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Electric traction machine choicesfor hybrid & electric vehiclesPresented for:byJames R. HendershotNov 20, 2014hendershot@ieee.org941 266 7631Edited by. Prof. Dr. Ernie FreemanJR Hendershot 20141

Early electric cars in USAAllison driving earlyFord-Edison carEdison’s 1896electric quadricycle100 miles percharge!!!1913 Edisonelectric carJames Hendershot 20142

As we approach 2015 there are a bunch of Hybrids or plug-insbeing produced around the world with many more to comePorsche SE-HYBRIDMercedes-Benz B-Class Electric DriveVW JETTASonata HybridBMW i3Nissan LeafJames Hendershot 20143

Largerair-gapSmallerair-gapTwo most popularvehicle tractionmotor choicesBrushlessstator designtypical of anAC InductionmachineJames Hendershot 20144

Abstract:“Electric traction machine choices for hybrid & electric vehicles”How and why did the design engineers decide which electric machine type todevelop for modern hybrid & pure electric vehicles? Similar machine typesseem to be used in all hybrids. The all electric vehicles have been developedusing a different machine topology. This presentation reviews the Toyota PriusHybrid vehicle and many that followed to gain insight to this question.It is the author’s desire the engineers interested in vehicle traction motor designand selection will come away with a clear understanding of the choices, sometradeoffs and a starting place in mind for their own efforts.Many photographs and details are presented for the drive train of nearly everysuch vehicle currently in production. Knowledge of what has been done beforemakes sure that re-invention is avoided.“In order to be a creator of progress It is better to stand on the shoulders ofthose before you to enable you to see over their heads into the future”Paraphrased from Isaac Newton”JR Hendershot 20145

17 years have now passed now since Toyota came out with the first Prius(One year after the GM EV-1)General Motors came out with the first production electric vehicle in 1996Going back further, Thomas Edison came out with an electric car in 1895Interesting results since 1996 (date of first Prius)Only production car using an AC Induction motor for traction is the TESLAGM Volt rumored to use both an IPM and and AC induction motor for VOLTAll other hybrids and electric cars in production use IPMsSo my advice to you all is “don’t re-invent any old motor concepts but onlyuseful modifications of them or better still, new designs. Therefore we musthave a quick look at the current electric cars and/or their electric motors to seewhat has already been done to make sure you drive on the right road !!JR Hendershot 20146

Toyota Prius(3,166,000 sold from1997 through mid 2013)1997Rated 33 kW @ 4500 rpmMax motor speed 5600 rpmBattery voltage 288 VDCDC to DC boost to 500 VDCPeak torque 350 Nm2003Rated 50 kW @ 1200 to 1540 rpm33 kW 1040 to 6,000 rpm max.Battery voltage 201.6 VDCDC to DC boost to 500 VDCPeak torque rating 400 NmJR Hendershot 20142009Rated 60 kW @ ? rpmMax motor speed 13,500 rpmBattery voltage 201.6 VDCDC to DC boost to 650 VDCPeak torque rating 207 Nm7

Comparison of Toyota, 2010 Prius, LS600 Lexus, Camry and 2004 Priuscopyright, 2014, J R Hendershot8

Toyota has used such FEA simulation techniques to constantly improvetheir IPM designs for their Hybrid cars. Some examples shown below:Toyota 2010PriusJR Hendershot 2014new webretention9

1996 GM EV-1Traction motor3 phase AC Induction, aluminum rotorMotor speed0 to 7000 rpmRated output power102 kW (137 hp)Torque from 0 to 7 krpm 149 Nm (110 lbf-ftFixed gear ratio with no transmissionOriginal batteries “Deep cycle lead acid”, 312 VDC, 100 mile rangeDelco-Remy “NiMH batteries”, 343 VDC, 160 mile rangeAcceleration 0 to 60 mph 8 sec (Max speed 80 mph)JR Hendershot 201410

Toyota rotor & stator lamination cross section evolution1997 Rotor2003 RotorJR Hendershot 2014Notice the magnet designchanges & center retentionwebs in 2007 Camry, 2008Lexus & 2009 Prius.(Very good design reasons)11

