Plug-in Hybrid Electric Vehicles

Electric vehicles (EVs) will revolutionise the automotive industry with their unique and innovative technology. But that revolution is at least a few years away from now. Although electric cars are gaining popularity, it’s not everyone’s cup of tea, especially in India. One of the closest alternatives to EVs is the Plug-in Hybrid Electric Vehicles (PHEV). They provide the flexibility of switching between electric mode and conventional engine mode.

1. Plug-in Hybrid Electric Vehicles
Dr.G.Nageswara Rao
Professor
Plug-in Hybrid Electric Vehicles
Dr.G.Nageswara Rao
Professor

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PHEVsandEREVsblendedPHEVs,PHEV
Architectures,equivalentelectricrangeofblended
PHEVs;FueleconomyofPHEVs,power
managementofPHEVs,end-of-lifebatteryfor
electricpowergridsupport,vehicletogridtechnology,
PHEVbatterycharging.

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Introduction to PHEVs
▪Plug-inhybridelectricvehicles(PHEVs)havethepotentialtodisplace
transportationfuelconsumptionbyusinggridelectricitytodrivethecar.
▪PHEVscanbedriveninitiallyusingelectricenergystoredintheonboard
battery,andanonboardgasolineenginecanextendthedrivingrange.
▪Inthe1990sandearly2000s,pureelectriccarswerenotsuccessful,one
ofthemajorreasonsbeingthelimiteddrivingrangeofthebattery-
poweredcarsavailableatthattime.
▪Forexample,theGMelectricvehicle(EV)hadarangeofabout100
miles(160km)andtheFordRangerelectrictruckhadarangeof
approximately60miles(96km).

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HowdoesaPlug-inHybridElectricVehicleWork?
▪PHEVvehiclesworkinthesamewayasconventionalhybrid
vehiclesgenerally.Thebiggerbatterypackthathastobeconnected
toanexternalelectricalsource,istheprimarydistinction.
▪Plug-inhybridautomobileoperatesonthefollowingpoints:
▪Normally,aPHEVcomesupinall-electricmode,wheretheelectric
vehicleautonomouslymovesthecarforward.
▪Untilthebatterypackrunsoutofpower,thecarwillremainrunning
entirelyelectrically.
▪Uponreachingdrivingspeeds,certainPHEVsautomatically
transitiontohybridmode(ElectricMotor+InternalCombustion
Engine).
▪Whenthebatterychargerunsout,theinternalcombustionengine
kicksin,andtheautomobilerunslikeregulargasolineordieselcar.
▪Thebatterypackisconnectedtoanexternalpowersource,which
beginschargingthevehicle.
▪Regenerativebrakingandtheinternalcombustionengineboth
assistinchargingthebattery.

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Criteria PHEV HEV BEV
Mode of OperationThe vehicle is
propelled by a
combination of an IC
engine and an electric
motor.
An electric motor
helps the traditional
Internal combustion
engine run more
efficiently or function
better.
The car is driven by
an electric motor.
Emission levels Compared to gasoline
and diesel
automobiles, they
emit fewer
greenhouse gases.
Lesser carbon
footprints than those
of traditional cars.
There are no
pollutants from their
tailpipes.
Charging The recharging period
is less since battery
packs are more
compact.
There is no
requirement for
recharging because
the battery pack is
charged while the car
is moving due to
regenerative braking
or a generator.
Battery packs in
BEVs are bigger.
Thus, the charging
time extends.
Price High Low Low

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Advantages of Plug-In Hybrid Electric Vehicles
▪PHEVshavenopollutantswhenoperatingexclusivelyonelectricity.
▪Whencomparedtonormalpetrol/dieselautomobiles,theyemitless
CO2intotheatmosphere.
▪Theelectricvehiclehelpsthemotor,makingplug-inhybridvehicles
propellantatslowerspeeds.
▪Ifyouonlytraveldomestically,thentheoperatingcostsarecheap.
▪Thereisnoreasontoworryaboutmileageastheinternal
combustionenginecanhandlevastintervals.
Disadvantages of Plug-In Hybrid Electric Vehicles
▪PHEVsaremorecostlythantraditionalandregularhybridvehicles.
▪Duringlengthyhighwaytrips,thefuelusagecanbecomparableto
thatofaregularcar.
▪Thedecliningbatterylifemightharmtheefficiencyofpureelectric
vehicles.
▪Regardlessofthetypeofcharger,thebatterychargesinafewhrs.
▪Electricvehiclecanbeexpensivetofix.

