
In addition by comparing the rain-flow counting resultsshown in Figure 10 with the normalized life consumptionshown in Figure 11 one interesting conclusion can be drawnwhich is that although there are a few cycles of a largetemperature cycling amplitude (eg ten cycles of 55∘C to65∘C for the extra devices S
56of the H6 inverter) they do
contribute much more damage (eg 04 in Figure 11(b))when the lifetime model of (1) is adopted Large cyclingamplitude is mainly induced by the mission profile whichconfirms that the mission profile effect has to be taken intoaccount in a reliability-oriented design of power electronics
International Journal of Photoenergy 9
converters In a word the reliability assessment in this paperreveals that much attention has to be put on the thermaldesign of the critical components in an entire PV inverter inorder to reduce the cost of energy
5 Conclusions
In this paper a qualitative reliability assessment of threeselected single-phase transformerless PV inverters has beencarried out in accordance with a mission profile based reli-ability analysis approach A real-field yearly mission profilehas been applied to the selected transformerless candidatesfor the reliability assessment The comparison results haverevealed that although minimizing leakage currents as wellas maintaining a satisfactory efficiency has been targetedby those inverters the extra devices that are used fordisconnection of the PV panels or the PV inverters mightbe heated up during operation The high thermal loadingwill further induce failures of the power switching devicesbeing a big challenge to the entire system reliability As aconsequence many efforts should be devoted to a reliability-oriented design of the critical components in a PV inverterand thus a reduced cost of energy can be achieved
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F Blaabjerg K Ma and Y Yang ldquoPower electronicsmdashthe keytechnology for renewable energy systemsrdquo in Proceedings ofthe 9th International Conference on Ecological Vehicles andRenewable Energies (EVER rsquo14) pp 1ndash11 Monte-Carlo MonacoMarch 2014
[2] 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
[3] J M Carrasco L G Franquelo J T Bialasiewicz et al ldquoPower-electronic systems for the grid integration of renewable energysources a surveyrdquo IEEE Transactions on Industrial Electronicsvol 53 no 4 pp 1002ndash1016 2006
[4] J D vanWyk and F C Lee ldquoOn a future for power electronicsrdquoIEEE Journal of Emerging and Selected Topics in Power Electron-ics vol 1 no 2 pp 59ndash72 2013
[5] A Golnas ldquoPV system reliability an operatorrsquos perspectiverdquoIEEE Journal of Photovoltaics vol 3 no 1 pp 416ndash421 2013
[6] A Ristow M Begovic A Pregelj and A Rohatgi ldquoDevelop-ment of a methodology for improving photovoltaic inverterreliabilityrdquo IEEE Transactions on Industrial Electronics vol 55no 7 pp 2581ndash2592 2008
[7] E Romero-Cadaval G Spagnuolo L G Franquelo C ARamos-Paja T Suntio and W M Xiao ldquoGrid-connectedphotovoltaic generation plants components and operationrdquoIEEE Industrial ElectronicsMagazine vol 7 no 3 pp 6ndash20 2013
[8] REN21 ldquoRenewables 2014 global status reportrdquo Tech Rep 2014httpwwwren21net
[9] M Liserre T Sauter and J Y Hung ldquoFuture energy systemsintegrating renewable energy sources into the smart power
grid through industrial electronicsrdquo IEEE Industrial ElectronicsMagazine vol 4 no 1 pp 18ndash37 2010
[10] C-L Shen and S-H Yang ldquoMulti-input converter with MPPTfeature for wind-PV power generation systemrdquo InternationalJournal of Photoenergy vol 2013 Article ID 129254 13 pages2013
