SOCIETYAUTOMOTIVE ENGINEERS, INC. 400 Commonwealth DriveWarrendalePa.15096 DesignandApplication ofTractionMotorsfor ElectricVehicles P.K.LindhorstandJ.C.Andreas CenturyElectricDiv.,GouldInc. NationalCombinedFarm,Construction &Industrial MachineryandPowerplant Meetings Milwaukee. Wis. September 9-12,1974740729 New Text New Text New Text New TextNew Text New TextDownloaded from SAE International by Purdue University, Sunday, August 19, 2018New TextDownloaded from SAE International by Purdue University, Sunday, August 19, 2018740729 DesignandApplication ofTractionMotorsfor ElectricVehicles P.K.Lindhorst andJ.C.Andreas CenturyElectricDiv.,GouldInc. WHYCHOOSE AD-CMOTOR Directcurrent(d-c)motorsystemsarepredominately used forelectricvehicleapplications duetotheircharacteristics andrelativesystemscostwhencomparedtoa-cmotorsystems. Thea-csystememploysarelativelysimpleinductionmachine inconjunction witharathercomplexpolyphasecontrol.The controlisgenerallyoftheinvertertype,variablevoltage,and frequency. Incomparison, thed-csystemutilizesamorecom plexmachinehavingslidingcontactstothearmaturecircuit viaacommutator andbrushes.Thebrusheswearandmustbe replacedperiodically. Thecontrolisnormallyasimplevari ablevoltaged-ccontrolutilizingresistorsorsolid-statechop per-typecircuitry.Whileadjustablespeeda-cdrivesarecur rentlyavailable,theyareemployedonlyinasmallpercentage ofadjustablespeedapplications primarilyduetohighercosts. DCMOTORCHARACTERISTICS SPEEDVERSUSTORQUE -Theshapeofthespeed-torque curvecanbevariedtopracticallyanyformwithincertain limits,includingoperationinallfourquadrants(bothrota tions,motoring,orregenerating (Fig.1)).Thisisaccomplished throughtheselectionoftheexcitationtypeandthecontrolof themotorpowersupply. CONTROL -Theseadjustments inthespeed-torque curveareaccomplished bycontrollingtheinputvoltagetothefield orarmatureorboth.Otherpossibilities areprecisespeedreg ulationwithtachometer feedback,limitingmaximumtorque andcurrent,controlofacceleration anddeceleration, etc. BRAKING -Byoperatingthemotorasagenerator,through theuseofacontrol,regenerative brakingcanbeaccomplished quiteeasily.Bycontrollingtheexcitationoftheseparately excitedtypemachine,thegeneratedvoltagecanberaised abovethatofthebattery,andsomeofthekineticenergycan betransferredbackintothebattery.Thisnotonlycanreduce thesizeofmechanical brakerequired,butalsoconservesen ergy.Anothermethod,knownasdynamicbraking,discharges thepowergeneratedintoaresistorandcausesbrakingofthe motor.Inaddition,themotorcanbeelectricallyreversedand energized,creatinganegativetorque.Thesemethodsmustbe appliedcautiouslyassevereheatingofthemotorcanoccur. REVERSING -Again,bypropercontrol,rotationcanbe smoothlyreversedwithoutpowercircuitswitching. EFFICIENCY -Particularly inapplications requiringawide speedrangeandfrequentstopsandstarts,d-csystemsare generallymoreefficientthanothertypes. TYPESOFEXCITATION SHUNTWOUND-Withthefieldwindingconnecteddirectly acrossthearmature,characteristics aresimilartothecurve ABSTRACT Thedesignofelectrictractionmotorsforelectricvehicle applications requiresintimateknowledgeofthevehiclemis sionandperformance requirements andasystemsapproach involvingintegrationofthemotorintotheentireelectricalpowersystem.Motorcharacteristics arereviewed,speedcon trolpossibilities arediscussed,andfactorstobeconsideredin theapplication andselectionoftractionmotorsareexplained indetail. Downloaded from SAE International by Purdue University, Sunday, August 19, 20182 drawninFig.2A.Thistypeismostoftenusedwherecon stantspeedatanycontrolsettingisrequiredregardlessofload variationsandwhereanappreciable speedrangeisdesiredby fieldcontrol. Insomeshuntmachines,thespeedriseswithincreasedload, particularly atweakfieldsettings.Inthiscase,aweakseries windingcanbeaddedtostabilizethemachineandthema chineiscalledshunt-stabilized. Theadditionofthiswinding createsamorecomplicated controlifreversingisrequired.In somecases,however,thereversecharacteristic maynothave thesamerequirement astheforward,andthestabil