Page - 243 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 616 Control strategiesofOW-PMSManddual invertershavealwaysbeenaresearchfocus.Winding topologyandconfigurationsarewidelydiscussed inorder tooptimize themotor’sworkingrange and efficiency [17–19]. Fault-tolerant operation [20–22] and zero-sequence voltage elimination method [23,24] are alsounder extensive research. Loncarski, J. et al. compared theoutput current rippleinsingleanddual invertermotordrivesforelectricvehicles,concludingthatthedual-2Linverter canactasa3L inverterandoffersasignificant ripple reduction[2],whichcanalsobeobserved in this paper.AnQun-tao,SunLietal. proposedadual invertersSVPWMmodulationmethodforcurrent controlandin thiswayvoltagevectorsynthesized in therangeofahexagonandwhenthebusvoltage remainsconstant, thebasespeedof theelectricmotorcouldbe1.7 times that inY-connectionwithout generatingzero-sequencevoltage [7,8]. ZhanH.,HengN. et al. studieda commonDCbus-based dual invertersSVPWMmodulationstrategy. In thisway, theamplitudeof thevoltagevectorcould bemaximizedandat thesametimeazero-sequencecurrent couldbesuppressed [23,24].Welchko studieddualsources-baseddual inverters’voltagevectorsdistribution,andproposedthree typesof voltagedistributionmethodstoadapt todifferentworkingconditionsofhybridvehicles toachieve energymanagement functionsbetween twopower sources [16]. However, the two inverterswork independentlywithoutcoordination,andthustheswitchingfrequencyof inverterdeviceshasalso doubled,which increases the inverterswitching loss.All thestudiesdiscussedabovehaveproposed currentcontrolmethodsofdual invertersbutdivisionofOW-PMSMwindingmodesandwinding modesswitchingarenot involved.NguyenN.K.etal. studieddual inverters-five-phaseOW-PMSM’s windingmodes,dividedintothreetypes,starmode,pentagonmode,andpentaclemode,andanalyzed theexternalmotorcharacteristicsofeachmode[18].However, thewindingmodesareonlydecided basedonrotational speed.Adetailedwindingmodesswitchingmethodhasnotbeenproposed,nor has there been an analysis of the energydistribution issue betweendual sources. Therefore, it is necessarytoproposeacontrolmethodthatcouldmanageenergydistributionsbetweenpowersources, andmakefulluseofeachwindingmode’sworkingrangetoreduce inverter lossandincreasesystem efficiencyforelectricvehicles. Thispaperfirstanalyzes the three-phaseOW-PMSMwindingmodesdivisionmethodandthe externalmotorcharacteristicsofeachwindingmode.Onthatbasis,weproposea torquesaturation windingmodesswitchingstrategy,which is insensitive tomotorparameters, toaccomplishautomatic windingmodes switching according todifferentworking conditions. Then, amulti-level current hysteresismodulationalgorithmused in independentmode isput forward. This algorithmcould set themajorpowersourceandachievereal-timemajorpowersourceswitchingtodistributeenergy betweentwopowersources. Inaddition,wedesigntwocontrolmethods: a lowswitchingfrequency methodandahighpowerdifferencemethodfordifferentenergydistributionpurposes.At theend of this paper, the feasibility and effectiveness of theproposedwindingmodes switching strategy andmulti-level current hysteresismodulation are verified through simulations. Vehicle economy performancesimulationalsoshowedthat theelectricvehicleunder theproposedcontrolmethodhas betterefficiency. Inparticular, coordinationtransformationsbetweenthe three-phasestatorandtwo-phaserotator in thispaperwereequivalentpowerconversions. 2.WindingModeFeaturesAnalysisandSwitchingStrategy ThedualsourcesOW-PMSMdrivesystemstructure is showninFigure1. Accordingtodifferentwindingconnections, three-phaseOW-PMSMcanbedividedinto three types: starmode, trianglemode, and independentmode. Starmode’swinding connection copies traditionalPMSMs. It requiresheadsor tailsof three-phasestatorwindingsconnectedatonepoint. If it isadual invertersconfiguration, it couldbecompletedbymakingeachbridge’s lowerarmturned onsimultaneously in the idle inverter. Trianglemodeisaccomplishedthroughconnectingtheheads andtailsof three-phasestatorwindings inacircle. Indual invertersconfiguration, it couldbeachieved by shuttingdownonepower source and turningona triangle circuit switch. Independentmode, 243