[11] F Blaabjerg and K Ma ldquoFuture on power electronics for windturbine systemsrdquo IEEE Journal of Emerging and Selected Topicsin Power Electronics vol 1 no 3 pp 139ndash152 2013
[12] R TeodorescuM Liserre and P RodriguezGrid Converters forPhotovoltaic and Wind Power Systems Wiley-IEEE Press 2011
[13] R Gonzalez J Lopez P Sanchis and L Marroyo ldquoTrans-formerless inverter for single-phase photovoltaic systemsrdquo IEEETransactions on Power Electronics vol 22 no 2 pp 693ndash6972007
[14] H Schmidt C Siedle and J Ketterer ldquoDCAC converter toconvert direct electric voltage into alternating voltage or intoalternating currentrdquo US Patent 7046534 2006
[15] T Kerekes M Liserre R Teodorescu C Klumpner and MSumner ldquoEvaluation of three-phase transformerless photo-voltaic inverter topologiesrdquo IEEE Transactions on Power Elec-tronics vol 24 no 9 pp 2202ndash2211 2009
[16] R Gonzalez E Gubıa J Lopez and L Marroyo ldquoTransformer-less single-phase multilevel-based photovoltaic inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 7 pp 2694ndash2702 2008
[17] Advanced Energy ldquoWhatrsquos ahead for PV inverter technologyrdquoGreentechsolar 2014 httpwwwgreentechmediacom
[18] I Patrao E Figueres F Gonzalez-Espın and G GarceraldquoTransformerless topologies for grid-connected single-phasephotovoltaic invertersrdquo Renewable and Sustainable EnergyReviews vol 15 no 7 pp 3423ndash3431 2011
[19] N Achilladelis E Koutroulis and F Blaabjerg ldquoOptimizedpulse width modulation for transformerless active-NPC invert-ersrdquo in Proceedings of the 16th European Conference on PowerElectronics and Applications (EPE rsquo14-ECCE Europe) pp 1ndash10Lappeenranta Finland August 2014
[20] S Saridakis E Koutroulis and F Blaabjerg ldquoOptimal design ofmodern transformerless PV inverter topologiesdrdquo IEEE Trans-actions on Energy Conversion vol 28 no 2 pp 394ndash404 2013
[21] Y Yang H Wang F Blaabjerg and K Ma ldquoMission profilebased multi-disciplinary analysis of power modules in single-phase transformerless photovoltaic invertersrdquo in Proceedingsof the 15th European Conference on Power Electronics andApplications (EPE rsquo13) pp 1ndash10 IEEE Lille France September2013
[22] S E de Leon-Aldaco H Calleja F Chan and H R Jimenez-Grajales ldquoEffect of the mission profile on the reliability of apower converter aimed at photovoltaic applicationsmdasha casestudyrdquo IEEE Transactions on Power Electronics vol 28 no 6pp 2998ndash3007 2013
[23] H Wang M Liserre and F Blaabjerg ldquoToward reliable powerelectronics challenges design tools and opportunitiesrdquo IEEEIndustrial Electronics Magazine vol 7 no 2 pp 17ndash26 2013
[24] H Huang and P A Mawby ldquoA lifetime estimation techniquefor voltage source invertersrdquo IEEE Transactions on PowerElectronics vol 28 no 8 pp 4113ndash4119 2013
[25] P McCluskey ldquoReliability of power electronics under thermalloadingrdquo in Proceedings of the 7th International Conference onIntegrated Power Electronics Systems (CIPS rsquo12) March 2012
10 International Journal of Photoenergy
[26] H Lu C Bailey and C Yin ldquoDesign for reliability of powerelectronics modulesrdquoMicroelectronics Reliability vol 49 no 9ndash11 pp 1250ndash1255 2009
[27] M Ciappa ldquoLifetime prediction on the base ofmission profilesrdquoMicroelectronics Reliability vol 45 no 9-11 pp 1293ndash1298 2005
[28] F Chan and H Calleja ldquoReliability estimation of three single-phase topologies in grid-connected PV systemsrdquo IEEE Trans-actions on Industrial Electronics vol 58 no 7 pp 2683ndash26892011
[29] K Ma M Liserre F Blaabjerg and T Kerekes ldquoThermalloading and lifetime estimation for power device consideringmission profiles in wind power converterrdquo IEEE Transactionson Power Electronics vol 30 no 2 pp 590ndash602 2015