Lets have a peek at some of these unique motor designsFord EscapeChevy VOLTNote:It appears that many automobilemanufactures have elected todesign their motors and drives inhouse rather than working withexisting electric motor companies.BMW i3JR Hendershot 201412

Ford electric traction motor details (Escape, Focus or Fusion?)8 pole rotor16 magnetsFord Focus 123 HP (92 kw)(8) Pole IPM RotorCopper end ringsor balance rings?JR Hendershot 2014Hi slot fill (70%)13

GM VOLT originally usedthe REMY 10 poledouble layered IPMmotor with a hairpinwound statorvoltage 700Output torque 170 NmOutput power 150 kWMax speed 10,000 rpmThere is also an aluminum rotor ACInduction motor used in the VoltWork continues by REMY & GM toconvert its rotor to a copper rotorJR Hendershot 201414

Chevy VOLT electric traction motor detailsFINISHEDSTATOR10 pole IPMRotor &Stator40 magnetsHair-Pin windingsHi slot fill using square wireJR Hendershot 201415

According to both REMY & GM, the 60 slot statorwith hair-pin windings can be used with either theIPM or the Caged rotorLoadedfield plotPM Pole DesignOptimizationPhase AJR Hendershot 201416

BMW i3 electric traction motor details (Landshut Germany)Motors/Drivespackaged for testPhase coilinsertion12 pole IPM rotorMagnet InserterEnd turn lacingStacking (5) rotor segmentsShed winderfor phase coilsBMW patent application Nº 2012/0267977Phase terminationJR Hendershot 2014Phase termination17

Quick view of various motors intended for vehicle tractionZEMOTERINGAVL HybridDriveHyundaiSonataEBusMercedes-Benz PU106A(15,000 rpm)YASAZYTEK 170 kwPorscheLEXUS2009 PorscheSUMOCayenneJR Hendershot 201418

Two SPM traction motorsMotors by Danaher(Pacific Scientific)JR Hendershot 201419

New people movers with one or two wheels 1200EN-VbyGeneralMotorsHonda U3-XRYNOMOTORSUNOJR Hendershot 201420

Increasing the number of poles (all machines)Increasing the number of poles decreases the motor OD and mass(assuming rotor O.D. does not change)Prof. W. L. Soong, U of AdelaidaJR Hendershot 201421

Optimum pole number for AC inverter driven machines014140140014000(Nm)Optimal pole numbers for AC inverter driven motorsFor most all traction motors the optimum number of poles 4 resulting in lowestleakage reactance, highest power factor and efficiencyIPMs do not have this limitation so all IPM traction motors are 8, 10 or 12 polesIPMs should be smaller and lower in mass than AC inductance machinesJR Hendershot 201422

The Tesla traction motor is a 4 Pole design.The IPM – AC brushless machines are synchronous motors with high polesThe Switched reluctance motor is a synchronous machine with high polesThe Reluctance Synchronous motor is sort of in between, although it is asynchronous machine the pole number can be 4, 6 or 8 for traction.Each machine has their pros and cons which we will not discuss here.Suffice to say that all types of motors with no magnets are on the tableJR Hendershot 201423

Same stator with three rotor choicescopyright, 2014, J R Hendershot24

Three rotor configurations usingsimilar stators and windings.All three machines areInverter fed for mostspecific requirementsIMRSMRPM sensorAnglesensorIPM or SPMSRMAnglesensorSR machines require, new stators& windings plus new half-bridgeinverter/control technologyJR Hendershot 2014Anglesensor25

A comparative graphic of electric machine choices for vehicletraction & accessory motors (Besides brushed PM DC)** NO RARE EARTHMAGNETS NEEDED** AC INDUCTIONPM-AC SYNCHRONOUS* *SWITCHED RELUCTANCE** RELUCTANCE SYNCHRONOUSJames Hendershot 201426

Easy automated AChigh slot fill statorHair-pin stator automatedwinding with high slot fill.(Can be round or rectangular)Applicable to all three machinetypes except SRJR Hendershot 201427

