Chapter30_Drive and Control System for Hybrid Electric Vehicles

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DK3023_book.fmPage657Friday,April8,20059:34AM30DriveandControlSystemforHybridElectricVehiclesWengKeongKevinLim,SamanKumaraHalgamuge,andHarryCharlesWatsonUniversityofMelbourne,Melbourne,Australia30.1INTRODUCTIONHybridvehicleshavemultiplepowersourcesthatcanbeseparatelyorsimultaneouslyusedtopropelthevehicle.Differentwaysofintegratingthesepower-producingcompo-nentswithelectricalenergystoragecomponentsallowfordistincttypesofhybridelectricvehicle(HEV)configurations.Generally,fuelenergymaybeconvertedbyanumberofdistinctheatengines,suchasaninternalcombustionengine(ICE),whileanelectricalmotor(EM)derivesitselectricalenergyfrombatteries,ultracapacitors,solarcells,fuelcells,orgeneratorsdrivenbyheatenginesorflywheels.Todate,themostpromisinghybridvehicleistheHEVdrivenbyanICEandanEMpoweredbyon-boardbatteries.HEVsolvesmanypureelectricvehicles’problemsandminimizestheshortcomingsofconven-tionalvehicles,whileprovidingthebenefitsofbothelectricandconventionalvehicles.Themajorhybridconfigurations(HCs)areseriesandparallelconfigurations,showninFigure30.1andFigure30.2,respectively.Inserieshybrids,anICEpowersageneratorthateithersupplieselectricalpowertotheEMorchargesthebatteries.TheICEdoesnotmechanicallydrivethewheelsdirectly.Asfortheparallelhybrid,anICEsuppliesmechan-icalpowerdirectlytodrivethewheels,withtheEMdirectlycoupledtothepropulsionsystem.ParallelhybridshavetheflexibilitytopropelavehiclewithpureICEonly,pureEMonly,oracombinationofbothICEandEMsimultaneously,basedontheControlStrategy(CS)settings.Currentlythereexistsathirdtypeofhybridconfigurationthatcombinesthebestaspectsofbothseriesandparallelconfigurations,knownastheseries-parallelhybrid,asshowninFigure30.3.ThisconfigurationallowstheICEtodirectlydrivethewheels,butalsohastheabilitytosimultaneouslychargethebatteriesandtopowertheEMthroughagenerator.©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage658Friday,April8,20059:34AMInternalCombustionGeneratorEngineMotorWheelsBatteryMechanicalLinkElectricalLinkNote:ArrowindicatespowerflowdirectionFigure30.1Serieshybridconfiguration.InternalCombustionClutchEngineTorqueWheelsCoupler&TransmissionBatteryMotorMechanicalLinkElectricalLinkNote:ArrowindicatespowerflowdirectionFigure30.2Parallelhybridconfiguration.InternalCombustionWheelsEngineBatteryGeneratorMotorMechanicalLinkElectricalLinkNote:ArrowindicatespowerflowdirectionFigure30.3Series-parallelhybridconfiguration.©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage659Friday,April8,20059:34AMBesidesHC,HEValsomakesadistinctionbetweenchargedepletinghybridsandchargesustaininghybrids.Chargedepletinghybridsallowtheirbatteriestobedepletedanddonothavetheabilitytorechargethematthesamerateastheyarebeingdischarged.Thistypeofhybridgivesmoreprioritytopropellingthevehicleunderpureelectricmodemostofthetimeanddepletesitsbatterystateofcharge(SOC)toitsminimumlevelwithintheallowableSOCoperatingrange.WhentheSOCreachestheminimumlevel,theICEwillbetriggeredtodrivethegeneratortorechargethebatterybacktoitsmaximumSOC.WhentheSOCishigh,theICEisshutoffandthevehicleisdrivenunderpureelectricmodeuntiltheSOCdepletestoitsminimumlevelagain.Inchargesustaininghybrids,theICEisadequatelysizedtomeettheaveragepowerload,andwheneveroperatedundertheexpectedconditions,itwillbeabletomaintainadequatereserveofenergyinthebatteriesatalltimes.Duringhigh-powerdemandthebatteryprovidesthepeakpower,whileinlow-powerperiodsthebatteryisrechargedsuchthattheSOCalwaysmaintainsaroundthemid-leveloftheallowableSOCoperatingrange.WhenevertheSOCishighabovethemid-level,moreelectricalpowerwillbeusedtodrivethevehicle,thusreducingfuelconsumptionandemission.IftheSOCisfarbelowthemid-level,ICEwillbeusedtodrivethegeneratortoquicklyrechargetheSOCbacktoitsmid-level.WhenmultiplepowersourcesareusedtodriveanHEV,aneffectivepowerman-agementandcontrolalgorithmisessentialtocontroltheflowofenergyaswellastomaintainasufficientreserveofenergyinthestoragedevices.Theexistenceofapowermanagementandcontrolalgorithm,whichisbetterknownasaControlStrategy,ensuresthatallpowercomponentsoperatetogetheratoptimalefficiencytoachievemultipledesignobjectiveslikemaximizedfueleconomyandminimizedemission.BoththeHCandControlStrategymustbedesignedtogethertoachievetheseobjectives.AlthoughHCmightdeterminetosomeextentwhattypeofCSshouldbeimplementedforaspecificHEV,thereisstillawiderangeofCSforeachHC.TheseCSsmanagetheenergyflowbetweenallhybriddrivetraincomponentsandoptimizepowergenerationaswellaspowerconver-sioninindividualcomponents.SelectingthemostsuitableCSwillhaveasignificantimpactonfueleconomy,vehicleperformance,andemissions.30.2CONTROLSTRATEGYThemainobjectiveofahybridelectricvehicleistomaximizefueleconomywhileminimizingemissions.Toachievetheseobjectives,theHEVmustbecarefullydesignedwithapropercombinationofhybridhardwareconfigurationandawell-developedpowermanagementalgorithm.ThesepowermanagementalgorithmsarebetterknownasControlStrategiesthathandletheproperflowofpowerandmaintainadequateamountsofreserveenergywithintheon-boardbatterypacks.Ingeneral,theinternalcombustionengineofanHEVisoftenundersized,andtheCSwillensurethatitalwaysoperatesnearoratitsmostefficientpoint.Toovercomethevehicle’srequirementduringtransients,anelectricmotorisadoptedtoprovidetheadditionalpeakpowertoassisttheICEwhenevernecessary.Therefore,theroleoftheCSistodeterminewhenandhowmuchenergyshouldbedrawnfromeachpowersourcetopropelthevehiclewhileachievingtheobjectivesoftheHEV.Duringdecelerationorbraking,theCSwillalsoactivatetheregenerativebrakingmode.Thespinningdrivelineisdisengagedfromthedrivingpowersourcesandusedtodriveeitheranon-boardgeneratororanEMasagenerator,toproduceelectricalenergyforrechargingthebatteries.Theexternalfrictionforceandthegeneratorloadwillslowdownthedrivelineand,hence,thevehicle;thisisknownasdrivelinebraking.The©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage660Friday,April8,20059:34AMremainingbrakingpowerwillbesuppliedbytheconventionalbrakepadsactingondiscordrumtobringthevehicletoastopatthedesiredpace.Inthiswaysomebrakeenergycanberecoveredtoimprovetheoverallenergyefficiencyofthevehicle.Ifthebrakingisabruptthenlessbrakeenergywillberecovered,asthefrictionbrakingwillbehandlingmorebrakingjobsthanthedrivelinebrakingtostopthevehicleinstantly.Hence,regen-erativebrakingwillrecovermorebrakepowerwheneverthevehicleisgraduallydeceler-atedandbroughttoastop.ThefollowingwilldiscusssomecommonControlStrategiesthatareadoptedbymostHEVs.30.2.1THERMOSTATSERIESCONTROLSTRATEGYTheSeriesThermostatCSisaserieshybridconfigurationCSthatusestheICEalongwithageneratortopowertheEMtopropelthevehicleandrechargethedepletedbatteries.Thebatterystateofchargeisallowedtofluctuatebetweenthemaximumandminimumsetpoints,ratherlikeathermostatthatmaintainsthetemperaturewithinthedesiredrange.TheprincipleofthisCSistodepletethebatterytoaverylowSOCandthentriggertheICEtodrivethegeneratortorechargethebatterieswhilepoweringtheEM.Oncethebatteriesarefullyrecharged,theICEisshutoffagainuntilsuchneedsariseagain.Duringdeceleration,somebrakeenergyisrecoveredtohelprechargethebatterythroughregen-erativebraking.TheaimofthisCSistopropelthevehicleentirelyunderpureelectricalmodeasoftenaspossible.ThisgivestheadvantageofsettingtheICEtooperateatonepointoftorqueandspeedthatismostefficientandleastpolluting.ItalsopreventstheICEfromhandlingtransientloadswherethehighestlevelofemissionsisusuallyproduced.TheEMthatpropelsthevehicleunderalldrivingconditionswillhandlethetransientload.TheICEissettorunononlyonefixedgearratiothatiseitheroptimizedforfueleconomyorlowemissionwhendrivingthegenerator.Moreover,anotherpotentialemissionreduc-tionmaycomefromtheapplicationofanelectricallyheatedexhaustcatalystconverter.SincethereisampleknowledgeofwhentheICEwillbestarted,theexhaustcatalystconvertercanbeelectricallypreheatedtoreducecold-startemission[11].ThemajordisadvantageofthisCSisthatalloftheICE’spowermustbetransmittedthroughthegeneratorandthentotheEM.Duetotheinefficiencyofthesecomponents,someenergywillbelostduringenergyconversionfromoneformtoanother.ThisenergywillusuallynotbelostiftheICEisdirectlyusedtomechanicallydrivethewheelsasinconventionalvehicles.Besides,thisCSrequiresbothanEMandagenerator,whichusuallyresultsinamorecostlyandheaviervehicle.30.2.2SERIESPOWERFOLLOWERCONTROLSTRATEGYTheSeriesPowerFollowerCSdeterminesatwhattorqueandspeedtheICEshouldoperate.Electricalpowerisgenerated,accordingtothegivenconditionsofEM,batteries,ICE,andthepowerdemandedbythevehicle.ThisCSisusuallydesignedtomaximizefueleconomy,orminimizeemission,ormaximizebatterylife.TheICEmaybeturnedoffiftheSOCgetstoohigh,andturnedonagainifthepowerrequiredreachesacertainthreshold,oriftheSOChitstheminimumlevel.ThisCSalsoincorporatesregenerativebrakingtorecyclesomebrakeenergybackintothebatteriesduringvehicledeceleration.WhentheICEison,itspoweroutputtendstofollowthepowerrequired,accountingforlossesinthegeneratorsothatthegeneratoroutputpowerconvergeswiththepowerrequirement.Therefore,insomeinstances,theICEoutputpowermaybeadjustedbytheSOC,whichtendstobringtheSOCbacktothemiddleofitsoperatingrange,orjustkeep©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage661Friday,April8,20059:34AMtheSOCabovesomeminimumvalue.Atothertimes,theICE’soutputpowermightbekeptneartothepoweroftheICEatmaximumefficiency,orallowedtochangenofasterthanaprescribedrate.Thus,thisCSchangesaccordingtothepresetSOCconditionsandthepowerrequiredforpropellingthevehicle.Ingeneral,whentheSOCislowandthepowerdemandislessthanthepoweroftheICEatitsmaximumefficiency,thegeneratorisrunatapowerascloseaspossibletotheICE’smostefficientoperationpoint,withoutexceedingthesystemvoltagepowercon-straint.ThebatteriesarechargedasmuchaspossibletokeeptheICE’sefficiencyashighaspossiblewhilemaintainingamid-levelSOC.WhenthepowerdemandislessthanthepoweratmaximumefficiencyoftheICE,butgreaterthanthebatterychargepower,thegeneratorissettorunatapowerequivalenttotheICE’smostefficientoperationpoint.Therequiredpowerisusedtopropelthevehiclewhileexcesspowergeneratedisusedtochargethebatteries.Duringhigh-powerdemand,wheretherequestedpowerisgreaterthanthepoweratmaximumefficiencyoftheICE,thegeneratorissettorunatapowerequivalenttotheICE’smostefficientoperationpoint.Additionalpeakpowerisrequestedfromthebatteriestosatisfythetotalpowerrequested.Incitydrivingconditions,wheretheSOCishigh,theICEisshutoffandthevehicleoperatesunderpureelectricmodeasazeroemissionvehicle.TheadvantageofthisCSisthatthebatterypacksarerelativelysmallandtheSOCisalwaysmaintainedaroundamid-level.Ingeneralthisallowstheoverallweightofthepropulsionsystemtobelighter.ThedisadvantageisthattheICEisforcedtooperateatmultiplepointsinitsefficiencyandemissionmapstoadjustforloadchanges.ThiscausestheemissiontoincreaseastheoperationofICEmovesawayfromitsmaximumefficiencypoint.However,changingthethrottleslowlymaycompensateforthisnegativeeffect[6].30.2.3PARALLELICEASSISTCONTROLSTRATEGYTheParallelInternalCombustionEngineAssistCSusestheEMandbatteriesasthemainpowersourcetopropelthevehicle.ThisisatypeofparallelhybridconfigurationCS.TheICEisonlyactivatedduringlowSOC:accelerating,hillclimbing,andhighspeed.WhentheICEisoperatingitdirectlydrivesthewheelsmechanically,whilesimultaneouslyspinningthemotormechanicallyasageneratortorechargethebatteries.Duringdeceler-ation,thisCSallowsforregenerativebrakingtorecoverthebrakeenergybackintothebatteries.Underlow-powerandnormaldrivingconditions,thisCSwilloftendrivethevehicleunderpureelectricalmode.ElectricalpowerisderivedfromthebatterypackstopowertheEM.TheICEwillbeoperatedtodrivethevehiclewheneverthebatteriesaredepleted.Duringthesedrivingconditions,wheretheSOCislow,theICEwillreplacetheEMtopropelthevehiclemechanically,whileusingtheEMasageneratortorechargethebattery.Whenthebatteriesarefullyrecharged,theICEwillbeshutoffandthevehiclewillbedrivenelectricallyagain.Wheneverhighpowerisneededduringaccelerationorhillclimbing,theICEisusedtoassisttheEMbyprovidingadditionalpeakpowertofulfillthepowerdemand.Therefore,theICEisusuallyundersizedandoperatesnearfullloadconditionswhereitismostefficient.TheprimaryadvantageofthisCSisthatthevehicleisdrivenelectricallymostofthetime.Thus,ittendstoreduceoverallemissionsandtheamountoffuelusedifthebattery,EM,andICEareproperlysized.Italsoeliminatestheneedofanelectricalstarter,asthevehicleisalwaysmovingwhenevertheICEisstartedup.ThedisadvantageisthatemissionlevelsmaynotbeasgoodwhentheICEisoperating,becausetheICEusuallyoperatesduringhigh-loadconditionswhereemissionisthehighest.©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage662Friday,April8,20059:34AM30.2.4PARALLELELECTRICALASSISTCONTROLSTRATEGYTheParallelElectricalAssistCSisthemostcommonlyadoptedCSforparallelconfigu-rationHEVsduetoitsrobustnessandsimplicity.ThisCShasproventobereliable,asboththeHondaInsightandHybridHondaCivicadopteditastheirprimaryCS.ThisCSusestheICEtodrivethevehicle,whiletheEMisoftenusedforstartinguptheICEandassistingtheICEduringhigh-powerdemand.ThisconceptallowstheICEtooperateinamoreefficientregiontoreducefuelconsumption,whilekeepemissionslowbyavoidingfull-throttleconditionsusuallyneededforaccelerationandsteepgradient.Regenerativebrakingisincorporatedtohelpboosttheenergyefficiency,especiallyduringurbandrivingconditions.TherearetwodistinctwaysofusingtheEMtoassisttheICEunderthisCS,assummarizedinFigure30.4andFigure30.5.ThefirstmethodillustratedinFigure30.4usestheEMtostartuptheICEandtoassisttheICEduringhigh-performancedrivingconditions.Atlow-powerandnormaldrivingconditions,theICEisfullyresponsibleforpropellingthevehicleandrechargingthebatteries.Therefore,theICEwillbeoperatingwheneverthevehicleistravelling,exceptforidlingstops,deceleration,andcoastingdownhill.TheCSwillmaintaintheICEtooperatewithinitsmostefficientregionatalltimes.LowPerformanceDrivingCondition:EngineonlyNormalDrivingCondition:EngineonlyHighPerformanceDrivingCondition:EngineandElectricalMotorAssistEngineCut-offConditionIdlingStops,Deceleration,andCoastingDownHillFigure30.4ParallelElectricalAssistControlStrategy(firstmethod).LowPerformanceDrivingCondition:EitherEngineorElectricalMotor(SubjectedtoConditions)NormalDrivingCondition:EngineonlyHighPerformanceDrivingCondition:EngineandElectricalMotorAssistEngineCut-offConditionEngineTemperaturegreaterorequalto85degreeCelsiusAndSOC>SOCminimumAndLowVehicleSpeedorIdlingStopsorDecelerationorCoastingDownHillFigure30.5ParallelElectricalAssistControlStrategy(secondmethod).©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage663Friday,April8,20059:34AMThus,atlow-powerdrivingconditions,thebatterieswillrechargeasmuchaspossibletomaintaintheICEoperatingpointascloseaspossibletoitsmaximumefficiencypoint.Someexcessenergyisusedtopowertheon-boardelectricalaccessoriesloadaswell.Undernormaldrivingconditions,ICEisoperatingatitsmaximumefficiencypoint,andmostofthepowerisusedtopropelthevehicle,whiletheremainingpowerisusedtochargethebatteries.Whenadditionalpowerisneededduringhigh-performancedrivingconditions,theEMwillbeactivatedtoassisttheICEbyprovidingadditionalpeakpower.Therefore,theICEwillbemaintainedatitsmaximumefficiencypointwhiletheEMsuppliestheadditionalpeakpowerrequired.Duringdeceleration,theCSswitchestoregenerativebrakingmodetorecyclesomebrakingpowertorechargethebatteries.Around20%ofthetotalenergyconsumedbytheHEVisderivedfromregenerativebraking,whichimprovesfueleconomy.ThesecondmethodofutilizingtheEMtoassisttheICEunderthisCSissummarizedinFigure30.5.Duringlow-powerdrivingconditions,theICEproducesmorepowerthanneededtodrivethevehicle.ThisisduetothefactthattheCSisalwaystryingtomaintaintheICEtooperatenearitsmaximumefficiencypoint.SincetheexcessenergyproducedbytheICEunderlow-powerdrivingconditionsisunabletobestoredinthebatterieswhenevertheSOCishigh,someofthisenergywillbewasted,asnotallofitcanbeusedbytheon-boardelectricalaccessoriesload.Hence,topreventthisunnecessaryenergybeinglostduringlow-powerdrivingconditions,theEMwillbeusedtopropelthevehicleinsteadoftheICE.TheICEwillnotalwaysbeoperatedwheneverthevehicleistravelling.ThevehicletravellingspeedwilldeterminewhentheICEwillbeoperated.TheICEwillonlybeoperatedduringnormalandhigh-speeddrivingconditions.Duringlow-speeddriving,theCSwillpropelthevehicleunderpureelectricmodewhereonlytheEMisusedtodrivethevehicle.ICEwillonlybeusedtodrivethevehicleunderlow-powerdrivingconditionswhenevertheICEtemperaturedropsbelowacertainvalueortheSOChitsitsminimumlevel.ThisistoensurethattheICE’stemperatureisalwayskeptwarmedup,andtoavoidcoldstartingtheICEwhenitisneeded.Asthevehicle’sspeedincreasesaboveacertainthreshold,theICEwillbeturnedontoreplacetheEMinpropellingthevehicle.AtthisstagemostofthepowerproducedbytheICEoperatingatitsmaximumefficiencypointwillbeusedtodrivethevehicle,whiletheremainingpowerwillbeusedtospintheEMasageneratortorechargethebatteriesandpowertheelectricalaccessories.Athigh-speedorhigh-powerdemandtheEMwillbepoweredbythebatteriestoassisttheICEtopropelthevehiclebysupplyingtherequiredpeakpower.Throughthismethod,theCSwillefficientlymaintaintheICEtooperateatitsmaximumefficiencypointatalltimes.Regenerativebrakingisadoptedtofurtherimproveoverallenergyefficiency.Table30.1showsthatthesecondmethodhasabetterfueleconomythanthefirstmethod.Thefueleconomyimprovementismuchmoresignificant,especiallyforurbandrivecycles.Thereasonforthisisthaturbandrivecyclesinvolvelow-speedtravellingmostofthetime,whichfavorsthesecondmethod.Duringlow-speedtravellingthesecondmethodisoftenpropellingthevehicleunderpureelectricalmodeand,hence,reducingfuelconsumptionandemissionsignificantly.Besides,urbandrivecyclesinvolvemanyidlingstopsanddeceleration,whereregenerativebrakingandshuttingofftheICEduringidlinghelpsimprovetheoverallenergyefficiency.ThefirstmethodhashigherfuelconsumptionduetotheICEproducingmorepowerthanisneededduringslow-speedtravelling,astheCStendstomaintaintheICEatnearitsmaximumefficiencypoint.Asforhighwaydrivecycles,thefueleconomyimprovementisnotsosignificantwhencomparingbothmethods.However,thesecondmethodstillmaintainsaslightlybetterfueleconomy.Inhighway©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage664Friday,April8,20059:34AMTable30.1ComparisonofFuelEconomybetweentheFirstandSecondMethodDriveCycleFirstMethod(L/100km)SecondMethod(L/100km)USFTPcitycycle107.6USFTPhighwaycycle76.8Europeancitycycle9.98.8Extraurbancycle8.37.9Australianurbancycle11.39.6Melbournepeakcycle11.29Australiantruckhighwaycycle8.18Note:TheaboveresultsareobtainedfromasimulationmodeldevelopedusingADVISORsoftwarebyNREL.ThetestvehicleisbasedonaparallelhybridmodelconvertedfromanexistingconventionalFordFalconmodel.TheaboveresultsmeetthezerodeltaSOCrequirement.Table30.2ComparisonofPerformancebetweentheFirstandSecondMethodPerformanceFirstMethodSecondMethod0–96.6km/h8.2s8s64.4–96.6km/h3.2s3.1s0–137km/h14.7s14.4sMaximumacceleration3.8m/s23.8ms2Gradeability15.5%17.5%Maximumspeed221.5km/h221.5km/hNote:Objectiveofgradetesttoachieve12.5%gradeabilitywhilesustainingthevehicle’sspeedat88.5km/hfor82secwithadditional1000kgexternalloadonvehicletestmass.drivecycles,thevehiclewillbetravellingathighspeedmostofthetimewithnoidlingstops,thustherearefewerchancesforthevehicletobedriveninpureelectricalmode.TheeffectofshuttingofftheICEduringlowspeeds,asimplementedinthesecondmethod,isnotsorelevantinthehigh-speeddrivecycle,andhencethefueleconomyimprovementisnotsosignificant.Table30.2showsthatthesecondmethodhasaslightlybetterperformancethanthefirstmethod.ThereasonisthatthesecondmethodisslightlymoreefficientincontrollingandmaintainingtheICEtooperateatitsmaximumefficiencypointatalltimes.30.2.5ADAPTIVECONTROLSTRATEGYTheAdaptiveCSadjustsitscontrolbehaviorbasedonthecurrentdrivingconditionsthataffectboththeemissionsandfuelconsumption.Therefore,todeterminetheidealoperatingpointfortheICEandEM,theCSconsidersallpossibleICE–EMtorquepairs.ThisCS©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage665Friday,April8,20059:34AMattemptstooptimizethetorquedistributionbetweenICEandEMateachtimestep.Foragivenoperatingpoint,theCScalculatesthepossiblefuelconsumptionandemittedemission,togetherwiththeenergyneededtorestoretheSOCbacktoitsinitiallevel.TheCSalsotakesintoaccountuser-definedandstandard-basedweightingsoftime-averagedfueleconomyandemissionperformancetodetermineanoverallimpactfunctionforselectinganidealoperatingpoint.TheCSthencontinuouslyselectsthebestoperatingpointthatgivesthebestpossiblefueleconomywithminimumemission,whiletryingtorestoretheSOCbacktoitsinitiallevel.ThisCSgivestheadvantageofensuringthatthevehicleisalwaysmaintainingitsoptimalsettingsforoptimizingfueleconomyandemis-sionreductionunderalldrivingconditions.However,toimplementthisCSrequiresacontrollerwithaverylargecomputationalmemoryandprocessingpowerthatcanhandlehigh-speedandheavycomputationaldemandforupdatingthecontrolsystemwithinasplitsecond.ThisCSconsidersbothfueleconomyandemissioninitschoiceofoperatingpointsateachtimestep.Overthevalidrangeofoperatingtorques,theCSnormalizesallfivecompetingmetrics(i.e.,energyused,hydrocarbons,carbonmonoxide,nitrousoxides,andparticulatematteremissions)byusinguser-definedandstandard-basedweightingoftime-averagedfueleconomyandemissionperformancetodetermineanoverallimpactfunction.NexttheCSoptimizestheinstantaneousefficiencyoftheICE,exhaustremoval,EM,andbatteries.ItadjustsitsbehaviorbasedondrivingconditionssuchasICE,EM,batterytemperature,andamountofavailableregenerativebraking.Theamountofregenerativeenergyiscalculatedfromtimetotimeasthevehiclemoves.User-definedfueleconomyandemissionstargetsaretakenintoconsiderationaswell.AteachoperatingpointtheCSlooksattheentirerangeofpossibleICE–EMtorquecombinationstodetermineoptimumoperationpoint.Theimpactfunctionisminimized,andperformanceisdeterminedbytheweightedsumofinstantaneousfuelconsumption[12].ThefollowingdescribesthestepsforimplementingthisCS,andtheflowchartin[12](i.e.,Figure5ofReference12)summarizestheentireCSalgorithm:1.Definetherangeofoperatingpoints,representedbytherangeofacceptablemotortorquesforthecurrenttorquerequest.2.Foreachoperatingpoint,calculatetheconstituentfactorsforoptimization:•CalculatethefuelenergythatwouldbeconsumedbytheICE•Calculatetheeffectivefuelenergythatwouldbeconsumedbyelectrome-chanicalenergyconversion•Calculatethetotalenergythatwouldbeconsumedbythevehicle•Calculatetheemissionsthatwouldbeproducedbytheengine3.Normalizetheconstituentfactorsforeachcandidateoperatingpoints.4.Applyuserweightingtoresultfromstep3.5.Applytargetperformanceweightingtoresultfromstep4.6.Computeoverallimpactfunction,acompositeofresultsfromsteps3–5,foralloperatingpoints.Theminimumoperatingpointcalculatedisthefinaloperatingpointtobeupdatedateachtimestep.30.2.6FUZZYLOGICCONTROLSTRATEGYTheFuzzyLogicCSmimicshumanreasoningwheninterpretinginputsandoutputs,andmayberepresentedasasetofIF-THENrulesinawaythatisreadablebycomputers.Itisverydifferentfrombinarylogic,whichusesonlytwodistinctstates.Forinstance,when©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage666Friday,April8,20059:34AMTable30.3FuzzyLogicRule1.IfSOCisatMaximumlevelThenPgenis0kW2.IfSOCisNormalandPdriverisNormalandωEMisOptimalThenPgenis10kW3.IfSOCisNormalandωEMisnotOptimalThenPgenis0kW4.IfSOCisLowandPdriverisNormalandωEMisLowThenPgenis5kW5.IfSOCisLowandPdriverisNormalandωEMisNotLowThenPgenis15kW6.IfSOCisatMinimumlevelThenPgenisPgen,max7.IfSOCisatMinimumlevelThenScaleFactoris08.IfSOCisNotatMinimumlevelandPdriverishighThenPgenis0kW9.IfSOCisNotatMinimumlevelThenScaleFactoris1Note:AdaptedfromReference9.interpretingthespeedofavehicleasinput,binarylogiccanonlycategorizethevehicle’sspeedinputaseitherfastorslow.However,fuzzylogicusescontinuouslyvaryingdegreesofstatesormembershipfunctions.Therefore,vehiclespeedinputcanbeextremelyslow,slow,normal,fast,andextremelyfast.Thefuzzylogiccontrollerassignsmembershipgradestovariables.Itmayinterpretananaloguespeedof120km/htobe75%fastand30%extremelyfast.Thus,theCScanvarythethrottletobewideopen,mediumopen,orslightlyopen,dependingonthepresetrules.Inautomaticcruisecontrolsystems,ifthevehicle’sspeedfallsunderpartofthefastandtheextremelyfastcategories,thefinalthrottleopeningwillbeadjustedaccordingtoacombinationofsomepercentagesofmediumopenandslightlyopentoslowdownthevehicle.SincedrivingconditionsandvehicleloadsarehighlynonlinearandcannotbeexplicitlydescribedwhenconstructingaCSofanHEV,itisverydifficulttodeterminewhentocontroltheEMtoassistthedrivingtorqueorrechargethebattery.Besides,adifferentdriver,whohashisorherowndrivingpatterns,willyielddifferentwaysofhandlingthevehicle.Hence,iftheCSwerefollowedinadeterministicway,theobjectivesofoptimizingfueleconomyandemissionsreductionaswellasSOCbalancemaynotbeachieved.TheFuzzyLogicCSisusefulincontrollingnonlinearanduncertainsystemssuchasHEVapplication,anditisimmunetovariousvehicleloadandroadconditions[5].IntheFuzzyLogicCS,fuzzificationisthefirststepistodeterminethesetofrules(Table30.3)andmembershipfunctions(Figure30.6,Figure30.7,andFigure30.8)thatallowthecontrollertohaveafuzzyreasoningmechanism.Thesecondstepistodeterminethedegreeoffulfillmentfortheantecedentofeachruleusingfuzzylogicoperators.Thisdegreeoffulfillmentdeterminestowhichdegreethenthruleisvalid.Oncethisdegreeoffulfillmentisdetermined,itisusedtomodifytheconsequentrulesaccordingly.Thisisusuallydonebymultiplyingthedegreeoffulfillmentwiththeconsequentofnthrule.Thefinalstepisdefuzzification,wheretheresultsoftheinferencesteparecombinedintoasinglevalue.Thisisdonebyaveragingtheinferenceresultsweightedbythedegreeoffulfillmentoftherules.Inferenceandaggregationcanbecombinedintoasingleequation,whereKisthenumberofrules,Aisthedegreeoffulfillment,andCistheconsequentofnthrule[4,9].kkUAjn=∑∑CAnn(30.1)n==11n©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage667Friday,April8,20059:34AM1.21NormalHigh0.80.60.4DegreeofMembership0.20020406080100120DriverPowerCommand(kW)Figure30.6Driverpowercommandmembershipfunction.1.2Normal1TooLowLowTooHigh0.80.60.40.2DegreeofMembership000.20.40.60.811.2BatteryStateofChargeFigure30.7Batterystateofchargemembershipfunction.1.2Optimal1LowHigh0.80.60.40.2DegreeofMembership002004006008001000ElectricMotorSpeed(rad/s)Figure30.8Electricalmotormembershipfunction.AsimplifiedblockdiagramofthisFuzzyLogicCSisdepictedinFigure30.9.Thesignalsfromtheacceleratorandbrakepedalsarenormalizedtoavaluebetween0and1.Zerorepresentsthepedalisnotpressed,whileonerepresentsthepedalisfullypressed.Thebrakingsignalisthensubtractedfromtheacceleratingsignal,thusgivingthedriving©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage668Friday,April8,20059:34AMVehicleInternalSpeedCombustionDriver’sPowerDriverEngineDriver’sCommandCommandPowerCommandInterpreterGeneratorIce&PowerEMFuzzyPowerBatteryStateofLogicElectricChargeControllerScalingMotorPowerElectricMotorFactorSpeedFigure30.9FuzzyLogicControlStrategyschematicdiagram.inputsvaluebetweentherangeofnegativeoneandpositiveone.Thenegativepartofthedriverinputissenttothebrakecontroller,whichcomputestheregenerativebrakingandfrictionbrakingpowerrequiredtodeceleratethevehicle.Thepositivepartofthedriverinputismultipliedbythemaximumavailablepoweratthecurrentvehiclespeedsothatallpowerisavailabletothedriveratalltimes.ThemaximumavailablepoweristhesumofmaximumavailableICEandEMpower.Afterdriverpowercommandisdetermined,theFuzzyLogicCScalculatestheoptimalgeneratorpowerfortheEMwhenitisusedtorechargethebatteriesandascalingfactorfortheEMwhenitisusedasamotor.Thescalingfactorfallsbetweentherangeofzeroandone.WhenthescalingfactoriszeroitindicatesthattheSOCistoolowandtheEMshouldnotbeusedtodrivethewheels,topreventdamagingthebatteries.However,whentheSOCishighthescalingfactorequalsone.Powerdemand,SOC,andEMspeedarethemaininputstotheFuzzyLogicCS,asshowninFigure30.9.Figure30.6presentsthemembershipfunctionforpowerdemand.FuzzysetNormalrepresentspowerrangefornormalorlow-speeddrivingconditions.Highrepresentspowerrangeforhighaccel-erationandhighspeed.Thepowerdemandrange,from30kWto50kW,isthetransitionbetweennormalandhigh-powerdemand.Figure30.7presentsthemembershipfunctionforSOC.FuzzysetsTooLowandTooHighrepresenttherangesthattheSOCshouldavoid.FuzzysetNormalrepresentstheidealrangewheretheSOCshouldbe,andLowactsasabufferrangebetweenNormalandTooLowfuzzysets.Figure30.8presentsthemembershipfunctionforEMspeed.FuzzysetOptimalrepresentstheoptimalspeedrange.HighandLowfuzzysetsrepresentEMspeedtoohighandtoolow,respectively.Thetransitionrangeisverynarrow,astheEMefficiencyusuallydropsrapidlywhenthespeedisoutsidetheoptimalrange.FromtherulebaseinTable30.3,iftheSOCistoohighthedesiredgeneratorpower(Pgen)willbezero,topreventoverchargingthebatteries.IfSOCisnormalthebatterywillonlybechargedwhenboththeEMspeedisoptimalanddrivepowerisnormal.IfSOCdropstoolow,thebatterywillbechargedatahigherpowerlevel.ThisistoensureafastrechargeofSOCtoalwaysmaintaintheSOCwithinitsoptimaloperatingrange.IftheSOCdropstoolow,thedesiredgeneratorpowerissettomaximumavailablepowerandthescalefactorisdecreasedtozero