Boost converter based power factor correction

Electric vehicles power factor correction

1. EE3028 -Design of Electric
Vehicle Charging System
Dr. C. PONMANI
Professor (CAS) & HOD i/c
Department of Electrical and Electronics Engineering
Government College of Engineering
Bodinayakkanur

2. Power Factor Correction in Charging System
NeedforPowerFactorCorrection
BoostConverterforPowerfactorCorrection
SizingtheBoostinductor
AverageCurrentsintheRectifier
CalculationofPowerLosses

3. NeedforPowerfactorcorrection:
Thepowerwegetfromgridis220V/415Vand50Hz.Butmostofthepowerdevicesrequireadifferentinput
fromwhatwegetfromgrid,sowehavetomakesomeconversionofthevoltageandcurrent.Switching
devicesarewidelyusedindifferentpowerconversiondevices.
Theintroducingofswitchingdevicesimprovedthedevices’efficiencyofpowerconversionbutbrought
problemslikeharmonicpollutionandlowpowerfactor.
Inordertoeliminateharmonicandimprovepowerfactor,peoplebringanewtechnologywhichiscalled
powerfactorcorrection.Becausepeoplenowaretryingtogethighqualitypower,powerfactorcorrectionis
inleadingedgeofpowerelectronicsresearch.Powerfactorcorrectionisveryimportantbecauselowpower
factorbringslotsofproblemstoourcircuitsandpowerdevices.Thekeypointtoimprovethepowerfactor
ofpowerdevicesistheresearchoftopologystructureofpowerfactorcorrectioncircuitandintegratedcircuit
ofpowerfactorcorrection.
Withthehighmodernizationandelectrificationofindustry,peoplenowhaveahigherrequirement
forthepowerquality.Badpowerqualitymaycausetheelectronicdevicesnotworkingproperlyorevennot
working.Forpowerquality,powerfactorisasignificantfactor,whichimpactspowerqualitydirectly.Small
powerfactorwillcausemanynegativeeffects,suchaspowergridwaveformdistortionandlargelineloss,
whichmayreducetheservicetimeofpowerdevices.

4. Nowadays,withenvironmentalproblemsandenergycrisisgettingincreasinglyserious,electricvehiclehasbecomeahot
topicbecauseofitsfeaturesoflownoise,zeroemissionsandsignificantadvantagesinenergyefficient.Assupporting
chargingequipmentforelectricvehicles,theresearchforon-boardchargerhasimportantsignificance.Moreover,asa
kindofenvironmentallyfriendlytransportation,theonboardchargerforelectricvehiclesshouldbeenvironmentally
friendlytoo.Especiallywhenalargenumberofenergystoragebatteriesconnectedtothegridascapacitiveload,itwill
inevitablyreducethepowerfactorofpowergrid,causingharmonicpollutionandlowefficiency.
So,withtheincreasinglywidespreaduseofelectricvehiclesinthefuture,thedevelopmentofpowerfactorcorrection
systemforon-boardchargerisveryimportant.
Methodsofpowerfactorcorrection:
Attheearlystage,peopleusedpassivenetworkthatwascomposedofcapacitorsandinductorstoachievepowerfactor
correction(PFC).However,thiskindofcircuithasthedisadvantagesoflargevolumeandlowperformanceinharmonic
suppressionofinputcurrent.
Later,withthedevelopmentofpowerelectronicstechnology,ActivePowerFactorCorrection(APFC)cameintobeing.
APFCtechnologyaddapowerconverterwithapowerfactorcorrectionfunctionbetweenrectifiercircuitandoutput
capacitanceinordertoensurethestabilityofoutputvoltageandcontroltheinputcurrentharmonicandphase
differencebetweeninputcurrentandvoltage.Moreover,becauseAPFCoperatesathighswitchingfrequency,APFC
technologyhasadvantageofsmallervolumeandpowerfactorandhighperformanceinefficiency.Theseadvantages
maketheAPFCtechnologyhavegraduallybecomethemainstreamofpowerfactorcorrectiondevelopment.