[30] S Harb and R S Balog ldquoReliability of candidate pho-tovoltaic module-integrated-inverter (PV-MII) topologiesmdashausagemodel approachrdquo IEEE Transactions on Power Electronicsvol 28 no 6 pp 3019ndash3027 2013
[31] P Zhang YWangW Xiao andW Li ldquoReliability evaluation ofgrid-connected photovoltaic power systemsrdquo IEEETransactionson Sustainable Energy vol 3 no 3 pp 379ndash389 2012
[32] S E De Leon-Aldaco H Calleja and J Aguayo ldquoReliability andmission profiles of photovoltaic systems a FIDES approachrdquoIEEE Transactions on Power Electronics vol 30 no 5 pp 2578ndash2586 2015
[33] S B Kjaer J K Pedersen and F Blaabjerg ldquoA review of single-phase grid-connected inverters for photovoltaicmodulesrdquo IEEETransactions on Industry Applications vol 41 no 5 pp 1292ndash1306 2005
[34] H Li J PengW Liu Z Huang andK-C Lin ldquoA newton-basedextremumseekingMPPTmethod for photovoltaic systemswithstochastic perturbationsrdquo International Journal of Photoenergyvol 2014 Article ID 938526 13 pages 2014
[35] D Sera L Mathe T Kerekes S V Spataru and R TeodoresculdquoOn the perturb-and-observe and incremental conductancemppt methods for PV systemsrdquo IEEE Journal of Photovoltaicsvol 3 no 3 pp 1070ndash1078 2013
[36] M Abdulkadir A H M Yatim and S T Yusuf ldquoAn improvedPSO-based MPPT control strategy for photovoltaic systemsrdquoInternational Journal of Photoenergy vol 2014 Article ID818232 11 pages 2014
[37] Y Zhou and H Li ldquoAnalysis and suppression of leakage cur-rent in cascaded-multilevel-inverter-based PV systemsrdquo IEEETransactions on Power Electronics vol 29 no 10 pp 5265ndash52772014
[38] A Hajiah T Khatib K Sopian and M Sebzali ldquoPerformanceof grid-connected photovoltaic system in two sites in KuwaitrdquoInternational Journal of Photoenergy vol 2012 Article ID178175 7 pages 2012
[39] M Musallam C Yin C Bailey and M Johnson ldquoMissionprofile-based reliability design and real-time life consumptionestimation in power electronicsrdquo IEEE Transactions on PowerElectronics vol 30 no 5 pp 2601ndash2613 2015
[40] Y Yang HWang F Blaabjerg and T Kerekes ldquoA hybrid powercontrol concept for PV inverters with reduced thermal loadingrdquoIEEE Transactions on Power Electronics vol 29 no 12 pp 6271ndash6275 2014
[41] A T Bryant P A Mawby P R Palmer E Santi and J LHudgins ldquoExploration of power device reliability using com-pact device models and fast electrothermal simulationrdquo IEEETransactions on Industry Applications vol 44 no 3 pp 894ndash903 2008
[42] M Musallam and C M Johnson ldquoAn efficient implementationof the rainflow counting algorithm for life consumption estima-tionrdquo IEEE Transactions on Reliability vol 61 no 4 pp 978ndash986 2012
[43] Plexim Gmbh ldquoPLECSmdashthe simulation platform for powerelectronics systemsrdquo Workshop Documentation 1 Aalborg2014
[44] I F Kovacevic U Drofenik and J W Kolar ldquoNew physicalmodel for lifetime estimation of powermodulesrdquo in Proceedingsof the International Power Electronics Conference (IPEC rsquo10) pp2106ndash2114 Sapporo Japan June 2010
[45] C Busca R Teodorescu F Blaabjerg et al ldquoAn overview ofthe reliability prediction related aspects of high power IGBTsin wind power applicationsrdquoMicroelectronics Reliability vol 51no 9ndash11 pp 1903ndash1907 2011
[46] ABB ldquoApplication NotemdashApplying IGBTsrdquo 2014 httpwwwabbcom
[47] A Volke and M Hornkamp IGBT ModulesmdashTechnologiesDriver and Application Infineon Technologies AG MunichGermany 2012
[48] U Scheuermann ldquoReliability of advanced power modules forextended maximum junction temperaturesrdquo Bodorsquos Power Sys-tems pp 26ndash30 2014
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 9
