IET Electric Power Applications

Research Article

Experimental verification of windingswitching technique to enhance maximumspeed operation of surface mountedpermanent magnet machines

IET Electr. Power Appl., 2016294 & The Institution of Engine

ISSN 1751-8660Received on 1st July 2015Revised on 25th August 2015Accepted on 13th October 2015doi: 10.1049/iet-epa.2015.0274www.ietdl.org

Shahid Atiq1, Thomas A. Lipo2, Byung-il Kwon1 ✉

1Department of Electronic Systems Engineering, Hanyang University, Ansan 426-791, South Korea2Department of Electrical and Computer Engineering, Florida State University, Tallahassee Fl 32310, USA

✉ E-mail: bikwon@hanyang.ac.kr

Abstract: Flux weakening is an inevitable requirement in the operation of variable speed permanent magnet (PM)machines for high-speed applications due to inverter voltage limits. A new winding switching technique isexperimentally validated in this study that can extend the speed range of such PM machines. A drive topology isproposed that utilises two current regulated voltage source inverters to control the machine in a dual inverter fedconfiguration before transitioning into an open winding configuration after winding switching. The proposed drivetopology extends the constant torque region of the machine and boosts its maximum output power capability.Complete experimental results are provided to demonstrate the effectiveness of the proposed machine drive systemfor continuous operation over the entire speed range.

1 Introduction

Permanent magnet (PM) machines are being widely used in industrydue to their favourable characteristics, which include high powerdensity, high torque to inertia ratio, high power factor, betterefficiency, and the absence of external excitation circuits.However, the maximum speed of these machines is limited by theability of the inverter voltages to inject the proper currents into themachine windings due to increasing back EMF. Many solutionshave been proposed in the literature to extend the maximum speedof PM machines. For example, conventional vector control is usedto inject a negative d-axis current to weaken the PM flux linkage,which limits the back EMF of the machine. However, negatived-axis current injection also has a limitation in reducing the airgap flux due to constraints on machine structure, losses and risk ofpossible irreversible demagnetisation of PMs. A minimum copperloss flux weakening technique was presented in [1] where theoutput voltage vector was continuously matched with themaximum output voltage vector allowed by the inverter.Instantaneous power theory was adopted in [2] whereinstantaneous real and imaginary components of the power werecontrolled to achieve flux weakening. A direct torque controlstrategy was used in [3] to control the torque and stator fluxlinkages for interior permanent magnet machines. Sudhoff et al.[4], and Soong et al. [5] discussed machine design issues usingconcentrated windings to enhance the field weakening capabilityof surface-mounted permanent magnet (SMPM) machines. Theflux weakening capability of distributed and concentrated machinewindings were compared in [6], and it was concluded thatconcentrated windings provide better field weakening capabilitycompared with distributed windings. However, it was alsodetermined that distributed windings best utilise inverter voltagesat the base speed. A stator mounted PM machine was presented in[7], where field weakening was achieved by changing thereluctance path.

Pole changing induction machines, as well as PM machines, wereproposed in [8–12] to enhance the maximum speed capability. Inthese studies, low-speed operation of the machine utilised highpole numbers and high-speed operation of the machine utilisedlow pole numbers. Electronic pole changing was used to enhance

the speed of an induction machine by changing it from a four-poleto a two-pole configuration [8]. Conversion of a 12-polethree-phase induction machine to a four-pole nine-phaseconfiguration was presented in [9]. A dual inverter fed six phasepole changing machine was presented in [10]. Therein, polechanging was achieved by controlling the angle of PWM carriersand references for four-pole and two-pole operation. A polechanging PM motor based on a memory motor rotor design wasdescribed in [11]. A consequent pole changing PM machine withtwo flux sources, that is, a PM on the rotor of the machine and afield coil placed on the stator of the machine, was presented in [12].

Winding switching has been shown to be an alternate means toextend the maximum speed of the machines [13–17]. The basicidea behind increasing the speed of the machine by windingswitching in [13–15] is to utilise wye, delta, series, and parallelconnections in the stator windings. Normally, wye and seriesconnections are used for low-speed operations, and delta andparallel connections are used for high-speed operation [14].Connections from low speed to high-speed operation are listed aswye in series, delta in series, wye in parallel and delta in parallelin [15]. A novel winding switching alternative to star-delta orseries-parallel connections was presented in [16, 17], where themain machine windings were divided in two equal sub-windings.These two sub-windings were controlled either to generate additiveMMF or switched to generate subtractive MMF for fluxweakening. However, no experimental results to validate theproposed field weakening technique have yet been presented. Inaddition, no suitable drive system that utilises this kind of windingswitching has been proposed in the literature. Hence, successfulwinding switching from normal operation to the field weakeningregion and back during continuous operation is still questionablebecause of a lack of experimental verification of this technique. Asimulation based drive topology for this field weakening techniquewas recently presented in [18]. This topology divides the operationof the machine into three regions, namely low speed, mediumspeed and high-speed. However, this drive topology is inefficientin terms of hardware utilisation and maximum achievable speed ofthe machine. In this topology, one of the two inverters remainsidle during low-speed operation, whereas one inverter and half ofthe machine windings remain idle during high-speed operation.