.Thisistorechargethebatteriesasfastaspossibletopreventdamagingthem.ThefinalruleistopreventtheICEfromrechargingthebatterieswheneverthepowerdemandishighandtheSOCisnottoolow.UnderthisconditiontheEMshouldbeusedtoassisttheICEinprovidingpeakpowertoensurethattheICEis©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage669Friday,April8,20059:34AMoperatingatitsmaximumefficiencypointanditspowerlevelisnotshiftedoutsideitsoptimalrange.WhenevertheSOCisnottoolow,thescalingfactorissettoone.Finally,theCSdeterminestheICEandEMoutputpowerbyusingthepowerdemand(Pdriver),generatorpower(Pgen),andthescalingfactor(Sf).TheICEpoweristhesumofpowerdemandandgeneratorpower,asinthefollowingequation.PICE=Pdriver+Pgen(30.2)TheEMpoweristhereversepowerofthegenerator,thusisnegativeofdesiredgeneratorpower.PEM=–Pgen(30.3)Whenthepowerdemandislessthanthethresholdvalue,whichisthescalingfactormultipliedby6kW,theHEVwillbedrivenunderpureelectricmodetopreventtheICEfromoperatingoutsideitsefficientrange.Therefore,theICEoutputpowerissettozero,whiletheEMoutputpowerissettoavalueequivalenttothetotalpowerdemand.WhenthepowerdemandisgreaterthanthemaximumICEoutputpoweratcurrentenginespeed,theICEoutputpowerissettothemaximumavailablepoweratcurrentenginespeed.FortheEM,itsoutputpowerissettoavalueequivalenttothetotalpowerdemandminusthemaximumICEoutputpoweratcurrentenginespeed.WhenevertheEMisusedasamotortoassisttheICE,whichmeanstheEMpowerispositive,itmustbemultipliedbythescalingfactortodeterminethepeakpowerrequiredfromtheEM.30.3POWERELECTRONICCONTROLSYSTEMANDSTRATEGYThemainfunctionoftheelectroniccontrolleristoadjustcontrolparametersforthesmoothoperationofthepartsandselecttheoptimummodeofoperationunderalldrivingcondi-tions.Ingeneral,thebasicpowerelectronicscomponentsessentialforHEVareconverterandmotordrive,DC-linkbrakeresistor,DC-linkmainconnector,batterycharger,andboardpowersupply.Theconverterandmotordriverworktogetherinconvertingandcontrollingtheenergyflowbetweentheenergysourceandtheelectricaldrive.ThefunctionoftheDC-linkbrakeresistoristotakeoverpartoftheenergythatcannotbestoredinthebatterieswhentheSOCistoohigh.Ifthisexcessenergywerenotremoved,itwoulddamagethepowerelectronicsbyraisingtheDC-linkvoltage.Besides,withDC-linkbrakeresistorsaconstantbraketorquecanbemaintained,evenifthebatteryisalreadyfullycharged.Forsafetyreasons,themainconnectoractsasabuffertoseparatetheenergystorageandthedrivesystem.Incaseoffailurethedisconnectionofdrivesystemfromenergystoragehastobetriggeredautomatically.Besideschargingthebatteries,thebatterychargermonitorstheSOCandactsasabatterymanagementsystemtopreventthedamageofbatteryduetooverloadordeepdischarge.Theon-boardpowersupplyconvertstheenergyfromthemainenergysourcetotheconventional12Velectricalenergysupplyconsumedbythevehicle’selectricalaccessories[1].ThedevelopmentofCSinHEVistoaddressthespecializedneedsofhybridvehiclesinpowermanagement,asthereisalwaysatradeoffbetweenenergyefficiencyandemis-sions[12].Ingeneral,CSsdevelopedforHEVareclassifiedintothreecategories.ThefirsttypeofCSinvolvescontroltechniqueslikebang-bangcontroltechniques,rule-based©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage670Friday,April8,20059:34AMAcceleratorpedalBrakepedalpositionsignalpositionsignalVehiclespeedVehiclecontrollerBatterySOCMotorPowerEngineFrictionbrakecommandpowerpowercommandMotorcommandFrictionEnginecontrollerbrakecontrollercontrollerVoltageFrequencyEnginethrottlepositioncommandFrictionMotorbrakingEnginepowerMotoringRegeneratingEnginepowerbrakingpowerpowerTorquecoupler&TransmissionWheelsFigure30.10AgeneralcontrolschematicdiagramofanHEV.fuzzylogic,andloadfollowercontroltechniquesforcontrolalgorithmdevelopment.Thesecondapproachutilizesstaticoptimizationmethods,wheretheoptimizationschemedeterminestheproperenergyandpowersplitbetweenthetwoenergysourcesundersteady-stateoperation.Thelastapproachtakesintoaccountthedynamicnatureofthesystemwhenperformingtheoptimization.Thisoptimizationisdonewithrespecttotimeratherthanforafixedpointintime,thusdynamicoptimizationwillbemoreaccurateundertransientconditions.However,thisapproachhasextremelyhighcomputationalcostsandissophisticatedtoimplement.ThefunctionofthehybridcontrollerinanHEVistoimplementtheCStomanagethedistributionofdesiredpropellingpowerfromtwodifferentpowersourcesundervariousdrivingconditions.DifferentCSsimplementedbythehybridcontrollerwouldresultindifferentfueleconomy,performance,andemissionscharacteristics.However,allCSshavesimilarcontrolmodesthataretargetedtohandleallpossibledifferentdrivingconditions.DifferentCSsareonlyamatterofdifferentcombinationsandsequencesofutilizingthesecontrolmodesinhandlingdifferentdrivingconditions.Figure30.10showsanoverallconfigurationofageneralHEVhybridcontrollerthatiscapableofimplementingtheCS.Thefollowingaredescriptionsofallthecontrolmodesforhandlingallpossibledrivingconditions.ThepropellingmodeiscategorizedintoEMonlymode,hybridpropellingmode,batterychargingmode,andICEonlymode.Whentheacceleratorisfullyreleased,thevalueofacceleratorposition,Caiszero.Whiletheacceleratorisfullydepressed,thevalueofCaisone.Cavalueiswithintherangeofzeroandone.Therefore,thepoweroutputfromthedrivetrainisexpressedasthefollowingequation,wherePpisthepoweroutputatacceleratorcommandandPpmaxisthemaximumpowerofthedrivetrain,whichisthesumofICEandEMmaximumoutputpower.