Page - 244 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 616 controlledbybothsides’ inverterbridgesofeachwinding, isaspecificonethatonlyOW-PMSMhas. It is independentbecauseeverywindingdirectlyconnectswith twosides’ inverterbridgesandthere isnodirectconnectionbetweenwindings. Independentmoderequiresbothsides’powersources to supplyvoltageandcanaccomplishenergyflowbetweenpowersources throughwindings. Figure1.StructureofOW-PMSMdrivesystem. 2.1.WindingModeFeaturesAnalysis First,wewilldiscusspowersource limitationsonwindingmodes. Indifferentwindingmodes, themaximumamplitudeof eachwinding’sphasevoltage isdifferent and theconnectionbetween eachphase isdifferent too,which leads to adifference inbasic voltagevectors’ amplitude. When thewindingmodeisstaror independent,acertainphasevoltagecannotbedeterminedaccordingto the corresponding inverter bridge’s switching status andwill be influenced by inverter bridges’ switching status of other phases due to the load neutral point in star mode and themid-point potentialdifference in independentmodefloating. For instance, instarmode,wheninverterswitch statusesare (110) (phaseAandBupperbridgearmon,phaseClowerbridgearmon),phasevoltage relations:uA=uB=Vdc/3,uC=−2Vdc/3;whenswitchstatusesare (100),phasevoltagerelations: uA = 2Vdc/3, uB=uC=−Vdc/3. It can be seen that, althoughphaseA’s corresponding inverter bridge’sswitchstatusesare thesameinbothsituations,owingto the loadneutralpoint’sfluctuation in starmode, phase voltages uA in both situations are different. Using the schematic diagramof mid-pointvoltage inFigure2,wecananalyzevoltagevectors.Wefirstequallydividepowersource 1andpowersource2 into twopartsaccording tovoltage todeterminevirtualmid-pointsmandn. Thevoltagedifferencebetweeneach inverterbridge’soutputandthecorrespondingmid-point is the mid-pointvoltageandisunaffectedbyfloatingneutralpotentialormid-pointvoltagedifference. Each inverterbridge’s switchingstatusandmid-pointvoltagehasaone-to-onecorrespondence. Theresults are identicalwhenusingmid-pointvoltageandphasevoltage forvoltagevectorsynthesis. Starandtrianglemodesarepoweredviaasinglepowersourceandthemotor’s three-phasestator windingsareconnected inaspecific topologystructure. Switchingstatusesof three-phase inverter bridgescanformavoltagevector in themotorspaceplane.GiventhatDCbusvoltage isVdc,when switching statuses are (110), synthesizingvoltage vector in star and trianglemodes are shown in Figure 3a,b. Independentmode ispoweredbydual sources. Supposed that thevoltageofpower source1 isVdc1 andthevoltageofpowersource2 isVdc2,whenleft switchstatusesare (110)andright switchstatusesare (001),voltagevectorsynthesis in independentmodeisshowninFigure3c. 244