, Vol. 10, Iss. 4, pp. 294–303ering and Technology 2016

Only the medium speed range utilises the full hardware of the motordrive system. Moreover, two extra switches (besides a thyristor andsix diodes required for winding switching) are also involved that addextra hardware to the system and add extra switching transients to themachine operation.

This paper not only presents the experimental verification of thefield weakening technique using winding switching but alsoproposes a new suitable drive topology that extends the constantpower region of the machine as well as boosts the maximumpower capability of the machine. Successful transition during thewinding switching process is experimentally demonstrated. Theproposed drive topology uses two current regulated voltage sourceinverters (CRVSIs) to control the machine and utilises the benefitsof a dual inverter fed machine configuration [19] as well as a dualinverter fed open winding machine configuration [20]. Theremainder of the paper is organised as follows. Section 2, presentsan overview of the winding switching concept. This is followed bySection 3, which contains a mathematical analysis of the machinemodels proposed in this paper. Section 4, presents the proposeddrive topology, while detailed experimental results for all possiblecases of the machine operation are presented in Section 5. Asummary of the overall research work is provided in the conclusion.

2 Winding switching topology

The basic three phase winding of the machine shown in Fig. 1a isdivided into two equal sub-windings (ABC and XYZ in [16, 17]),and a central neutral connection is established using severalelectronic switches. The current entering from the dotted ends ofthe windings produces a positive MMF, while current leaving thedotted ends of the windings produces a negative MMF. Currentsfrom two inverters in Fig. 1b are controlled to enter at the dottedends of both windings, and this produces a net air gap flux equalto the basic three phase machine. In the next step, electronicswitches used to establish a common neutral are turned off, andthe two inverters are used to inject current at the dotted end fromone side of the machine winding; this current leaves at the dottedend of the other side of the machine, as shown in Fig. 1c. In thiscase, the flux of winding XYZ is subtracted from the flux ofwinding ABC, and a net reduction in overall air gap flux isachieved during this process.

3 Proposed machine models

The basic three phase machine model being investigated in this paperis a four pole 24 slot machine with a distributed double layer windingwhere each slot is electrically displaced by π/6 rad. The winding ofthe machine is divided into two equal half windings, wherein thesewindings can be electrically displaced by π/6 rad or π/3 rad.Fig. 2a shows a machine model where windings ABC and XYZhave a displacement of two slots, resulting in π/3 rad electricallyphase shifted windings. Fig. 2b shows a π/6 rad electrically phaseshifted winding configuration where windings ABC and XYZ areplaced with one slot displacement. The designations model-I andmodel-II will be used to refer to these two machine configurationsin the remainder of this paper.

The back EMF for the two models is given in (1)–(3) for phases Aand X of the machine.

Ea = E sin vet( )

(1)

Ex1 = E sin vet − p/3( )

(2)

Ex2 = E sin vet − p/6( )

(3)

Here, Ea, Ex1 and Ex2 are the back EMF of phases A and X formodel-I, and X for model-II, respectively, E is the magnitude ofthe back EMF and ωe is the electrical angular velocity. The netadditive EMF of the machine, Eadd, and the subtractive EMF of

IET Electr. Power Appl., 2016, Vol. 10, Iss. 4, pp. 294–303& The Institution of Engineering and Technology 2016

the machine, Esub, are given by (4)–(7) before and after windingswitching for the two models.

Eadd1 = E sin vet( )+ E sin vet − p/3

( )

Eadd1 = 1.7320E sin vet − p/6( ) (4)

Esub1 = E sin vet( )− E sin vet − p/3

( )

Esub1 = E sin vet + p/3( ) (5)

Eadd2 = 1.9319E sin vet − p/12( )

(6)

Esub2 = 0.5176E sin vet + 5p/12( )

(7)

The net field weakening (Ews) due to winding switching is the ratioof the additive EMF of the machine before winding switching to thesubtractive EMF of the machine after winding switching. Ews1 andEws2 are the net field weakening values for the two machinemodels, which are given in (8) and (9), respectively.