converters In a word the reliability assessment in this paperreveals that much attention has to be put on the thermaldesign of the critical components in an entire PV inverter inorder to reduce the cost of energy
5 Conclusions
In this paper a qualitative reliability assessment of threeselected single-phase transformerless PV inverters has beencarried out in accordance with a mission profile based reli-ability analysis approach A real-field yearly mission profilehas been applied to the selected transformerless candidatesfor the reliability assessment The comparison results haverevealed that although minimizing leakage currents as wellas maintaining a satisfactory efficiency has been targetedby those inverters the extra devices that are used fordisconnection of the PV panels or the PV inverters mightbe heated up during operation The high thermal loadingwill further induce failures of the power switching devicesbeing a big challenge to the entire system reliability As aconsequence many efforts should be devoted to a reliability-oriented design of the critical components in a PV inverterand thus a reduced cost of energy can be achieved
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] F Blaabjerg K Ma and Y Yang ldquoPower electronicsmdashthe keytechnology for renewable energy systemsrdquo in Proceedings ofthe 9th International Conference on Ecological Vehicles andRenewable Energies (EVER rsquo14) pp 1ndash11 Monte-Carlo MonacoMarch 2014
[2] 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
[3] J M Carrasco L G Franquelo J T Bialasiewicz et al ldquoPower-electronic systems for the grid integration of renewable energysources a surveyrdquo IEEE Transactions on Industrial Electronicsvol 53 no 4 pp 1002ndash1016 2006
[4] J D vanWyk and F C Lee ldquoOn a future for power electronicsrdquoIEEE Journal of Emerging and Selected Topics in Power Electron-ics vol 1 no 2 pp 59ndash72 2013
[5] A Golnas ldquoPV system reliability an operatorrsquos perspectiverdquoIEEE Journal of Photovoltaics vol 3 no 1 pp 416ndash421 2013
[6] A Ristow M Begovic A Pregelj and A Rohatgi ldquoDevelop-ment of a methodology for improving photovoltaic inverterreliabilityrdquo IEEE Transactions on Industrial Electronics vol 55no 7 pp 2581ndash2592 2008
[7] E Romero-Cadaval G Spagnuolo L G Franquelo C ARamos-Paja T Suntio and W M Xiao ldquoGrid-connectedphotovoltaic generation plants components and operationrdquoIEEE Industrial ElectronicsMagazine vol 7 no 3 pp 6ndash20 2013
[8] REN21 ldquoRenewables 2014 global status reportrdquo Tech Rep 2014httpwwwren21net
[9] M Liserre T Sauter and J Y Hung ldquoFuture energy systemsintegrating renewable energy sources into the smart power
grid through industrial electronicsrdquo IEEE Industrial ElectronicsMagazine vol 4 no 1 pp 18ndash37 2010
[10] C-L Shen and S-H Yang ldquoMulti-input converter with MPPTfeature for wind-PV power generation systemrdquo InternationalJournal of Photoenergy vol 2013 Article ID 129254 13 pages2013
[11] F Blaabjerg and K Ma ldquoFuture on power electronics for windturbine systemsrdquo IEEE Journal of Emerging and Selected Topicsin Power Electronics vol 1 no 3 pp 139ndash152 2013
[12] R TeodorescuM Liserre and P RodriguezGrid Converters forPhotovoltaic and Wind Power Systems Wiley-IEEE Press 2011
[13] R Gonzalez J Lopez P Sanchis and L Marroyo ldquoTrans-formerless inverter for single-phase photovoltaic systemsrdquo IEEETransactions on Power Electronics vol 22 no 2 pp 693ndash6972007
[14] H Schmidt C Siedle and J Ketterer ldquoDCAC converter toconvert direct electric voltage into alternating voltage or intoalternating currentrdquo US Patent 7046534 2006
[15] T Kerekes M Liserre R Teodorescu C Klumpner and MSumner ldquoEvaluation of three-phase transformerless photo-voltaic inverter topologiesrdquo IEEE Transactions on Power Elec-tronics vol 24 no 9 pp 2202ndash2211 2009