Doubly salient pole reluctance machines called Switched Reluctance (SRM)(Some have called the SRM, “the good, bad & ugly”!!)GOOD !The SRM is one of the oldest electric machines dating back to the middle19th century but not practical until the development of the transistor.Very simple in construction and low cost to manufactureSRMs are very robust and reliable with decent fault toleranceBAD !Tricky to control & requires custom half bridge power switching circuitsRequires double number of connections as other machinesRequires double the number of power switching devices of other machinesUgly !Tends to be noisy without special attention to designRequires careful commutation to minimize torque rippleJR Hendershot 201428

Examples of 3, 4 & 5 phase SR machine cross -phase12-85-phase10-6JR Hendershot 201429

Photos of 200 KW SR motor design by Dr. Sergie Kolomeitsevfor direct drive pump application, prototyped by a US company.Air-GapdetailsSR Motormountedon pump(3) phase 12-8 SRStator OD 770Rotor OD 467Stator coil detailsJR Hendershot 2014(8) tooth rotor30

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John Deere 944 hybrid Loader (5900 liter capacity) with (4) SR traction motors270 HP Switched Reluctance130 HP Switched ReluctanceJR Hendershot 201432

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Hi performance Switched Reluctance IC engine generatorPAT # US 7755308JR Hendershot 201434

Water Cooled SR traction drive tested by VOLVOPUNCHJR Hendershot 201435

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AC Induction machine is most elegant motor of all, Rotating TransformerJR Hendershot 201437

AC Induction motors for vehicle tractionTesla Sport4 Pole AC InductionmotorsTesla SedanJames Hendershot 201438

Some details regarding the AC Induction motor used by TESLASportSportSportSedanJames Hendershot 201439

Tesla electrics using AC Induction traction motors48 slots68 barsRated output power 288 HPPeak Torque 300 lbf-ft(0 to 5000 rpm)Max speed 14,000 rpmTesla Model STraction MotorCopper RotorJR Hendershot 201440

AC PropulsionWrightSpeed0 to 60 mph, 2.9 secAC Propulsion motor6000 laptop batteriesJR Hendershot 201441

Powerful AC Induction motor used for Rail traction drives4-POLEAsynchronous rotor-statorintended replacementTypical open frame air cooled machineDesigned by JR Hendershot forJR Hendershot 201442

Reluctance motors and generators types,RSM, single salient pole & SRM dual salient poleRSMRSM (Reluctance-Synchronous) usesstandard Induction stator and specialsalient pole rotor configurationsSRMRSM (synchronous-Reluctance) typeshave salient poles in both rotor andstator at air gap like gear teeth. Phasecoils are normally placed around eachstator tooth.JR Hendershot 201443

Attractiveness of RSM for tram, Rail, car and truck tractionLow cost investment to change from Asynchronous machine with slip toa Synchronous machine with zero slipUse same frames, shafts, bearings and cooling systemUse same stators for induction machines (maybe change turns?)Use same inverters with slight change in softwareUnknown issues to ponder?New design only of simple salient rotor seems the only major task?Can a motor made up of flux barriers and flux carriers be designedwith sufficient mechanical integrity for rail duty?Can the rotor saliency ratio be high enough to match of exceed thetorque density and power factor of the Asynchronous machine?JR Hendershot 201444

Well recognized power bridge circuit for ACInduction, Reluctance Synchronous andBrushless DC, PM-Asynchronous drives.Typical power bridgefor all Block or Sinecommutation methodsJames Hendershot 201445

Another reluctance machine made from completely different components3-phase, 6-4Stator core from stampedelectrical steel laminationsRotor core from stampedelectrical steel laminationsLayer wound coils fittedaround each stator toothVery robust and low costcost machine with high faulttolerance(No magnets required!)James Hendershot 201446

Half Bridge power circuit required for switched reluctance drivesEach load connects toa stator phase withtwo connectionsAll phases are inparallel between theDC rails and arecontrolled separatelyPrecise phase firingangles are required forefficient operationAt high speeds theuse of continuouscurrent conductionis very useful.Three phase circuit shown, add a dual transistor half bridge for each additional phaseJames Hendershot 201447