Ews1 =Eadd1

Esub1

∣∣∣∣∣∣∣∣ = 1.7320 (8)

Ews2 =Eadd2

Esub2

∣∣∣∣∣∣∣∣ = 3.7324 (9)

This very simple analysis provides all the information necessary todescribe winding switching over the whole speed range of themachine, and the analysis can be summarised as follows:

(i) Upon winding switching, the net flux of the machine is reducedby a factor of 1.7320 for model-I and 3.7324 for model-II.(ii) The net additive EMF of the machine lags phase A by an angleof π/6 for model-I and π/12 for model-II.(iii) The net subtractive EMF of the machine leads phase A by anangle of π/3 for model-I and 5π/12 for model-II.

4 Proposed drive topology

The novel drive topology proposed in this paper utilises two CRVSIsat both ends of the machine windings. Machine operation can bedivided into two operating regions: (i) normal flux operationbefore winding switching and (ii) reduced flux operation afterwinding switching. The operating strategies for these regions aredescribed below.

4.1 Operating strategy before winding switching

Initially, the machine is operated as a dual inverter fed three phasemachine with two CRVIs that control the currents through two setsof windings ABC and XYZ. However, when the machine isoperated with dual three-phase windings using two voltage sourceinverters, an unbalanced current sharing problem can occurbetween the two sets of windings. This problem is due to eitherasymmetries between the two sets of windings or asymmetricaloperation of the two inverters [21]. Several methods have beenproposed to deal with the unbalanced current sharing problem. Astationary frame current regulator was used in conjunction withspace vector decomposition [19] to handle the unbalanced currentsharing problem between the two power sections of the machine.Zhao and Lipo [22] adopted a space vector decomposition methodto remove the harmonic contents in the three phase currents of adual inverter fed induction machine.

Unlike induction machines, PM machines do not have slipproblems. However, asymmetries in PM machine parameters orinverter control can create an asymmetrical current sharingproblem. Karttunen et al. [23] demonstrated unbalanced operationof a PM machine and proposed a control strategy to balancecurrent sharing between two sets of machine windings. Otherinvestigators [24] demonstrated imbalanced operation of a dualinverter fed PM machine using asymmetrical dead time.

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Fig. 1 Machine winding configuration

a Basic three phaseb Before winding switchingc After winding switching

Problems associated with common mode voltages and circulatingcurrents can also occur in dual inverter fed machines [25–27].Somasekhar et al. [26], and Rama Chandra Sekhar and Srinivas[27] used separate Vdc sources for the two side inverters toovercome these problems. Six PI regulators were used in [28] tocontrol the Idq0 components of the two sets of three-phasewindings of a dual inverter fed induction machine. Six PI currentregulators in the synchronous frame are implemented in this paperto control Idq01 and Idq02 currents to ensure symmetrical currents intwo machine windings and avoid steady state error problems of thestationary frame current regulators [29]. To overcome commonmode circulating currents separate DC sources have been used inthe experiment. Moreover, since the neutral of the two three-phasewindings are connected together, a current controller to limit zero

Fig. 2 Winding placement in the stator before and after winding switching

a Model-Ib Model-II

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sequence currents has also been implemented in addition to d-axisand q-axis current controllers to ensure balanced three phasecurrents. Fig. 3a shows a block diagram of a machine controlsystem that employs synchronous frame current regulators.

When a machine is converted from a three phase to a six phaseconfiguration, the phase back EMF of the machine is reduced by afactor of 1.73 for model-I and 1.93 for model-II as calculatedusing (1) and (4), and (1) and (6), respectively. This suggests thatan extra terminal voltage is available to increase the speed of themachine beyond 1 p.u due to the reduced back EMF of a six phasemachine configuration. The increase in speed will result in higherpower at constant torque. However, there is an additional voltagedrop due to mutual inductance coupling of winding ABC withwinding XYZ and vice versa, (10). This voltage drop will impose a

IET Electr. Power Appl., 2016, Vol. 10, Iss. 4, pp. 294–303& The Institution of Engineering and Technology 2016

Fig. 3 Proposed drive topology

a Current regulators in synchronous frameb Torque, speed and currents of the proposed drive topology over the entire speed range

limit on the speed extension during six phase operation of themachine. This extended speed operation at constant torque is amachine characteristic that depends upon its parameters.

Va = Ea + Ria + Ladiadt

+ Labdibdt

+ Lacdicdt

+ Laxdixdt

+ Laydiydt

+ Lazdizdt

(10)

To operate in a flux weakening configuration, the calculated machinewinding switching points are 1.73 for model-I and 3.73 for model-II.Therefore, to maintain a constant rated power during windingswitching, the machine should be operating at a speed of 1.73 p.uwith a torque of 1/1.73 p.u for model-I and a speed of 3.73 p.uwith a torque of 1/3.73 p.u for model-II. To ensure smoothwinding switching with minimum transients, the torque ofthe machine just before and just after winding switching must bethe same.