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Parameters PHEVs BEVs
Working principle
An electric motor and IC engine work
independently or in tandem to propel
the vehicle.
An electric motor propels the
vehicle.
Electric range
The pure electric range is limited or
lesser than BEVs due to a smaller
battery pack.
Since BEVs rely on pure
electric power, they comprise
larger battery packs. Hence,
the electric range is greater
than PHEVs.
Emissions
They produce lower carbon emissions
than conventional petrol/diesel cars.
They produce zero tailpipe
emissions.
Charging time
Since the battery packs are smaller in
size, the charging time reduces.
BEVs have larger battery
packs. Hence, the charging
time increases.
Running cost High Low
Vehicle price Expensive but costs less than BEVs.Expensive

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Parameters PHEVs HEVs
Working principle
An electric motor and an IC
engine propel the vehicle,
wherein they can operate
independently or in tandem.
An electric motor assists the
conventional IC engine in
improving fuel efficiency or
performance.
Electric range Limited
Typically, an HEV cannot
operate in pure electric mode.
However, some HEVs do offer
pure EV mode at slow speeds
for limited distances.
Emissions
They produce lower carbon
emissions compared to petrol
and diesel cars.
Lower carbon footprints
compared to conventional
vehicles.
Charging
They need to be plugged into
an external power source to
charge the battery pack.
No need for charging; since the
battery pack gets charged
within the vehicle via
regenerative braking or a
generator.
Battery pack
They comprise larger battery
packs.
HEVs come with smaller
battery packs.
Running cost Low High
Vehicle price Expensive than HEVs. Affordable than PHEVs.

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PHEVs and EREVs
▪PHEVsaresometimescalledrange-extendedelectricvehicles
(ReEVs)orextendedrangeelectricvehicles(EREVs),inthe
sensethatthesevehiclesalwayshaveon-boardgasolineordiesel
thatcanbeusedtodrivethevehicleforanextendeddistance
whentheon-boardbatteryenergyisdepleted.
▪Furthermore,thesevehiclescanprovidehighfueleconomyduring
theextendeddrivingrangeduetothelargebatterypackthatcan
acceptmoreregenerativebrakingenergyandprovidemore
flexibilityforengineoptimizationduringtheextendeddrivingrange.
▪However,EREVs,suchastheGMChevyVolt,mustbeequipped
withafull-sizedelectricmotorsothatpureelectricdrivingcanbe
realizedforallkindsofdrivingconditions.
▪Itisshownthat,forsomedrivingconditions,all-electricdrive
sometimesdoesnotprovidethemostbenefits,giventhelimited
batteryenergyavailable.

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Types of PHEVs
1. EREV Type 2. Blended Type

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EREV Type

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Series Configuration
PHEV Architectures

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FigureshowsthearchitectureofaseriesPHEV.Intheseriesconfiguration,the
gasolineengineoutputisconnectedtoagenerator.Theelectricitygeneratedbythe
generatorcanbeusedtochargethebatteryorsupplypowertothepowertrain
motor.Theelectricmotoristheonlycomponentdrivingthewheels.Themotorcan
beaninductionmotor,aswitchedreluctancemotor,orapermanentmagnetmotor.
Themotorcanbemountedonthevehicleinthesamewayasinaconventional
vehicle,withouttheneedfortransmission.In-wheelhubmotorscanalsobe
chosen.Intheseriesconfiguration,themotorisdesignedtoprovidethetorque
neededforthevehicletodriveinallconditions.Theengine/generatorcanbe
designedtoprovidetheaveragepowerdemand.
ParallelandcomplexhybridscanbedesignedasPHEVsaswell.Inparalleland
complexconfigurations,theengineandthemotorcanbothdrivethewheels.
Therefore,themotorsizecanbesmallerthanthoseinseriesconfigurations.In
comparisontoregularhybridelectricvehicles(HEVs),aparallelorcomplexPHEV
willhavealarger-sizedbatterypackthatprovideslongerdurationforextended
electricdrive.Theengineisturnedonwheneverthevehicle’spowerdemandis
high.

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❑IntheEREVspecification,thecarcomeswitha1.5literturbo-
charged4-cylinderenginewith123hp-thatpowerdoesn’t
countthoughtowardsthetotaloutputofthevehiclesinceitisn’t
connectedtothewheels.
❑Thebatteryhas40kWhcapacityandoffers140kmofelectric-
onlyrange.Afterthattheextenderkicksingivingthecaratotal
rangeofover1,000km.TheEREVisavailableintwoversions
withthelatterhavingtwoelectricmotorswithtotalpoweroutput
of315kWand720Nmoftorque-theresultingsprintfrom0to
100km/htakesjust4.4seconds.
❑Theclaimed1,000kmrangemeansthatthecaruses56litersof
fueltocover860kmwhichgivesusatheoreticalconsumptionof
6.5l/100km

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▪Extended-rangeelectricvehicles(EREVs),commonlyknownasseries
hybridelectricvehicles(Series-HEV),havebetterautonomythanelectric
vehicles(EV)withoutrangeextenders(REs).
▪EREVscangofromonecitytoanotherormakelongjourneysingeneral.In
recentyears,EREVshaveattractedconsiderableattentionbecauseofthe
necessitytoimproveautonomyusingnewanddifferenttechnologiesto
generateextraenergyforEVs.
▪Today,fossilfuelsmeettheneedsofthetransportationsectortoasignificant
extent,butbringonvariousadverseeffects,suchasairpollution,noise,and
globalwarming.
▪Comparedtointernalcombustionenginevehicles(ICEVs),EREVsreduce
emissionsandareconsideredafavourablealternative.
▪EREVs,comparedwithEV,notonlyhavetheadvantageof“zerofuel
consumptionandzeroemissions”theyalsoeffectivelysolvetheproblemof
havinganinadequatedrivingrangeduetopowerstoragelimitationsin
batteries