5. IntheEVchargingsystem,thefront-endAC-DCconverterisveryimportantandshouldmeetthe
requirementsoftheefficiencyandpowerdensity.TheAC/DCPFCboostconvertercomponentandits
controllerareshownintheblockdiagramofauniversalin-boardtwo-stagebatterycharger.
Simplifiedsystemblockdiagramofauniversalin-boardtwo-stagebatterycharger
BoostConverterforPowerfactorCorrection

6. BasicprincipleofPFC:
ThecircuitofAPFCcontainstwoparts,oneisthemaincircuitandtheotheristhecontrolcircuit.Wetake
boostPFCcircuitasanexample.Themaincircuitconsistsofasingle-phasebridgerectifierandDC-DC
converter.
Andforcontrolcircuit,wehavereferencevoltage(Vo,ref),voltageerroramplifier(VA),multiplier(M),current
erroramplifier(CA)andpulsewidthmodulator(PWM).
Aftercomparingtheoutputvoltagewiththereferencevoltage,theresultgoesthroughthevoltageerror
amplifier.Theoutputofvoltageerroramplifierandrectifiedinputvoltagetogethergotomultiplierandwe
settheoutputofthemultiplierasthereferenceofcurrentfeedbackcontrol.
Aftercomparingthereferencecurrentwiththeinputdetectedcurrent,theresultgoesintothecurrenterror
amplifierandcontroltheonandoffoftheswitchS.
Sowecanmaketheinputcurrentandtherectifierinputvoltagebeatalmostthesamephase,andthereis
lessharmoniccurrent,thatwecanincreasethepowerfactorandmaketheoutputvoltagestable.

7. Whenboostconverteristhemain
circuitofPFC,itcanonlyboostthe
voltagesothatthiscircuitisworking
stably.TheinductorLischargedwhen
switchSisonandwhenswitchSisoff,
Lisdischarged.
TheACinputcurrentisalwaysthe
samewithinductorcurrent,sothat
inputcurrentiscontinuous.When
implementinglargepowerDC-DC
convertingandpowerfactor
correction,thecontinuousinput
currenthasitsownadvantage.Atthe
sametime,theripplecurrentissmall
wheninputcurrentiscontinuous,soit
reducestheprocessingrequirements
forthefiltercircuit.Becausethesource
voltageoftheswitchisalways0,it’s
easytocontroltheswitch.

8. Hysteresiscurrentcontrol:
ThefollowingfigureshowsthehysteresiscurrentcontrolBoostPFCcircuit,thecontrolwaveformofswitchSandinductor
currentiLinhalfoftheswitchingcircle.Thevariablewetakecontrolinthiscontrolmodeistherangeoftheinductor
current.Wemultiplytheinputvoltagesignalwiththefeedbacksignaloftheoutputvoltage,thenwewillhavetwo
differentcurrentcontrolreferencesignalswhicharesamephaseandsamefrequencywiththeinputvoltage.Wecall
largersignalupperboundreferencecurrentloopsignalandthesmalleronelowerboundreferencecurrentloopsignal.
Wedetecttheinductorcurrentandcompareitwiththetworeferencecurrentsignals.
Thecontrolstrategyisasfollows:
WhentheswitchSison,theinductorLwillbecharged,andthedetectedinductorcurrentiscomparedwiththeupper
boundreferencecurrentloopsignal.Andwhentheinductorcurrentrisestotheupperbound,thetriggerlogiccontrol
willcutofftheswitchSandtheinductorstartsdischarging.
Whentheinductorcurrentfallstolowerbound,thetriggerlogiccontrolwillturnontheswitchandtheinductorLgets
charged.Inthiscontrolmode,theconductingtimeofswitchSisconstant,buttheshutdowntimevaries.Sotheswitching
cycleisnotconstant.Thebandwidthofhysteresisdecidesthesizeoftheripple,whichcanbeconstantorinproportionto
instantaneousaveragecurrent.
ForBoostPFC,hysteresiscurrentcontrolisasimplecontrolmode,becausewehavenoextramodulationsignal.Andwe
cangetwidecurrentbandwidthandfastdynamicresponse.Thedisadvantageofthiscircuitisveryobvious,thatis,the
loadhaslargeeffectsontheswitch,sowhenwedesignthefilterweneedtoconsiderthelowestswitchingfrequency.
Alsothehysteresisbandwidthhaslargeeffectonswitchingfrequencyandsystemperformance.Moreover,whensource
voltageapproacheszerothedifferencebetweentworeferencesignalsisverysmall,sowealwaysneedsome
compensationforthiscircuit.

9. Hysteresis
current
control PFC