IET Electr. Power Appl., 2016, Vol. 10, Iss. 4, pp. 294–303& The Institution of Engineering and Technology 2016

The current control strategy for the proposed machine operation isgiven in Fig. 3b. The machine is started with Id = 0 control until itreaches the rated speed and torque operation of the basic threephase machine, indicated by point a on the power curve shown inFig. 3b. Since additional voltage is available, the machine is ableto continue increasing speed with constant torque until point b.Operation of the machine from point a to point d is dependent onthe machine parameters. There is no need to apply a negatived-axis current if the machine is able to reach the windingswitching speed (nws) utilising the extra voltage. In this case,point b occurs at nws, and operation between point b and point ddoes not occur. However, if the machine cannot achieve nwsutilising the extra voltage, a negative d-axis current must beapplied to increase the speed further from point b to point d inorder to reach one per unit power at nws. By definition, thisincrease in speed using a negative d-axis current depends upon therelative size of E against XdId. Here, E is the back EMF of themachine, Xd is the d-axis reactance, and Id is d-axis current. Thepower of the machine could remain constant in the speed range

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Table 1 Maximum achievable speed of the machine

Machinemodel

Windingswitching point

Maximum achievablespeed, p.u

Angleadjustment, rad

I 1.73 2.99 p/3II 3.73 6.46 5p/12

between point b and point d and machine operation could move frompoint b to point c. However, in order to reduce the power to 1 p.u forsmooth winding switching, the machine must be intentionallycontrolled on path b to d rather than path b to c. This alsosuggests that machine should have inherent capability to achievenws by maintaining at least 1 p.u power so that machine could beoperated with a minimum of one p.u power for the entire speedrange.

4.2 Operation strategy after winding switching

When the machine reaches nws, the thyristors, which provide thecentral neutral connection, are turned off and the machine operatesin the field weakening region with an open winding configurationas shown in Fig. 1c. At this point negative d-axis current if any, isremoved and the machine is again operating in a constant torqueregion with unity internal power factor. This operating regionprovides both flux weakening without a negative d-axis currentand higher voltages (by a factor of

√3) at the terminals of the

machine due to the open winding configuration [20, 30]. Linevoltages in star connected machines appear as phase voltages in anopen windings configuration. Hence, the machine speed can beincreased further by

√3 times the winding switching point speed

at constant torque, according to (11).

nfinal =√3× nws (11)

Here, nfinal is the final achievable speed of the machine.The machine is assumed to operate at one p.u power at the instant

when winding switching occurs. Therefore, the machine will alsoachieve a final power of

√3 times the rated power of the machine.

Currents through the windings of the machine are maintainedwithin the rated current limits according to (12) over entire speedrange of the machine.

Is ≤����������Iq

2 + Id2

√(12)

Here, Is is the rated current of the basic three phase machine.It is important to note that the back EMF angle also changes

during winding switching operation. To inject currents in phasewith the back EMF, this angle adjustment should be made in thesoftware to achieve Id = 0 current control after winding switching.Table 1 provides the final achievable speed of the machine withthis proposed control strategy and the angle adjustments requiredduring this mode of operation for both machine models.

4.3 Gating signal generation for the two inverters

Three phase currents Iabc and Ixyz are measured at the motorterminals. These are converted into two phase stationary frame ofreference using (13) and (14).

Ia1Ib1

I01

⎡⎢⎣

⎤⎥⎦ =

1 0 00 1

/√3 −1

/√3

1/3 1/3 1/3

⎡⎣

⎤⎦

IaIbIc

⎡⎣

⎤⎦ (13)

Ia2Ib2

I02

⎡⎢⎣

⎤⎥⎦ =

1 0 00 1

/√3 −1

/√3

1/3 1/3 1/3

⎡⎣

⎤⎦

IxIxIz

⎡⎣

⎤⎦ (14)

298

These stationary frame currents are now transformed intosynchronous frame currents Idq01 and Idq02 using (15) and (16)where θe is rotor angle and δ is the angle between the twowindings ABC and XYZ assuming phase-A axis at zero referenceangle. Note that δ is 60° for the machine operation before windingswitching and 180o after winding switching.