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ExtendedRangeElectricVehicleTechnology
▪Arangeextender(RE)isasmallelectricitygenerator(APU)which
operateswhenneededasasolutiontoincreaseautonomyinEVs.
▪ThemaincomponentsoftheREarethegeneratorandinternalor
externalcombustionengine;theinternalorexternalcombustion
engineiscoupledtothegeneratorinaseriesconfiguration.
▪TheprimaryfunctionoftheREforanEVistoextendthevehicle’s
mileage.OperationoftherangeextenderisinitiatediftheSOC
(stateofcharge)oftheEVsbatterydropsbelowaspecifiedlevel.
▪Inthissituation,theengineprovideselectricitybyrechargingthe
batteryordirectlydrivingtheEVduringtravelandcontinuesthe
vehicle’soperation.
▪Thedifferenceinaplug-inhybridelectricvehicle(PHEV)isthat
theelectricmotoralwayspropelsthewheels.
▪Theengineactsasageneratortorechargethevehicle’sbattery
whenitdepletesorasitpropelsthevehicle.

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▪Aseriesconfigurationisusedasthemainsystem,whichisconsideredan
APU.
▪Thesystemisconnectedtoseveralsubsystems,suchasthegenerator,
battery,electronicmanagementsystem,andelectricmotor.
▪Theelectricmotorconvertselectricalenergyfromthebatteryto
mechanicalpower.
▪ItpropelsthewheelswhiletheAPUgenerateselectricenergytorecharge
thebattery.Finally,theelectronicmanagementsystemcontrolsallthe
systemsforoptimalfunctioning.
▪TheEREVhastwooperationmodes:pureelectricvehicleandextended-
rangemode.Ifthedistanceisshort,thevehicleoperatesinpureelectric
vehiclemodewithouttheRE.
▪Ifthedistanceislong,thevehicleoperatesinextended-rangeelectric
vehiclemode.
▪TheREisoffaslongasthereissufficientenergyinthebatteryforpurely
electricdriving,andactivatedwhenevertheSOCdropsbelowacertain
level.TheREworksuntilthedesiredSOCisachieved.Thebatterypower
managergivesthisfunction.

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Technological Classification of EREV
TheelectricpropulsionsystemistheheartofanEREV.Itconsists
ofthemotordrive,atransmission(optional)device,andwheels.
Therearethreekindsofelectricmotors:directoralternating
currentandin-wheelmotors(alsocalledwheelmotors).
The primary requirements of the EREV motor are summarized as
follows:
❖High instant power and high power density.
❖High torque at low speeds for starting and climbing, and high power
at high speeds for cruising.
❖An extensive speed range including constant-torque and constant-
power regions. In this case, the APU, when it is on, needs to operate
in the same regions.
❖Fast torque response.
❖High efficiency over a large speed and torque ranges.
❖High reliability and robustness for various vehicle operating
conditions.
❖Reasonable cost.

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GM Chevy Volt

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HOW DOES AN EXTENDED-RANGE HYBRID WORK?
▪Whenthebatteryisdischargedtoaspecificlevel,the
combustionunitstartsup,therebyturningonthegenerator.
▪Itstaskistoprovideenergytotheelectricmotor,aswellas
chargethebattery.
▪Itbecomespossibletoincreaserange,whichcanbequitea
probleminotherelectricorhybridvehicles.
▪ThebiggestadvantageofEREVsisthat,despitethepresence
ofaninternalcombustionengine,theyarealmostas
environmentallyfriendlyandenergy-efficientasBEVs.
▪Theinternalcombustionunitisusedonlytokeepthe
batterychargedandnottodirectlypropelthevehicle.
E-REVs’electric-onlyrangevariesbuttypicallyitwillbemorethan40miles—theBMWi3Range
Extendercanmanagearound50-80milesbeforeneedingpetrolassistance,foratotalrange
betweenstopsof160to186miles.

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Blended PHEVs
▪BlendedPHEVshavebecomemorepopularbecauseofthereducedsystem
cost(smallerelectricmotor,smallerbatterypack,andlowerbatterypower
ratings),aswellastheflexibilityofoptimizingfueleconomyfordifferent
drivingconditions.
▪ComparedtoanEREV,ablendedPHEVusuallyusesaparallelorcomplex
configurationinwhichtheengineandthemotorcanbothdrivethewheels
directly.
▪Sincetheengineisavailableforpropulsionathighpowerdemand,thesize
oftheelectricmotorandthepowerrequirementforthebatterypackcanbe
muchsmallerthantheoneinanEREV.
▪Therefore,thecostofthevehicleisreduced.Planetarygear-basedhybrid
vehicles,suchastheToyotaPrius,andtheGMtwo-modehybrid,canbe
consideredasparallelconfigurationssincetheelectricmotorisinparallel
withtheengineoutput,whilethegeneratorisusedtorealizethe
continuouslyvariabletransmission(CVT)andtooptimizeengineoperation.

