Page - 30 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 1217 motorscanalsobeconstructedusingacombinationofreluctancemotorandPMmotor.Controlling theconductionangleof thepowerconvertercan improve theefficiencyofPMBLDCsaswellasspeed range, reachingashighas four times thebasespeed, thoughtheefficiencymaydecreaseatveryhigh speedresultingfromdemagnetizationofPM[4].Other thanthePMhybridconfigurations,PMBLDCs canbeburiedmagnetmounted—which canprovidemore air gapfluxdensity, or surfacemagnet mounted—whichrequire lessamountofmagnet. BLDCsareuseful foruse insmall cars requiringa maximum60kWofpower [72]. ThecharacteristicsofPMBLDCsareshowninFigure35. Figure35.CharacteristicsofaPermanentMagnetBrushlessDCMotor. The torqueremainsconstantat themaximumright fromthestart,butstarts todecreaseexponentially forspeedsover thebasespeed. 5.3. PermanentMagnetSynchronousMotor (PMSM) Thesemachinesareoneof themostadvancedones,capableofbeingoperatedatarangeofspeeds withouttheneedofanygearsystem.This featuremakesthesemotorsmoreefficientandcompact. This configuration isalsoverysuitable for in-wheelapplications,as it is capableofprovidinghightorque, evenatvery lowspeeds. PMSMswithanouter rotorarealsopossible toconstructwithout theneedof bearings for therotor. But thesemachines’onlynotabledisadvantagealsocomes induring in-wheel operationswhereahuge iron loss is facedathighspeeds,makingthesystemunstable [73].NdFeB PMsareusedforPMSMsforhighenergydensity. Thefluxlinkages in theair-gaparesinusoidal in nature; therefore, thesemotorsarecontrollablebysinusoidalvoltagesuppliesandvectorcontrol [70]. PMSMisthemostusedmotor intheBEVsavailablecurrently;at least26vehiclemodelsusethismotor technology[5]. 5.4. InductionMotor (IM) InductionmotorsareusedinearlyEVs like theGMEV1[23]aswellascurrentmodels like the Teslas [54,74]. Among thedifferent commutatorlessmotordrive systems, this is themostmature one[2]. Vectorcontrol isuseful tomakeIMdrivescapableofmeeting theneedsofEVsystems. Sucha systemwiththeability tominimize lossatanyloadconditionisdemonstratedin[75]. Fieldorientation control canmakean IMact likea separately excitedDCmotorbydecoupling itsfield control and torquecontrol. Fluxweakeningcanextend thespeedrangeover thebasespeedwhilekeeping the powerconstant [30],fieldorientationcontrol canachievearange three tofive times thebasespeed withanIMthat isproperlydesigned[76]. Threephase, fourpoleACmotorswithcopperrotorsare seentobeemployedincurrentEVs.Characteristicsof IMareshowninFigure36. 30