Iq1

Id1

I01

⎡⎢⎣

⎤⎥⎦ =

− sin ue( )

cos ue( )

0

cos ue( )

sin ue( )

0

0 0 1

⎡⎢⎣

⎤⎥⎦

a1

b1

I01

⎡⎢⎣

⎤⎥⎦ (15)

Iq2Id2I02

⎡⎣

⎤⎦ =

− sin ue − d( )

cos ue − d( )

0

cos ue − d( )

sin ue − d( )

00 0 1

⎡⎢⎣

⎤⎥⎦

a2

b2

I02

⎡⎣

⎤⎦ (16)

Now these synchronous reference currents Idq01 and Idq02 arecompared with the reference currents Idq01* and Idq02* to generateerror signal for PI controllers. Output of the PI controllers Icdq01and Icdq02 is again transformed back to Iabc and Ixyz using (17) and(18). Subscript ‘c’ is added to the synchronous frame quantities atthis point to distinguish the synchronous frame currents beforeapplying to the PI controller and the output of the PI controller.

IaIbIc

⎡⎣

⎤⎦ =

− sin ue( )

cos ue( )

1

−sin ue − 2p/3( )

cos ue − 2p/3( )

1

−sin ue − 4p/3( )

cos ue − 4p/3( )

1

⎡⎢⎢⎣

⎤⎥⎥⎦

×Icq1Icd1Ic01

⎡⎣

⎤⎦ (17)

IxIyIz

⎡⎢⎣

⎤⎥⎦ =

− sin ue − d( )

cos ue − d( )

1

− sin ue − 2p/3− d( )

cos ue − 2p/3− d( )

1

− sin ue − 4p/3− d( )

cos ue − 4p/3− d( )

1

⎡⎢⎢⎣

⎤⎥⎥⎦

×Icq2Icd2Ic02

⎡⎢⎣

⎤⎥⎦ (18)

These signals are now in three phase sinusoidal form and are fed asreference signals to sin-triangle PWM block to generate the gatingsignals for two PWM inverters.

5 Experimental verification

To validate the field weakening concept using winding switching andthe proposed drive topology, a commercially available SMPMmachine with 24 slots and four poles was arranged and woundaccording to the proposed winding configuration. The experimentalsetup for the proposed machine operation consisted of a DSPcontroller (TMS320F28335 from Texas Instruments) for dataprocessing and control. IGBTs SKM75GB128D from SEMIKRONInternational were used as power switches for the inverters, andthyristors were used for winding switching. A sine triangle PWMwith a carrier frequency of 10 kHz and a maximum modulationindex of 0.8 was used to control the operation of the two inverters.

5.1 Verification of the basic field weakening concept

To verify the basic field weakening concept using windingswitching, the back EMF of the machine was measured for bothmodels before and after winding switching configuration at a ratedspeed of 900 rpm. Additive and subtractive EMFs of the machineusing model-I were measured to be 59.3 Vrms and 34.1 Vrms.The ratio of the experimentally measured additive EMF tosubtractive EMF was 1.739, which validates the analytically

IET Electr. Power Appl., 2016, Vol. 10, Iss. 4, pp. 294–303& The Institution of Engineering and Technology 2016

Fig. 4 Measured back EMF of the machine

a EMF before winding switching for model-Ib EMF after winding switching for model-Ic EMF before winding switching for model-IId EMF after winding switching for model-II

calculated value of 1.73 in (8). Similarly, the additive and subtractiveEMFs of the machine for model-II were measured to be 66.15 Vrms

and 17.65 Vrms. The ratio of additive EMF to subtractive EMF formodel-II provides a value of 3.747, which validates theanalytically calculated value of 3.73 in (9). The measured backEMF waveforms of the two machines are shown in Figs. 4a–d.

5.2 Operation of basic three phase machine

To validate the proposed drive topology, the original three phase machinewas tested to determine the maximum speed range. To preserve themechanical integrity of the machine at maximum speed, a machine

Fig. 5 Steady state currents for the proposed topology before winding switching

a Three phase currents and zero sequence current for winding ABCb Three phase currents and zero sequence current for winding XYZc Current from phase-A and phase-X, andd dq currents of the two inverters

IET Electr. Power Appl., 2016, Vol. 10, Iss. 4, pp. 294–303& The Institution of Engineering and Technology 2016

base speed of 900 rpm was selected. Under these conditions, themachine should achieve a base speed with a rated torque of 7.01 Nmwith a Vdc of 230 V. These operating conditions were taken as therated values of the machine to compare the proposed machine drivesystem operation with that of a conventional three phase machine.

5.3 Operation of the proposed drive topology beforewinding switching

Machine model-I was used for further analysis in this paper becausethe inherent field weakening capability of the machine for model-IIwas predicted to be 3.73 p.u, or 3357 rpm. However, the machine

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Fig. 6 Steady state currents of the machine after winding switching

a Three phase currents and the zero sequence componentb Currents measured at the opposite terminals of phase-AX

under test had very poor field weakening capability using a negatived-axis current and could not go beyond 1200 rpm with the basicthree phase machine control algorithm. Therefore, machinemodel-I was selected to verify the proposed drive topology.