©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage671Friday,April8,20059:34AMPP=CaPpmax(30.4)Accordingtothispowercommandandfeedbackparameters,suchasvehiclespeed,enginespeed,motorspeed,andbatterySOC,thehybridcontrollergivesrelevantcom-mandstotheICEcontroller,EMcontroller,andbrakecontrollertotakenecessaryactions.TheICEoutputpowerPecanbeexpressinthefollowingequation,whereCe(0<=Ce<=1)isICEpowercommandandPemaxisthemaximumICEpoweravailable.WhenCeiszerotheICEthrottleisfullyclosed,whilewhenLeisonethethrottleisfullyopen.Pe=CePemax(30.5)TheEMoutputpowerPmisexpressedinthefollowingequation,whereCm(–1<=Cm<=1)isthemotorpowercommandandPmmaxisthemaximumpowerofthemotor.WhenCmislessthenzerotheEMoperatesasagenerator,andwhenCmisgreaterthanzerothemotorfunctionsinmotoringmode.Wheneverthevehiclespeedislessthantheminimumspeedoftheengine,theCSwillbeoperatinginEMOnlyMode.Underthismodethemotorwillbetheonlypowersourcetopropelthevehicle.Therefore,thefinalpoweroutputPp=PmandCm=Ca,whileCe=0.UnderHybridPropellingMode,theEMwillbeusedtoassisttheICEinpropellingthevehicle.TheICEwillonlyoperateatitsmaximumefficiencypointandmaintaintheICEoutputatitsmaximumavailablepower.TheEMwillbeusedtoprovidethepeakpowertomeetthetotalpowerdemand.Therefore,Pm=Pp–PemaxwhereCm=Pm/Pmmax.WhenthepowerdemandofthevehicleislessthanthemaximumICEoutputpowerandtheSOCisnotfull,theICEwillrunatfullthrottleandtheremainingpowerisusedtorechargethebatteries.Thus,theCSwillbeoperatinginBatteryChargingMode.UnderthismodethePm=Pemax–Pp,andCm=–Pm/Ppmax.WhenthepowerdemandislessthanorequaltothemaximumICEpowerandthebatteriesarefullycharged,thevehiclewillbepropelledunderEngineOnlyMode.Therefore,theEMwillbeshutoffandPm=0withCm=0.ICEoutputpowerwillbeequivalenttothevehiclepowerdemandwherePe=PpwithCe=Pe/Pemax.DuringBrakingModetheacceleratorpedalwillbefullyreleased,andthebrakepedalisdepresseddependingonhowmuchbrakingisrequiretodeceleratethevehicleorbringthevehicletoastop.ThefractionofmaximumbrakingpowerCb(0<=Cb<=1)isthesignalfromthebrakepedaldemandingbrakepower.WhenCb=1thebrakepedalisfullydepressed,andwhenCb=0thebrakepedalisfullyreleased.ThetotalbrakepowerdemandPbisexpressedinthefollowingequation,wherePbmaxisthemaximumbrakepowerdemandofthevehicle:Pb=CbPbmax(30.6)TheBrakingModecanbeclassifiedintotwocategories,whichisthePureRegen-erativeBrakingModeandHybridBrakingMode.PureRegenerativeBrakingModeonlyappliestodrivelinebraking.However,HybridBrakingModerequiresfrictionbrakingtoassistsdrivelinebrakingtodecelerateandtostopthevehicle.Indrivelinebraking,theelectricbrakepowerPmisexpressedinthefollowingequation,wherePmmaxisthemaximumbrakepowersuppliedbytheelectricalmachine(i.e.,EMasitisalsousedasageneratorinHEV)whendrivenbythedriveline.Pm=–CmPmmax(30.7)Asforfrictionbraking,themechanicalfrictionbrakepower,Pfbisexpressedinthefollowingequation,whereCfb(0<=Cfb<=1)isthefractionofthemaximummechanical©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage672Friday,April8,20059:34AMfrictionbrakepower.Pfbmaxisthemaximummechanicalfrictionbrakepower,whichisthedifferencebetweenthemaximumbrakepowerdemandandthemaximumelectricregen-eratingbrakeforce.Pfb=CfbPfbmax(30.8)UnderPureRegenerativeBrakingMode,vehiclebrakepowerdemandPbislessthanthemaximumbreakpowerofdrivelinebraking.Alltheneededbrakingpowerofthevehiclewillbefullybornebythedrivelinebrakingwhentheregenerativebrakingtakesplace.Therefore,underthissituation,thebrakepowerdemandcanbeexpressedasPb=–PmwhereCm=–Pm/Pmmax.Wheneverthevehiclebrakepowerdemandisgreaterthanthemaximumbrakepowerofdrivelinebraking,HybridBrakingModetakesplace.TheRegenerativeBrakingModeshouldalwaysbeusedfirst,forthepurposeofenergysaving.Thefrictionbrakingmustthenbeactivatedtoassistthedrivelinebrakingbysupplyingtheremainingbrakepowertodeceleratethevehicleorbringittoastop.ThebrakepowersupplybythemechanicalfrictionbrakesystemcanbeexpressedasPfb=Pb–PmmaxwhereCfb=Pfb/Pfbmax[8].Inconclusion,themaintaskofthehybridcontrolleristoimplementtheCSandfunctionasalogicalcontrolunit.ItsmaintaskistosendcommandstolowerlevelcontrollerssuchastheICEthrottlecontroller,motorcontroller,andbrakecontroller.Toensurecorrectcommandsaregivenouttoeachcomponent,themaximumcapabilityofeachcomponentmustbestoredinthevehiclecontroller.ThisinformationismaximumICEpowercurve,maximumEMmotoringpowerandregeneratingpower,aswellasmaximumvehiclebrakepowerdemand.Thisinformation,togetherwiththelogiccontrol-ler,willenablethehybridcontrollertoimplementallsortsofCSstomanagetheenergyflowandconversionwithinanHEV.30.4CURRENTHEVSANDTHEIRCONTROLSTRATEGIESAnHEV’sfueleconomyandemissionsdependonthewayelectricalenergystoredinthebatteriesissubstitutedbythechemicalenergyoffuel,oronthewaytheICEneedstoprovideextraenergytorechargethebatteries.Therefore,aCSisneededformanagingtheenergyflowandconversionefficiently.TheCSimplementationishandledbytheelectroniccontrollerunit(ECU),wherevariousfactorslikeSOC,vehicledynamics,andcharacteristicsaswellasparametersofvariouscomponentsaretakenintoconsideration.TheECUthencommunicateswiththelowerlevelcontrolunitofeachspecificcomponentsuchasthemotorcontroller(MC),enginemanagementcontroller(EMC),andbatterychargeraswellasconverter,tocontroltheHEVbasedontheselectedCS.ThefollowingsectionswilldiscusstheCSadoptedbytheHondaInsightandToyotaPriusfortheirrespectivepowermanagementsystems.30.4.1HONDAINSIGHTUnlikethedefaultparallelhybridCS,theHondaInsightCSusesthedirectsplitofthetorquesignal,wherethecontrollerdirectlycommandsthetorquefromtheICEandEM.InthedefaultparallelhybridCS,theICEsuppliesallthedemandtorque,andonlytheunmettorqueisdrawnfromtheEM.InInsight’sCS,thereisaseparatetorquecommandsenttotheEMdirectly.ThisistoensurethattheEMprovidesthecorrectamountoftorquedemandedbytheCS.ThetorquecouplerwillsumupthetorquesfromtheICEandEM,andsendthemtothetransmissiontodrivethewheels.