[16] R Gonzalez E Gubıa J Lopez and L Marroyo ldquoTransformer-less single-phase multilevel-based photovoltaic inverterrdquo IEEETransactions on Industrial Electronics vol 55 no 7 pp 2694ndash2702 2008
[17] Advanced Energy ldquoWhatrsquos ahead for PV inverter technologyrdquoGreentechsolar 2014 httpwwwgreentechmediacom
[18] I Patrao E Figueres F Gonzalez-Espın and G GarceraldquoTransformerless topologies for grid-connected single-phasephotovoltaic invertersrdquo Renewable and Sustainable EnergyReviews vol 15 no 7 pp 3423ndash3431 2011
[19] N Achilladelis E Koutroulis and F Blaabjerg ldquoOptimizedpulse width modulation for transformerless active-NPC invert-ersrdquo in Proceedings of the 16th European Conference on PowerElectronics and Applications (EPE rsquo14-ECCE Europe) pp 1ndash10Lappeenranta Finland August 2014
[20] S Saridakis E Koutroulis and F Blaabjerg ldquoOptimal design ofmodern transformerless PV inverter topologiesdrdquo IEEE Trans-actions on Energy Conversion vol 28 no 2 pp 394ndash404 2013
[21] Y Yang H Wang F Blaabjerg and K Ma ldquoMission profilebased multi-disciplinary analysis of power modules in single-phase transformerless photovoltaic invertersrdquo in Proceedingsof the 15th European Conference on Power Electronics andApplications (EPE rsquo13) pp 1ndash10 IEEE Lille France September2013
[22] S E de Leon-Aldaco H Calleja F Chan and H R Jimenez-Grajales ldquoEffect of the mission profile on the reliability of apower converter aimed at photovoltaic applicationsmdasha casestudyrdquo IEEE Transactions on Power Electronics vol 28 no 6pp 2998ndash3007 2013
[23] H Wang M Liserre and F Blaabjerg ldquoToward reliable powerelectronics challenges design tools and opportunitiesrdquo IEEEIndustrial Electronics Magazine vol 7 no 2 pp 17ndash26 2013
[24] H Huang and P A Mawby ldquoA lifetime estimation techniquefor voltage source invertersrdquo IEEE Transactions on PowerElectronics vol 28 no 8 pp 4113ndash4119 2013
[25] P McCluskey ldquoReliability of power electronics under thermalloadingrdquo in Proceedings of the 7th International Conference onIntegrated Power Electronics Systems (CIPS rsquo12) March 2012
10 International Journal of Photoenergy
[26] H Lu C Bailey and C Yin ldquoDesign for reliability of powerelectronics modulesrdquoMicroelectronics Reliability vol 49 no 9ndash11 pp 1250ndash1255 2009
[27] M Ciappa ldquoLifetime prediction on the base ofmission profilesrdquoMicroelectronics Reliability vol 45 no 9-11 pp 1293ndash1298 2005
[28] F Chan and H Calleja ldquoReliability estimation of three single-phase topologies in grid-connected PV systemsrdquo IEEE Trans-actions on Industrial Electronics vol 58 no 7 pp 2683ndash26892011
[29] K Ma M Liserre F Blaabjerg and T Kerekes ldquoThermalloading and lifetime estimation for power device consideringmission profiles in wind power converterrdquo IEEE Transactionson Power Electronics vol 30 no 2 pp 590ndash602 2015
[30] S Harb and R S Balog ldquoReliability of candidate pho-tovoltaic module-integrated-inverter (PV-MII) topologiesmdashausagemodel approachrdquo IEEE Transactions on Power Electronicsvol 28 no 6 pp 3019ndash3027 2013
[31] P Zhang YWangW Xiao andW Li ldquoReliability evaluation ofgrid-connected photovoltaic power systemsrdquo IEEETransactionson Sustainable Energy vol 3 no 3 pp 379ndash389 2012
[32] S E De Leon-Aldaco H Calleja and J Aguayo ldquoReliability andmission profiles of photovoltaic systems a FIDES approachrdquoIEEE Transactions on Power Electronics vol 30 no 5 pp 2578ndash2586 2015
[33] S B Kjaer J K Pedersen and F Blaabjerg ldquoA review of single-phase grid-connected inverters for photovoltaicmodulesrdquo IEEETransactions on Industry Applications vol 41 no 5 pp 1292ndash1306 2005