When the machine is operated in a dual three phase configuration,it achieved a speed of 1602 rpm with the rated load for the reasonspreviously explained. However, maximum speed was intentionallylimited to winding switching point speed for this model, that is1.73 p.u or 1557 rpm with a torque of 4.05 N.m. Steady statecurrents of the machine before winding switching are shown inFigs. 5a–d for this mode of operation.

5.4 Operation of the proposed drive topology afterwinding switching

Using a model-I configuration, the windings of the machine wereswitched at a speed of 1557 rpm and a torque of 4.05 Nm. Themachine was then controlled in an open winding configurationwith two CRVIs feeding currents through the machine windings.In this configuration, currents through windings ABC enter at thedotted ends of the machine winding in Fig. 1c, whereas currentleaves at the dotted ends of winding XYZ. Operation continued upto 2700 rpm with a torque of 4.05 Nm in accordance with (11).The power of the machine increased by 1.73 p.u due to theincrease in speed at constant torque of 4.05 Nm. Steady state

Fig. 7 Winding switching transients

a Phase currents and speed torque transient from normal operation to field weakeningb Phase currents and speed torque transient from field weakening to normal operationc Idq transient from normal operation to field weakeningd Idq transient from field weakening to normal operation

300

currents of the machine during operation after winding switchingare shown in Figs. 6a and b.

5.5 Behaviour of the machine during winding switchingtransient

The most critical point of operation in this machine drive system is atthe instant of winding switching when going from normal operationto the field weakening configuration and vice-versa. Successfultransition in both cases is necessary for the continuous operationof the machine. Currents of the winding XYZ are reversed duringwinding switching. Therefore, some current, speed and torquetransients occur during this operation. However, these transientsshould be within limit and should not severely affect thecontinuous operation of the machine. These transients are shownin Figs. 7a–d. A torque transient of about 0.4 Nm and a speedtransient of 20 rpm were observed when switching from normaloperation to the field weakening region and vice versa. It was alsoobserved that, when the machine switched from normal operationto the field weakening region, the speed of the machine decreasedslightly for an instant before the controller brought it back to itsnominal value. Similarly, when the machine switched back tonormal operation from the field weakening region, the flux of themachine was strong and the machine tried to speed up, but thecontroller again brought it back to normal conditions. Moreover,

IET Electr. Power Appl., 2016, Vol. 10, Iss. 4, pp. 294–303& The Institution of Engineering and Technology 2016

Fig. 8 Overall machine operation

a Steady state torquesb Speed torque characteristics of the machinec Power capability of the machine andd Input current

IET Electr. Power Appl., 2016, Vol. 10, Iss. 4, pp. 294–303301& The Institution of Engineering and Technology 2016

Table 2 Overall summary of the machine operation

Machine configuration Back EMF constant Vrms/rpm

Torque,Nm

Torque ripple,%

Pin =m × ei,W

Pout = tω,W

Efficiency(%)

basic three phase 0.0653 7.01 5.25 715.81 660.69 92.30proposed machine before winding switching 0.03788 7.01 3.75 717.94 660.69 92.03proposed machine after winding switching 0.03788 4.05 3.53 723.68 660.35 91.25

the torque of the machine was reduced to 4.05 Nm during windingswitching. This decrease in torque shows that machine currentswere lower due to strong flux during normal operation, whereascurrents were higher after winding switching due to the weak fluxfor the same output torque. However, steady state currents of themachine after winding switching did not go beyond the ratedcurrent limit.

The steady state torque of the machine for the basic three phaseand the proposed topology before and after winding switching aredepicted in Fig. 8a. The speed-torque characteristic curves overthe entire speed range for the basic three phase machine and theproposed topology are given in Fig. 8b. This figure clearlydemonstrates the effectiveness of the proposed topology ascompared with conventional three phase operation of the machine.The basic three phase machine can achieve a maximum of 1200rpm with a maximum negative d-axis current, whereas theproposed drive topology achieved a final speed of 2700 rpmwithout any negative d-axis current. Fig. 8c compares the powercapabilities of the proposed topology and a conventional threephase machine. The machine with the proposed topology canachieve a maximum speed of 1602 rpm before winding switchingwithout any d-axis current. However, to bring the power of themachine to one p.u for smooth winding switching, the power ofthe machine was reduced from 950 W to a rated power of 660 Wover a speed range of 1300 rpm to 1557 rpm by reducing the Iq ofthe machine, as shown in Fig. 8d. After winding switching, themachine was again operated in the constant torque region to a finalspeed of 1.73 times nws according to (11). Therefore, the machinewas operating at 1.73 p.u power (i.e. 1145 W) at a final speed of2700 rpm. If a machine is properly designed to extend its speedrange up to 3.73 times with a negative d-axis current, model-IIwinding configurations can be used to achieve a speed range of1:6.46 using the proposed drive topology. Although the proposeddrive topology requires two half power inverters, it increases themaximum speed capability of a surface mounted PM machinesignificantly. This feature enables a surface mounted PM machineto be used in a traction type application which is normallyconsidered to be poor a candidate for flux weakening operation.Moreover, the proposed topology enhances the maximum powercapability of the machine by extending the constant torque regionof the machine. In addition, the approach does not requirerelatively large values of Xd that is normally required to enhancethe maximum speed limit of the machine using conventional fluxweakening techniques. Such large values of Xd not only increasesthe size of the machine but also negatively impacts the cost, lossesand power factor of the machine.

