Page - 31 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 1217 Figure36. Inductionmotordrivecharacteristics.Maximumtorque ismaintainedtillbasespeed,and thendecreasesexponentially.Adaptedfrom[4]. 5.5. SwitchedReluctanceMotor (SRM) SRMs,alsoknownasdoublysalientmotor (becauseofhavingsalientpolesboth in thestatorand therotor)aresynchronousmotorsdrivenbyunipolar inverter-generatedcurrent. Theydemonstrate simpleandrobustmechanical construction, lowcost, high-speed, less chanceofhazards, inherent longconstantpowerrangeandhighpowerdensityuseful forEVapplications. PMisnot requiredfor suchmotorsandthat facilitatesenhancedreliabilityalongwith fault tolerance.Onthedownside, they areverynoisybecauseof thevariable torquenature,have lowefficiency,andare larger insizeand weightwhencompared toPMmachines. Thoughsuchmachineshaveasimpleconstruction, their designandcontrolarenoteasyresultingfromfringeeffectofslotsandpolesandhighsaturationof thepole-tips [4,23,30,70]. Becauseofsuchdrawbacks, thesemachinesdidnotadvanceasmuchas the PMor inductionmachines.However,becauseof thehighcost rare-rareearthmaterialsneededinPM machines, interest inSRMsare increasing.AdvancedSRMslike theonedemonstratedbyNidec in 2012hadalmost interiorpermanentmachine (IPM)-likeperformance,witha lowcost. Reducingthe noiseand torquerippleare themainconcerns in researchesassociatedwithSRMs[23]. Oneof the configurations thatcameoutof theseresearchesusesadual statorsystem,whichprovides lowinertia andnoise, superior torquedensityandincreasedspeed-rangecomparedtoconventionalSRMs[77,78]. Designbyfiniteelementanalysiscanbeemployedtoreducethetotal loss [79], controlbyfuzzysliding modecanalsobeemployedtoreducecontrol chatteringandmotornonlinearitymanagement [80]. 5.6. SynchronousReluctanceMotor (SynRM) ASynchronousReluctanceMotorrunsatasynchronousspeedwhilecombiningtheadvantagesof bothPMandinductionmotors. Theyarerobustandfault tolerant likeanIM,efficientandsmall likea PMmotor,anddonothave thedrawbacksofPMsystems. Theyhaveacontrol strategysimilar to that ofPMmotors. TheproblemswithSynRMcanbepointedas theonesassociatedwithcontrollability, manufacturingand lowpower factorwhichhinder itsuse inEVs. However, researcheshavebeen goingonandsomeprogress ismadeaswell, themainareaof concernbeing therotordesign. One wayto improvethismotor isby increasingthesaliencywhichprovidesahigherpower factor. It can beachievedbyaxiallyor transversally laminatedrotorstructures, suchanarrangement isshownin Figure 37. Improveddesign techniques, control systemsandadvancedmanufacturing canhelp it make itswayintoEVapplications [23]. 31