[34] H Li J PengW Liu Z Huang andK-C Lin ldquoA newton-basedextremumseekingMPPTmethod for photovoltaic systemswithstochastic perturbationsrdquo International Journal of Photoenergyvol 2014 Article ID 938526 13 pages 2014
[35] D Sera L Mathe T Kerekes S V Spataru and R TeodoresculdquoOn the perturb-and-observe and incremental conductancemppt methods for PV systemsrdquo IEEE Journal of Photovoltaicsvol 3 no 3 pp 1070ndash1078 2013
[36] M Abdulkadir A H M Yatim and S T Yusuf ldquoAn improvedPSO-based MPPT control strategy for photovoltaic systemsrdquoInternational Journal of Photoenergy vol 2014 Article ID818232 11 pages 2014
[37] Y Zhou and H Li ldquoAnalysis and suppression of leakage cur-rent in cascaded-multilevel-inverter-based PV systemsrdquo IEEETransactions on Power Electronics vol 29 no 10 pp 5265ndash52772014
[38] A Hajiah T Khatib K Sopian and M Sebzali ldquoPerformanceof grid-connected photovoltaic system in two sites in KuwaitrdquoInternational Journal of Photoenergy vol 2012 Article ID178175 7 pages 2012
[39] M Musallam C Yin C Bailey and M Johnson ldquoMissionprofile-based reliability design and real-time life consumptionestimation in power electronicsrdquo IEEE Transactions on PowerElectronics vol 30 no 5 pp 2601ndash2613 2015
[40] Y Yang HWang F Blaabjerg and T Kerekes ldquoA hybrid powercontrol concept for PV inverters with reduced thermal loadingrdquoIEEE Transactions on Power Electronics vol 29 no 12 pp 6271ndash6275 2014
[41] A T Bryant P A Mawby P R Palmer E Santi and J LHudgins ldquoExploration of power device reliability using com-pact device models and fast electrothermal simulationrdquo IEEETransactions on Industry Applications vol 44 no 3 pp 894ndash903 2008
[42] M Musallam and C M Johnson ldquoAn efficient implementationof the rainflow counting algorithm for life consumption estima-tionrdquo IEEE Transactions on Reliability vol 61 no 4 pp 978ndash986 2012
[43] Plexim Gmbh ldquoPLECSmdashthe simulation platform for powerelectronics systemsrdquo Workshop Documentation 1 Aalborg2014
[44] I F Kovacevic U Drofenik and J W Kolar ldquoNew physicalmodel for lifetime estimation of powermodulesrdquo in Proceedingsof the International Power Electronics Conference (IPEC rsquo10) pp2106ndash2114 Sapporo Japan June 2010
[45] C Busca R Teodorescu F Blaabjerg et al ldquoAn overview ofthe reliability prediction related aspects of high power IGBTsin wind power applicationsrdquoMicroelectronics Reliability vol 51no 9ndash11 pp 1903ndash1907 2011
[46] ABB ldquoApplication NotemdashApplying IGBTsrdquo 2014 httpwwwabbcom
[47] A Volke and M Hornkamp IGBT ModulesmdashTechnologiesDriver and Application Infineon Technologies AG MunichGermany 2012
[48] U Scheuermann ldquoReliability of advanced power modules forextended maximum junction temperaturesrdquo Bodorsquos Power Sys-tems pp 26ndash30 2014
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
10 International Journal of Photoenergy
[26] H Lu C Bailey and C Yin ldquoDesign for reliability of powerelectronics modulesrdquoMicroelectronics Reliability vol 49 no 9ndash11 pp 1250ndash1255 2009
[27] M Ciappa ldquoLifetime prediction on the base ofmission profilesrdquoMicroelectronics Reliability vol 45 no 9-11 pp 1293ndash1298 2005
[28] F Chan and H Calleja ldquoReliability estimation of three single-phase topologies in grid-connected PV systemsrdquo IEEE Trans-actions on Industrial Electronics vol 58 no 7 pp 2683ndash26892011
[29] K Ma M Liserre F Blaabjerg and T Kerekes ldquoThermalloading and lifetime estimation for power device consideringmission profiles in wind power converterrdquo IEEE Transactionson Power Electronics vol 30 no 2 pp 590ndash602 2015