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Why PHEV?
▪Asurveyshowedthat78%oftheUSpopulationdrivesanaverage
of40miles(64km)orlessintheirdailycommuting.Figureshows
thedistributionofdailymilesdrivenversuspercentageof
population.
▪Basedonthissurvey,aPHEVwithanelectricrangeof40miles(or
PHEV40)willsatisfythedailydrivingneedsof78%oftheUS
populationwhiledrivingonelectricityintheirdailycommuting.
▪Furthermore,peopleowninga40mileelectricrangePHEVbut
drivinglessthan40milesdailywillnotneedtorefuelgasolineif
theychargetheircaratnightonadailybasis.PHEVscanproduce
significantenvironmentalandeconomicbenefitsforsociety.
▪TheadvantagesofPHEVscanbeevaluatedbyhowmuchfuelis
displaced,aswellasbyhowmuchpollution,includinggreenhouse
gas(GHG)emissions,canbereduced

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DatafromtheU.S.BureauofTransportationshowthat78%ofcommuterstravel40
milesorlesseachday-theexpectedbattery-onlyrangeofPHEVswithroutine
overnightcharging.Forlongerdistances,thevehiclescouldrunindefinitelyin
hybrid(gasoline/electric)mode.

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The main purpose for developing PHEVs can be summarized as follows:
1.Displacementoffossilfuelconsumptioninthetransportationsector:Since
PHEVownerswillnotneedtorefuelgasolineorneedlessgasoline,asignificant
amountoffossilfuelcanbesaved.Thiswillhavealong-termimpactonthe
economy,environment,andpoliticalarena.
2.Reductionofemissions:Duetothereduceduseofgasoline,asignificant
amountofemissionscanbereducedduetothelargedeploymentofPHEVs.
Centralizedgenerationofelectricityismuchmoreefficientandhasmuchless
emissionsthangasoline-poweredcars.Mitigationofemissionsfromurban(bycars)
toremoteareas(inpowerplants)whereelectricityisgeneratedcanalsomitigate
theheavypollutioninpopulation-densemetropolitanareas.Asmoreandmore
electricityinthefuturewillcomefromrenewableenergysources(whichwillbe
usedbyPHEVs),theemissionscanbefurtherreduced.
3.Energycostsavings:PHEVsuseelectricityfortheinitialdrivingrange.Since
electricityischeaperthangasolineonanequivalentenergycontentbasis,thecost
permiledrivenonelectricityischeaperthanongasoline.
4.Maintenancecostsavings:PHEVscangenerallysavemaintenancecosts.Due
totheextensiveuseofregenerativebraking,brakingsystemmaintenanceand
repairislessfrequent,suchasbrakepadreplacement,brakefluidchange,andso
on.Sincetheengineisnotoperating,oroperatingformuchlesstime,therewillbe
longerintervalsforoilchangesandotherenginemaintenanceservices.

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5.Backuppower:APHEVcanbeusedasabackuppowersourcewhena
bidirectionalchargerisprovided.AtypicalPHEVbatterypackcanprovideahome
orofficewith3–10kWofpowerforafewhours,andtheonboardengine
generator/motorcanfurtherextendthebackupdurationbyusinggasolineto
generateelectricity.
6.End-of-lifeuseofthebattery:Batteriesthatcannolongerprovidethe
desiredperformanceinaPHEVcanpotentiallybeusedforgridenergystorage,
whichprovidesvoltageregulation,systemstability,andfrequencyregulationfora
powergrid.Inparticular,frequencyregulationandstabilitybecomemoreand
moreimportantasmoreandmorerenewableenergygenerationisputonthe
powergrid.These“retired”batteries,whichmaystillhave30–50%oftheiroriginal
energycapacity,canprovidethistypeofservice.

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Equivalent Electric Range of Blended PHEVs
❑ForanEREV,theelectricrangecanbeeasilycalculated.
❑ForablendedPHEV,theremaybenopureelectricdriving
rangeavailableforsomedrivingcycles.
❑Tofindtheequivalentelectricrange,itisusefultocomparethe
fueleconomyofablendedmodePHEVduringcharge-
depletion(CD)modetothatofacomparableHEV.

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❖Theextended-rangeelectricvehicle(E-REV)iseffectivelyanall-electric
vehicle,withallthemotivepowerprovidedbyanelectricmotor,but
withasmallICEpresenttogenerateadditionalelectricpower.
Alternatively,itmaybeviewedasaserieshybridwithamuchlarger
battery,namely,10–20kWh.
❖Whenthebatteryisdischargedtoaspecifiedlevel,theICEisswitched
ontorunageneratorthat,inturn,suppliespowertotheelectricmotor
and/orrechargesthebattery.Withthisarrangement,therange
limitationthatisinherentinaBEVcanbeovercome.
❖Formoderatedistances,E-REVscanoperateinfull-electricmodeand
arethenascleanandenergy-efficientasBEVs(unlikeparallelhybrids
andotherserieshybridswiththeirsmallerbatteriesandverylimited
electricrange).