The overall operation of the machine is summarised in Table 2where Pin is the input power of the machine, m is the number ofphases, e is the back EMF and i is the phase current of themachine. Pout represents mechanical output power of the machine,t represents the torque and ω represents the mechanical angularvelocity of the machine in rad/s.

6 Conclusion

This paper, has presented experimental verification of a windingswitching topology for flux weakening of non-salient PMmachines. A machine model is presented that can achieve twodifferent speed ranges simply by changing the polarity of thewinding coils on the stator of the machine. A drive topology is

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also proposed that enables the machine to operate at a speedbeyond the winding switching point. The salient features of theproposed drive topology include: extension of the constant torqueregion, enhanced output power capability, and successfulswitching from normal operation to the flux weakening region andback again. Experimental results are provided to validate theproposed drive topology.

7 Acknowledgments

This research was jointly supported by the ‘BK21PLUS program’through the National Research Foundation of Korea funded by theMinistry of Education and the ‘Human Resources Program’ inEnergy Technology of the Korea Institute of Energy TechnologyEvaluation and Planning (KETEP), which is funded by theMinistry of Trade, Industry and Energy, Republic of Korea(20154030200730).

8 References

1 Chen, J.J., Chin, K.-P.: ‘Minimum copper loss flux-weakening control of surfacemounted permanent magnet synchronous motors’, IEEE Trans. Power Electron.,2003, 18, (4), pp. 929–936

2 Miti, G.K., Renfrew, A.C., Chalmers, B.J.: ‘Field-weakening regime for brushlessDC motors based on instantaneous power theory’, IEE Proc. Electr. Power Appl.,2001, 148, (3), pp. 265–271

3 Rahman, M.F., Zhong, L., Lim, K.W.: ‘A direct torque-controlled interiorpermanent magnet synchronous motor drive incorporating field weakening’,IEEE Trans. Ind. Appl., 1998, 34, (6), pp. 1246–1253

4 Sudhoff, S.D., Corzine, K.A., Hegner, H.J.: ‘A flux-weakening strategy forcurrent-regulated surface-mounted permanent-magnet machine drives’, IEEETrans. Energy Convers., 1995, 10, (3), pp. 431–437

5 Soong, W.L., Reddy, P.B., El-Refaie, A., et al.: ‘Surface PM machine parameterselection for wide field-weakening applications’. IEEE Industry ApplicationsConf., 2007, pp. 882–889

6 Magnussen, F., Thelin, P., Sadarangani, C.: ‘Performance evaluation of permanentmagnet synchronous machines with concentrated and distributed windingsincluding the effect of field-weakening’. IET Conf. on Power Electronics,Machines and Drives, 2004, vol. 2, pp. 679–685

7 Shakal, A., Liao, Y., Lipo, T.A.: ‘A permanent magnet AC machine structure withtrue field weakening capability’. IEEE Int. Symp. on Industrial Electronics, 1993,pp. 19–24

8 Osama, M., Lipo, T.A.: ‘Modeling and analysis of a wide-speed-range inductionmotor drive based on electronic pole changing’, IEEE Trans. Ind. Appl., 1997,33, (5), pp. 1177–1184

9 Kelly, J.W., Strangas, E.G., Miller, J.M.: ‘Control of a continuously operatedpole-changing induction machine’. IEEE Electric Machines and Drives Conf.,2003, vol. 1, pp. 211–217

10 Jiang, S.Z., Chau, K.T., Chan, C.C.: ‘Included in your digital subscription spectralanalysis of a new six-phase pole-changing induction motor drive for electricvehicles’, IEEE Trans. Ind. Electron., 2003, 50, (1), pp. 123–131

11 Ostovic, V.: ‘Pole-changing permanent-magnet machines’, IEEE Trans. Ind. Appl.,2002, 38, (6), pp. 1493–1499

12 Tapia, J.A., Leonardi, F., Lipo, T.A.: ‘Consequent-pole permanent-magnetmachine with extended field-weakening capability’, IEEE Trans. Ind. Appl.,2003, 39, (6), pp. 1704–1709