[30] S Harb and R S Balog ldquoReliability of candidate pho-tovoltaic module-integrated-inverter (PV-MII) topologiesmdashausagemodel approachrdquo IEEE Transactions on Power Electronicsvol 28 no 6 pp 3019ndash3027 2013
[31] P Zhang YWangW Xiao andW Li ldquoReliability evaluation ofgrid-connected photovoltaic power systemsrdquo IEEETransactionson Sustainable Energy vol 3 no 3 pp 379ndash389 2012
[32] S E De Leon-Aldaco H Calleja and J Aguayo ldquoReliability andmission profiles of photovoltaic systems a FIDES approachrdquoIEEE Transactions on Power Electronics vol 30 no 5 pp 2578ndash2586 2015
[33] S B Kjaer J K Pedersen and F Blaabjerg ldquoA review of single-phase grid-connected inverters for photovoltaicmodulesrdquo IEEETransactions on Industry Applications vol 41 no 5 pp 1292ndash1306 2005
[34] H Li J PengW Liu Z Huang andK-C Lin ldquoA newton-basedextremumseekingMPPTmethod for photovoltaic systemswithstochastic perturbationsrdquo International Journal of Photoenergyvol 2014 Article ID 938526 13 pages 2014
[35] D Sera L Mathe T Kerekes S V Spataru and R TeodoresculdquoOn the perturb-and-observe and incremental conductancemppt methods for PV systemsrdquo IEEE Journal of Photovoltaicsvol 3 no 3 pp 1070ndash1078 2013
[36] M Abdulkadir A H M Yatim and S T Yusuf ldquoAn improvedPSO-based MPPT control strategy for photovoltaic systemsrdquoInternational Journal of Photoenergy vol 2014 Article ID818232 11 pages 2014
[37] Y Zhou and H Li ldquoAnalysis and suppression of leakage cur-rent in cascaded-multilevel-inverter-based PV systemsrdquo IEEETransactions on Power Electronics vol 29 no 10 pp 5265ndash52772014
[38] A Hajiah T Khatib K Sopian and M Sebzali ldquoPerformanceof grid-connected photovoltaic system in two sites in KuwaitrdquoInternational Journal of Photoenergy vol 2012 Article ID178175 7 pages 2012
[39] M Musallam C Yin C Bailey and M Johnson ldquoMissionprofile-based reliability design and real-time life consumptionestimation in power electronicsrdquo IEEE Transactions on PowerElectronics vol 30 no 5 pp 2601ndash2613 2015
[40] Y Yang HWang F Blaabjerg and T Kerekes ldquoA hybrid powercontrol concept for PV inverters with reduced thermal loadingrdquoIEEE Transactions on Power Electronics vol 29 no 12 pp 6271ndash6275 2014
[41] A T Bryant P A Mawby P R Palmer E Santi and J LHudgins ldquoExploration of power device reliability using com-pact device models and fast electrothermal simulationrdquo IEEETransactions on Industry Applications vol 44 no 3 pp 894ndash903 2008
[42] M Musallam and C M Johnson ldquoAn efficient implementationof the rainflow counting algorithm for life consumption estima-tionrdquo IEEE Transactions on Reliability vol 61 no 4 pp 978ndash986 2012
[43] Plexim Gmbh ldquoPLECSmdashthe simulation platform for powerelectronics systemsrdquo Workshop Documentation 1 Aalborg2014
[44] I F Kovacevic U Drofenik and J W Kolar ldquoNew physicalmodel for lifetime estimation of powermodulesrdquo in Proceedingsof the International Power Electronics Conference (IPEC rsquo10) pp2106ndash2114 Sapporo Japan June 2010
[45] C Busca R Teodorescu F Blaabjerg et al ldquoAn overview ofthe reliability prediction related aspects of high power IGBTsin wind power applicationsrdquoMicroelectronics Reliability vol 51no 9ndash11 pp 1903ndash1907 2011
[46] ABB ldquoApplication NotemdashApplying IGBTsrdquo 2014 httpwwwabbcom
[47] A Volke and M Hornkamp IGBT ModulesmdashTechnologiesDriver and Application Infineon Technologies AG MunichGermany 2012
[48] U Scheuermann ldquoReliability of advanced power modules forextended maximum junction temperaturesrdquo Bodorsquos Power Sys-tems pp 26ndash30 2014
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of