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Forlongerdistances,E-REVsutilizetheICEtokeepthebatterycharged,but
consumenoticeablylessfuelthanconventionalICEVsforthefollowingtwo
reasons:
(i)TheengineofanE-REVissignificantlysmallerthanthatofaconventional
ICEV–itonlyneedstomeetaveragepowerdemandsbecausepeakpoweris
deliveredbythebatterypack.TheengineofanICEV,ontheotherhand,must
alsocoverpeak-powersurges,e.g.accelerations.
(ii)TheengineofanE-REVoperatesataconstant,highlyefficient,rotation
speed;whereasthatofanICEVoftenrunsatloworhighrotationspeeds
duringwhich,inbothsituations,itsefficiencyislow.
ThedifferentmodesofE-REVoperationareshownschematicallyinFigure.
ThevehiclebeginsitsjourneywiththebatterySoCcloseto100%.Allthe
vehiclepowerisprovidedbytheelectricmotor,whichdrawsenergyonlyfrom
thebattery,andtherearenolocalexhaustemissions.Thebatteryispartly
rechargedwitheachregenerativebrakingevent.Whenthebatteryisdepleted
toapre-ordainedSoC–markedinFigure5atthreelevelsofincreasing
severity,viz.,green,orangeandred–thevehicleswitchestoextended-range
mode

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WhilethevehicleisoperatinginthismodetheICEisswitchedonasand
whennecessarytokeepthebatterywithintheSoCrangemarkedbythe
greenandreddashedlines.Afterthejourney,thebatterySoCisreturnedto
100%withpowertakenfromthegrid.Afuturepossibilitywouldbeto
replacethepistonenginewithamicrogas-turbineastherangeextender.
JaguarhasproducedtheC-X75hybridconceptcar,whichisanE-REVwith
twosmallgasturbines(each35kg)tochargethebattery(15-kWhlithium-
ion).Four145-kWelectricmotors,oneateachofthewheels,candrivethe
1350-kgvehicleupto205mph(330kmh−1)withatotaltorqueof1600N
m.TheC-X75hasanelectric-onlyrangeof70miles(113km),anda60-Lfuel
tank.

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Fuel Economy of PHEVs
Thefueleconomyofconventionalvehiclesisevaluatedbyfuelconsumption
(liters)per100km,ormilespergallon.IntheUnitedStates,theEnvironmental
ProtectionAgencysetsthemethodsforfueleconomycertification.Thereare
usuallytwonumbers,oneforcitydrivingandoneforhighwaydriving.Thereisan
additionalfueleconomynumberthatevaluatesthecombinedfueleconomyby
combiningthe55%cityand45%highwayMPGnumbers
ForpureEVs,thefueleconomyisbestdescribedbyelectricityconsumptionfora
certainrange,forexample,watthour/mileorkWh/100km.Forexample,atypical
passengercarconsumes120–250Wh/mile.

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Therefore,apassengercarthatconsumes240Wh/milewillhavean
equivalentgasolinemileageof140MPGfromtheenergypointofview.
InordertocomparethefuelefficiencyofEVswithconventionalgasolineor
dieselvehicles,theenergycontentofgasolineisusedtoconvertthe
numbers.Since1gallonofgasolinecontains33.7kWhenergy,the
equivalentfueleconomyofanEVcanbeexpressedas
1.Well-to-Wheel Efficiency
2.PHEV Fuel Economy
3.Utility Factor

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Well-to-Wheel Efficiency
Theabovefuelefficienciesarealsocalledtank-to-wheelefficiencies.Thisdoes
notreflectthelossesduringtherefininganddistribution.Itissometimeseasier
tocomparetheoverallfuelefficienciesofconventionalvehiclesandEVs.For
gasoline,thisefficiencyis83%,whichreflectsalumpedefficiencyfromthe
refininganddistributionofgasoline.Forelectricitygeneration,thisefficiencyis
30.3%,whichreflectsalumpedefficiencythatincludeselectricitygenerationof
32.8%(assumeelectricityisgeneratedfromgasoline)anddistributionof
electricityat92.4%.Chargeefficiencyofthebatteryalsoneedstobereflected

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Fuel economy labelingfor all-electric-capable PHEV
Fuel economy labelingfor blended PHEV
PHEV Fuel Economy

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ForPHEVs,itisusuallyconfusingastowhichnumbershouldbe
used.Here,wediscusstwodifferentscenarios:all-electric
capablePHEVsandblendedPHEVs.
Forall-electriccapablePHEVs,itisusefultoindicatetheelectric
range,inmilesorkilometers,andassociatedenergyconsumption
duringthatrange,inkilowatthours/mile,andpotentiallygas
equivalentMPG.Anothersetofnumbersisneededtoshowthe
MPGduringCSmodedriving.Asuggestedlabelisshownin
Figure1.
ForblendedPHEVs,sincethereisnopureelectricdrivingrange,
itisusefultolabelthefueleconomyinCDandCSmode
separatelyasshowninFigure2.Itmaybepreferredtoinclude
theelectricenergyconsumptionduringCDmodeaswell.

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Utility Factor
Anotherapproachforfueleconomyclarificationistouseautility
factor.AutilityfactorisdefinedastheratioofCDrangeofa
PHEVtothetotaldistancesdrivenindailycommutingbyallthe
USpopulation.Forexample,aCDrangeof20mileswillresultin
autilityfactorof40%(Figure).Usingtheutilityfactor,the
combinedfueleconomycanbeexpressedas
where UF is the utility factor, and FECD and FECS are the fuel
economy during CD and CS operation of a PHEV, respectively.