©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage673Friday,April8,20059:34AMDuetothehybridarchitectureoftheHondaInsight,itdoesnotallowforpureelectricdriving.WheneverthevehicleistravellingtheICEwillbeoperated,exceptfordecelerationandcoastingdownhill.Duringlow-speedandpowerdriving,theICEwilloperateasneartotheICEmaximumefficiencypointaspossiblebyrechargingtheICEasmuchaspossible.Excesselectricalenergyisalsousedtopowertheon-boardelectricalaccessories.Undernormaldrivingconditions,theICEwillbeoperatedatitsmaximumefficiencypoint,whereallpowerwillbeusedtodrivethevehicle;theexcessenergyisthenusedtorechargethebatteries.Athigh-speedandpowerdrivingconditions,theEMwillbeusedtoassisttheICEtoachievetherequestedpower.Therefore,theICEwillbeoperatedatalltimeswheneverthevehicleisdriving.Duringdeceleration,regenerativebrakingisusedtorecoversomebrakeenergybackintothebatterypackstoimproveenergyefficiency.SincetheHondaInsightCSusesthedirectsplitofthetorquesignal,thecontrollerdecidesthetorquecontributionoftheICEandtheEM.Basedonthetotaltorquerequest,andthecharacteristicofthemotor,thecontrollerdecidesthecontributionoftheEM.TheremainingunmettorquerequestissuppliedbytheICE,uptoitsmaximumtorquelimit.Ifthetwosourcesactingsynergisticallycannotmeetthetorquedemand,theperformanceofthevehiclewilldegrade.IntheHondaInsight,thebatterypackSOClimitsaresetwithinarangeof20to80%.WhentheSOCisnearthelowerlimits,theCSreducestheamountofelectricalassist.AstheSOCreaches20%(i.e.,thelowerboundarylimit),noassistisallowed,topreventoverdischarginganddamagingthebatterypacks.Similarly,iftheSOCreachesitsupperboundlimit(80%),allregenerationbytheEMisstoppedtopreventoverchargingthebatteryanddamagingthesystem[7,10].30.4.2TOYOTAPRIUSToyota’sPriuscombinesthefeaturesofbothaseriesandparallelHEV.ItrechargesitsbatteriesprimarilybyusingtheICE,inadditiontoregenerativebraking.PriususesaplanetarygearboxfordividingtheICEoutput,plusageneratorandamotor.Thisplanetarygearboxalsoactsasacontinuouslyvariabletransmission(CVT)systemthatenablestheICEtooperateatitsmostefficientoperatingpointatalltimesandeliminatestheneedofaclutch.Approximately70%oftheICEtorqueisdirectedtothedriveaxlebymeansofacounter-gearanddifferential,throughwhichthemotorisalsoconnectedtothedriveaxle.Theremaining30%ofICEtorqueisusedtodrivethegenerator.AccordingtotheCS,thegeneratoroutputmaybedirectedeithertorechargethebatterypacksortopowertheEMforextradriveforce.ThegeneratoralsofunctionsasastarterfortheICE,resultinginaquietandseamlesssystem.ThePriushybridarchitectureisacombinationofseriesandparallelhybridconfig-uration,andhenceitismuchmoreflexiblethantheInsight’shybridarchitecture.ThePrius’sarchitectureallowsitsCStoimplementpureelectricaldrivemodewhenthepowerdemandisbelowacertainthreshold.Thisbooststheaverageefficiencyofurbandrivingbyincreasingtheefficiencyby40%.Thus,therewillbesignificantimprovementinfueleconomyandemissionreduction.ThefollowingisanoverallsummaryofPrius’sCSinhandlingallpossibledrivingconditions[3,10].•WhenICEdemandislow,suchasstarting,travellingatlightload,orcoastingdownhill,theCSdrivesthePriusunderpureelectricalmode,wheretheon-boardbatterypacksareusedtopowertheEM.•Duringnormaltravelling,theCSengagestheICEtodrivethewheelsandthegeneratortopowertheEMorrechargethebattery,dependingontheSOC.©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage674Friday,April8,20059:34AM•Atfullacceleration,theCSdirectsadditionalboostpowerfromthebatterytopowertheEMforassistingtheICEtoachievethepowerdemand.•Duringdecelerationorbraking,theCSturnstheEMintoagenerator,recoveringkineticenergyfromthewheelsintoelectricitytochargethebattery.•Wheneverthecarisidlingorthepowerdemandislow,theCSshutsofftheICE.TheICEisonlyoperatedwhenthebatteryneedschargingortopowertheairconditioning.30.5CONCLUSIONHybridCSandpowermanagementalgorithmsareessentialforallhybridvehiclestooperateattheirmostefficientstate.WithoutaCS,anHEVisjustanordinaryvehiclewithmorethanonepowersourcehardwiredtogether.Therefore,thevehiclewillnothavetheintelligencetooperateinitsmostefficientconditiontoachievethegoalsofHEV.WhenapplyingaparticularCS,thereisalwaysatradeoffbetweenfueleconomyandemissionsreduction.Thus,HEVsarespecificallydesignedtooperateinanoptimumoperationrange.Thisrangemaybedifferentifagivensituationrequiresoptimizingfueleconomyoremissionreduction.ACKNOWLEDGMENTThesecondauthoracknowledgestheRowdenWhiteFoundationinAustraliaforpartiallyfundingthiswork.REFERENCES1.A.Vezzini,K.Reichert.PowerElectronicsLayoutinaHybridElectricorElectricVehicleDriveSystem.IEEEworkshop0-7803-3292-X/96,1996.2.C.Lin,Z.Filipi,Y.Wang,L.Louca,H.Peng,D.Assanis,J.Stein.Integrated,Feed-ForwardHybridElectricVehicleSimulationinSIMULINKanditsUseforPowerManagementStudies.JSAE2001-01-1334,2001.3.D.Hermance,S.Sasaki.Hybridelectricvehiclestaketothestreets.IEEESpectrum,1998,p.4852.4.E.Cerruto,A.Consoli,A.Raciti,A.Testa.FuzzyLogicBasedEfficiencyImprovementofanUrbanElectricVehicle.JIEEE0-7803-1328-3/94,1994.5.E.Koo,H.Lee,S.Sul,J.Kim.TorqueControlStrategyforaParallelHybridVehicleusingFuzzyLogic.JIEEE0-7803-4943-1/98,1998.6.J.Marcinkoski,C.Whiteley,J.Goldman,R.Simons.1999UniversityofMarylandFutureCarDesignReport.JSAE,1999.7.K.Kelly,M.Zolot,G.Glinsky,A.Hieronymus.TestResultandModelingoftheHondaInsightusingADVISOR.JIEEE2001-01-2537,2001.8.L.Chu,Q.Wang,Y.Li,Z.Ma,Z.Zhoa,D.Lui.StudyoftheElectronicControlStrategyforthePowerTrainofHybridElectricVehicle.IEEEworkshop0-7803-5296-3/99,1999.9.N.Schouten,M.Salman,N.Kheir.FuzzyLogicControlforParallelHybridVehicles.JIEEETrans.1063-6536/02,2002.10.R.Trigui,F.Badin,B.Jeanneret,F.Harel,G.Coquery,R.Lallemand,JP.Ousten,M.Castagne,M.Debest,E.Gittard,F.Vangraefshepe,V.Morel,L.Baghli,A.Rezzoug,J.Labbe,S.Biscaglia.HybridLightDutyVehicleEvaluationProgram.JAutomotiveTech-nology1229-9138/012-02,2002.©2005byTaylor&FrancisGroup,LLC DK3023_book.fmPage675Friday,April8,20059:34AM11.T.Ciccarelli,R.Toossi.AssessmentofHybridConfigurationandControlStrategyinPlan-ningFutureMetropolitan/UrbanTransitSystem.FinalReport,METRANSTransportationCenter,CaliforniaStateUniversity,LongBeach,CA,2002.12.V.Johnson,K.Wipke,D.Rausen.HEVControlStrategyforReal-TimeOptimisationofFuelEconomyandEmission.JSAE2000-01-1543,2000.©2005byTaylor&FrancisGroup,LLC