13 Huang, H., Chang, L.: ‘Electrical two-speed propulsion by motor windingswitching and its control strategies for electric vehicles’, IEEE Trans. Veh.Technol., 1999, 48, (2), pp. 607–618

14 Zhang, J., Fang, Y., Huang, X., et al.: ‘Design of in-wheel permanent magnetsynchronous motor with concentrated fractional-slot winding and windingswitching technology’. ICEMS, 2013, pp. 1202–1206

15 Nipp, E.: ‘Alternative to field-weakening of surface-mounted permanent-magnetmotors for variable-speed drives’. IEEE Industry Applications Conf., 1995, vol.1, pp. 191–198

16 Hemmati, S., Lipo, T.A.: ‘Field weakening of a surface mounted permanent magnetmotor by winding switching’. 2012 SPEEDAM, 2012, pp. 726–740

IET Electr. Power Appl., 2016, Vol. 10, Iss. 4, pp. 294–303& The Institution of Engineering and Technology 2016

17 Hemmati, S., Lipo, T.A.: ‘Field weakening of a surface-mounted permanentmagnet motor by winding switching’, Electr. Power Compon. Syst., 2013, 41,(13), pp. 1213–1222

18 Tian, B., Zhang, Z., Lipo, T.A., et al.: ‘Investigation of dual-inverter-fed drives forpermanent magnet synchronous motor with winding switching’. Proc. IEEE. Int.Conf. IECON 2014, pp. 709–714

19 Bojoi, R., Levi, E., Farina, F., et al.: ‘Dual three-phase induction motor drive withdigital current control in the stationary reference frame’, IEE Proc. – ElectricPower Appl., 2006, 153, (1), pp. 129–139

20 Senicar, F., Junge, C., Gruber, S., et al.: ‘Zero sequence current elimination fordual-inverter fed machines with open-end windings’. 36th Annual Conf. onIEEE Industrial Electronics Society, 2010, pp. 853–856

21 Bojoi, R., Farina, F., Lazzari, M., et al.: ‘Analysis of the asymmetrical operation ofdual three-phase induction machines’. Electric Machines and Drives Conf., 2003,vol. 1, pp. 429–435

22 Zhao, Y., Lipo, T.A.: ‘Space vector PWM control of dual three-phase inductionmachine using vector space decomposition’, IEEE Trans. Ind. Appl., 1995, 31,(5), pp. 1100–1109

23 Karttunen, J., Kallio, S., Peltoniemi, P., et al.: ‘Decoupled vector control schemefor dual three-phase permanent magnet synchronous machines’, IEEE Trans.Ind. Electron., 2014, 61, (5), pp. 2185–2196

IET Electr. Power Appl., 2016, Vol. 10, Iss. 4, pp. 294–303& The Institution of Engineering and Technology 2016

24 Changpan, Z., Jianyong, S., Guijie, Y., et al.: ‘Four-dimension current vectorcontrol for dual three-phase PMSM’. Electrical Machines and Systems (ICEMS),2014, pp. 1596–1600

25 Said, N.A.M., Fletcher, J.E., Dutta, R., et al.: ‘Analysis of common mode voltageusing carrier-based method for dual-inverter open-end winding’. PowerEngineering Conf. (AUPEC), 2014 Australasian Universities, 2014, pp. 1–6

26 Somasekhar, V.T., Srinivas, S., Gopakumar, K.: ‘A space vector based PWMswitching scheme for the reduction of common-mode voltages for a dualinverter fed open-end winding induction motor drive’. IEEE 36th PowerElectronics Specialists Conf., 2005, pp. 816–821

27 Rama Chandra Sekhar, K., Srinivas, S.: ‘Effect of a CMV elimination PWM onstator current ripple in a dual two-level inverter fed induction motor drive’.SPEEDAM 2012, pp. 395–400

28 Lyra, R.O.C., Lipo, T.A.: ‘Torque density improvement in a six-phase inductionmotor with third harmonic current injection’, IEEE Trans. Ind. Appl., 2002, 38,(5), pp. 1351–1360

29 Holmes, D.G., Lipo, T.A., McGrath, B.P., et al.: ‘Optimized design of stationaryframe three phase AC current regulators’, IEEE Trans. Power Electron., 2009,24, (11), pp. 2417–2426

30 Neubert, M., Koschik, S., De Doncker, R.W.: ‘Performance comparison of inverterand drive configurations with open-end and star-connected windings’. Int. PowerElectronics Conf. (IPEC-Hiroshima 2014 – ECCE-ASIA), 2014, pp. 3145–3152

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