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Definition of utility factor of PHEV (VMT, Vehicle Miles Traveled.)

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Power Management of PHEVs
▪APHEVinvolvestheoperatingconditionsofbothCharge-Depletion
(CD)modeandCharge-Sustaining(CS)mode.
▪Typically,whenthebatteryisfullycharged,thevehicleisoperatedin
CDmode,andwhenthebatterystateofcharge(SOC)reachesalow
threshold,itswitchestoCSmode.
▪InCDmode,thevehiclewillmaximizetheuseofbatteryenergy.
▪InCSmodethevehiclewillusegasolinetopowerthevehiclewhile
maintainingthebatterySOCatthesamelevel.
▪DuringCDmodeoperation,thegoalofvehiclepowermanagementis
tominimizethetotalenergyconsumptionbydistributingpower
betweenthebatteryandthegasolineengine/generatorforagiven
drivingscenario.
▪Inotherwords,thegoalofpowermanagementinaPHEVisto
minimizethefuelconsumptionforagivendrivescenario.

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ForaseriesPHEV(orEREV),ifthedrivedistanceislessthanthe
nominalelectricdriverange,thenitispossibletooperatethe
vehicleinall-electricmode,hencenofuelisconsumed.Ifthedrive
distanceislongerthantheelectricrange,thentherearethree
possibleapproachesforoperatingthevehicle:
Operatethevehicleinelectricmodeuntilthebatteryisdepletedto
apresetthreshold,thenruninCSmode.
2.Operatethevehicleinablendedmodewiththeengineturning
onathighpowerdemands,anddepletethebatterytothepreset
thresholdattheendofthetotaldrivingcycle.
3.Operatethevehicleinablendedmodewiththeengineturning
onathighpowerdemandsbutwithanoptimalbatterydischarge
policy,sothebatterywillbedepletedtothepresetthreshold
beforetheendofthetotaldrivingcycle.

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Intheseapproaches,sincethetotaldrivedistanceisthesame,the
onethatconsumestheleastfuelwillbethebestchoice.Thefact
thatthebatterywillexhibitalargepowerlossathighpoweroutput
incomparisontoitsoutputpower,itmaybeadvantageousto
operatethevehicleinblendedmode.
Theoptimizationproblemcanbeexpressedas
min{fuelconsumption}
Subjecttoagivendistanceanddrivecycle
ForablendedPHEV,sincethereisnopureelectricrangeavailable,
thegoalofthepowermanagementistominimizefuelconsumption
foragivendrivecycleandgiventotalbatteryenergyavailable.This
isstronglyrelatedtothecharacteristicsofthepowersources
(batteryandengine).

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FigureshowsanidealizedblendedPHEVmodelforstudying
powermanagement.Inthismodel,themechanicalcouplingand
transmissionlossesareconsideredaspartofthecalculated
vehiclepower.

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End-of-life Battery For Electric Power Grid Support
▪Ingeneral,batteryenergycapacitytendstofadeovertime
andoverdischargecycles.
▪Typicalbatteryenergycapacityasafunctionoftimeis
showninFigure.
▪With70%SOCdepletion,alithium-ionbatterycantypically
last3000–4000chargecycles.
▪Thisisapproximately10yearsforaPHEV.Atthattime,the
batterycapacitymaybeonly50%ofitsinitialcapacity.
▪Whilethisisnotsatisfactoryforthecarownerduetothe
reducedelectricdrivingrange,thebatteryitselfmaybeused
forotherpurposes,suchasforelectricgridsupport.

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Sincethereislessspace/weightconstraintsforpowergrid
applications,thesebatteriescanbeusedforgridenergy
storageforpeakshaving,frequencyregulation,andstability
control.
Whenmoreandmorerenewableenergyisconnectedtothe
electricpowergrid,stabilityofthegridbecomesextremely
importantduetotheintermittentnatureofrenewableenergy
generation.
Figure: Typical battery capacity versus cycle life

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BidirectionalChargerisanadvancedEVchargercapableoftwo-way
charging;thismightsoundrelativelysimple,butit’sacomplexpower
conversionprocessfromAC(alternatingcurrent)toDC(directcurrent),as
opposedtoregularunidirectionalEVchargersthatchargeusingAC.

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UnlikestandardEVchargers,bidirectionalchargersoperatemuchlikean
inverterandconvertACtoDCduringchargingandthereverseduring
discharging.However,bidirectionalchargerscanonlyworkwithvehicles
thatarecompatiblewithtwo-wayDCcharging.Unfortunately,thereis
currentlyaverysmallnumberofEVswhicharecapableofbidirectional
charging,themostwell-knownbeingthelatermodelNissanLeaf.Dueto
bidirectionalchargersbeingfarmoresophisticated,theyarealsomuch
moreexpensivethanregularEVchargerssincetheyincorporateadvanced
powerconversionelectronicstomanagetheenergyflowtoandfromthe
vehicle.
Tosupplypowertoahome,bidirectionalchargersalsoincorporate
equipmenttomanagetheloadsandisolatethehousefromthegridduring
anoutage,knownasislanding.Thebasicoperatingprincipleofa
bidirectionalEVchargerisverysimilartobidirectionalinverter-chargers,
whichhavebeenusedforbackuppowerinhomebatterystoragesystems
foroveradecade.

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Bidirectionalchargerstandards-Thisisabrieftechnicalsummaryofthe
currentbidirectionalchargerstandard.Thelateststandardfor
communicationbetweenanEVandabidirectionalchargerisISO
15118:2014-Roadvehicles-Vehicle-to-GridCommunicationInterface.
Thepurposeofthisstandardistodetailthecommunicationbetweenan
EV(BEVoraPHEV)andtheEVSE(ElectricVehicleSupply
Equipment),morecommonlyknownasanEVcharger.SeetheV2G
sectionbelowfordetailsonthevehicle-to-gridstandards

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Uses of Bidirectional Charging
Bidirectionalchargerscanbeusedfortwodifferentapplications.Thefirst
andmosttalkedaboutisVehicle-to-gridorV2G,designedtosendor
exportenergyintotheelectricitygridwhenthedemandishigh.If
thousandsofvehicleswithV2Gtechnologyarepluggedinandenabled,
thishasthepotentialtotransformhowelectricityisstoredandgenerated
onamassivescale.EVshavelarge,powerfulbatteries,sothecombined
powerofthousandsofvehicleswithV2Gcouldbeenormous.NoteV2Xis
atermthatissometimesusedtodescribeallthreevariationsdescribed
below.
▪Vehicle-to-gridorV2G-EVexportsenergytosupporttheelectricity
grid.
▪Vehicle-to-homeorV2H-EVenergyisusedtopowerahomeor
business.
▪Vehicle-to-loadorV2L*-EVcanbeusedtopowerappliancesor
chargeotherEVs
*V2Ldoesnotrequireabidirectionalchargertooperate

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TheseconduseofbidirectionalchargersisforVehicle-to-homeorV2H.
Asthenamessuggest,V2HenablesanEVtobeusedmuchlikeahome
batterysystemtostoreexcesssolarenergyandpoweryourhome.For
example,atypicalhomebatterysystem,suchastheTeslaPowerwall,has
acapacityof13.5kWh,whileanaverageEVhasacapacityof65kWh,
whichisequivalenttoalmostfiveTeslaPowerwalls.Duetothelarge
batterycapacity,afullychargedEVcouldsupportanaveragehomefor
severalconsecutivedaysormuchlongerwhencombinedwithrooftop
solar.

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Vehicle-to-Grid (V2G) Technology

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Vehicle-to-grid(V2G)iswhereasmallportionofthestoredEVbatteryenergyis
exportedtotheelectricitygridwhenneeded,dependingontheservicearrangement.To
participateinV2Gprograms,abidirectionalDCchargerandacompatibleEVisrequired.
Ofcourse,therearesomefinancialincentivestodothisandEVownersaregivencreditsor
reducedelectricitycosts.EVswithV2Gcanalsoenabletheownertoparticipateinavirtual
powerplant(VPP)programtoimprovegridstabilityandsupplypowerduringpeak
demandperiods.OnlyahandfulofEVscurrentlyhaveV2GandbidirectionalDCcharging
capability;theseincludethelatermodelNissanLeaf(ZE1)andtheMitsubishiOutlanderor
Eclipseplug-inhybrids.
Despitethepublicity,oneoftheproblemswiththeroll-outofV2Gtechnologyisthe
regulatorychallengesandlackofstandardbidirectionalchargingprotocolsandconnectors.
Bidirectionalchargers,likesolarinverters,areconsideredanotherformofpower
generationandmustmeetallregulatorysafetyandshutdownstandardsintheeventofa
gridfailure.Toovercomethesecomplexities,somevehiclemanufacturers,suchasFord,
havedevelopedsimpleACbidirectionalchargingsystemsthatonlyoperatewithFordEVs
tosupplypowertothehomeratherthanexportingtothegrid.Others,suchasNissan,
operateusinguniversalbidirectionalchargerssuchastheWallboxQuasar.
Vehicle-to-grid(V2G)standardsaredifficultandcomplexastheyinvolveregulatingthe
power,safetyandelectricalrequirementswhendischargingenergyintothegrid.

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Advantages of V2G
1.Improvingsecurity:V2Ginverterscanrespondquicklytocontroltheeffects
ofanydisturbanceascomparedtotheturbo-generatorgovernor.Thiswillhelp
thepowersystemtobemorerobustandreducethevulnerability.
2.Improvingreliability:TheadvantageoflocatingtheV2Gsystemanywherein
thedistributionsystemmakesthebackupsupplyavailableataclosedistance
eventhoughitmaynotbeinstalledattheconsumer’slocation.Thiswillhavea
majorimpactonconsumerreliabilityasmostinterruptionsaredueto
disturbancesinthedistributionnetworks.
3.Impactongeneration:ByconnectingalargenumberofPHEVsorV2G
systemsduringdaytimethepeakpowercanbecurtailedduringthedailypeak
loadperiod.Also,duringthelight-loadperiodPHEVscanbeconnectedtocharge
thebatterysystem,thusallowingthebaseloadgeneratorstooperateefficiently
withouttheneedtocarrylargeamountsofspinningreserve.
4.Environmentaladvantage:UsingPHEVscanreduceenvironmental
pollution.Theycanpromotethereductionofgreenhousegasemissionsby
indirectlyusingcleanelectricityastransportationfuel.

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▪Vehicle-to-grid,orV2G,isaconceptreferringtothecapabilityof
bidirectionalpowerandenergyexchangebetweenthepowergridand
thevehiclebattery.
▪Withthebidirectionalcharger,thevehiclecanbeusedapowerbackup
forthehomeoroffice.
▪ItisalsopossibletousethePHEVbatterytocontrolthestabilityand
regulatethefrequencyandvoltageofthepowergrid,suchasina
distributedpowergridandwithrenewableenergygeneration.
▪PHEVsneedtobechargedfromtheelectricpowergrid.During
charging,thechargerwillgenerateinrushcurrent,harmonics,andcould
causethegridtomalfunctionifnotcoordinatedproperly.
▪Inabroadsense,andintheforeseeablefuture,hundredsofthousandsof
PHEVswillbeconnectedtothepowergridaselectricdrive
transportationprevailsasourultimatesolutiontobecomingindependent
offossilfuels.
▪Itisimperativetostudythegrid-tovehicle(G2V)impactonpower
systemoperationandtoconsidervariousfactorssuchasbatterysize,
charging,PHEVdistribution,andefficiency.

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▪InordertooptimizeG2Vitisimportanttoeducateconsumersinthe
contextofa“smartgrid.”
▪Theyshouldbemadeawareofthefactthatbatterychargingatnight
wouldimproveutilitygenerationefficiency,becauseatnight-timethe
electricityissuppliedbythebaseloadgenerationunits.
▪Studiesshowthatevenwith50%penetrationofPHEVsintothepower
system,noadditionalgeneratingcapacityornonewpowerplantsare
required.
▪AlthoughthereareconcernswithPHEVsstrainingthegrid,PHEVs,if
properlymanaged,actuallycouldhelppreventbrownouts,reducethe
costofelectricityandaccommodatetheintegrationofmorerenewable
energyresources

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71. 71
PHEV Battery Charging

72. 72
Chargingyourall-electricvehicle(EV)orplug-inhybridelectricvehicle
(PHEV)–togetherknownasplug-inelectricvehicles(PEVs)–issimilarto
chargingyourotherelectronics.Oneendofanelectricalcordisplugged
intoyourcar,andtheotherendispluggedintoapowersourceorcharging
equipment.
Therearethreecategoriesofchargingequipmentbasedonhowquickly
eachcanrechargeacar’sbattery.
ChargingtimesforPEVsarealsoaffectedby:
▪Howmuchthebatteryisdepleted
▪Howmuchenergythebatterycanstore
▪Thetypeofbattery
▪Temperature
Level1chargingusesastandard120wallplugwhileLevel2utilizesa220-
voltoutlet.Manyplug-inhybridownershavealocalelectricalplumbanew
220-voltlineintheirgaragetospeedupchargingtimes.

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Charger Types and Speeds
EVscanbechargedusingelectricvehicleserviceequipment(EVSE)operatingat
differentchargingspeeds.
Level1:Level1equipmentprovideschargingthroughacommonresidential120-
volt(120V)ACoutlet.Level1chargerscantake40-50+hourstochargeaBEVto
80percentfromemptyand5-6hoursforaPHEV.
Level2:Level2equipmentoffershigher-rateACchargingthrough240V(in
residentialapplications)or208V(incommercialapplications)electricalservice,
andiscommonforhome,workplace,andpubliccharging.Level2chargerscan
chargeaBEVto80percentfromemptyin4-10hoursandaPHEVin1-2hours.
DirectCurrentFastCharging(DCFC)
Directcurrentfastcharging(DCFC)equipmentoffersrapidchargingalongheavy-
trafficcorridorsatinstalledstations.DCFCequipmentcanchargeaBEVto80
percentinjust20minutesto1hour.MostPHEVscurrentlyonthemarketdonot
workwithfastchargers.
Level2andDCFCequipmenthasbeendeployedatvariouspubliclocations
including,forexample,atgrocerystores,theaters,orcoffeeshops.Whenselectinga
chargertype,consideritsvoltages,resultingchargingandvehicledwelltimes,and
estimatedup-frontandongoingcosts.

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▪TherearethreelevelsofchargingforthePHEVdependingonthe
voltage:single-phaseAC120V,single-phaseAC240V,andthree-
phaseAC480V.Thedifferentvoltagelevelswillaffectthecharging
time,rangingfromhourstotensofminutes.Ingeneral,therearefour
typesofchargingalgorithmsforPHEV:constantvoltage,constant
current,constantvoltageandconstantcurrent,andpulsecharging.
▪ThePHEVsconnectedtothedistributionsystemviaasingle-phase
transformerarechargedbythepulsechargingtechnique.Initiallythe
batteryisassumedtohavea90%SOC.Thebatteryischargedbythe
DC–DCconverterwithpulsecurrentuntilitreachesa95%SOC.
▪TheAC–DCconverterconnectedtothedistributionsystemdrawsunity
powerfactor,whichshowsthatthePHEVisutilityfriendly.

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