A idirectional LLC Resonant Converter.docx

A idirectional LLC Resonant Converter.docx

《A idirectional LLC Resonant Converter.docx》由会员分享，可在线阅读，更多相关《A idirectional LLC Resonant Converter.docx（44页珍藏版）》请在冰点文库上搜索。

AidirectionalLLCResonantConverter

ABidirectionalLLCResonantConverterWithAutomaticForwardandBackwardModeTransition

TianyangJiang,JunmingZhang,SeniorMember,IEEE,XinkeWu,Member,IEEE,KuangSheng,SeniorMember,IEEE,andYoushengWang

Abstract—ThispaperproposesanimprovedbidirectionalLLCresonanttopologywithanewcontrolscheme.Alltheswitchesintheproposedtopologycanachievesoftswitching.Comparedwithtraditionalisolatedbidirectionaldc–dcconverterssuchasdualactivebridgeconverter,thereverseenergyandturn-offlossarereduceddramatically,andtheconversionefficiencycanbemuchimproved.Withtheproposednewcontrolscheme,thepowerflowdirectionandoutputpoweroftheproposedconvertercanbechangedautomaticallyandcontinuously,whichisattractiveforenergystoragesystemstobalancetheenergyandtokeepthedc-busvoltageconstant.Performanceoftheproposedcircuitisvalidatedbytheexperimentalresultsfroma1-kWprototype.Over97%efficiencyisachievedatfullloadconditionbasedontheprototype.

IndexTerms—Bidirectional,energystoragesystem（ESS）,highefficiency,LLC,resonantconverter.

I.INTRODUCTION

A

Senergysavingandenvironmentprotectionbecomemoreandmoreimportant,lotsofresearcheffortshavebeencar-

riedoutinordertoutilizetheenergyinacleanandefficientway.Therenewableenergyresources,suchasphotovoltaic（PV）andwindpower,arethemostpromisingwaysforcleanelectricpowergeneration.However,theintermittentnatureofthesere-sourcesintroducesissueslikesystemstability,reliability,andpowerquality.Energystoragesystems（ESSs）arerequiredtodealwithsuchintermittentoutagesforgrid-tiedandoffgridap-plications[1]–[3].Batteriesandsupercapacitorsarethemostpopularenergystoragecomponentsconsideringthepriceandperformance.Fig.1showsatypicaldistributedgeneration（DG）systemwithrenewableenergyresourcesandESSs.TheESSsshouldhavebidirectionalpowerflowcapabilitytostoretheexcessenergygeneratedbyrenewableresources,andreleaseitwhentherenewableenergyisnotsufficientorduringpeaktimesofenergyconsumption[4]–[6].So,thebidirectionaldc–dccon-verterisakeycomponentinESSstoenablethebidirectionalpowerflow.

ManuscriptreceivedOctober17,2013;revisedDecember31,2013;accepted

February6,2014.DateofpublicationFebruary20,2014;dateofcurrentver-sionOctober7,2014.ThisworkwassupportedbytheNationalNatureSci-enceFoundationofChinaunderGrants51277161,51007081,andtheNationalHighTechnologyResearchandDevelopmentProgramofChina863Program2011AA050402.RecommendedforpublicationbyAssociateEditorS.Choi.

TheauthorsarewiththeCollegeofElectricalEngineering,ZhejiangUniversity,Hangzhou310027,China（e-mail:

jiangtianyangtc@;zhangjm@;wuxinke@;shengk@;eewangys@）.

Colorversionsofoneormoreofthefiguresinthispaperareavailableonlineathttp:

//ieeexplore.ieee.org.

DigitalObjectIdentifier10.1109/TPEL.2014.2307329

Fig.1.TypicalDGsystemwithESSs.

Generally,bidirectionaldc–dcconvertersforESSsshouldhavehigh-powerdensity,highefficiency,andhighreliability.Variousbidirectionaldc–dctopologieshavebeenproposedandstudiedinthepastdecades[7]–[27].Forsafetyconsideration,thegalvanicisolationisusuallyrequired.Amongtheseisolatedtopologies,thedualactivebridge（DAB）converterhasattractedlotsofresearchinterestsduetoitssimplestructure,widerangesoftswitchingcapability,andhighefficiency[14]–[21].TheDABconverterhastwobridgetypeswitchesineachsideofthetransformer,andthephaseshiftanglebetweentheprimarysideswitchesandthesecondarysideswitchesdeterminesthepowerflowdirectionanditsoutputpower[14],[15].However,itsuffersfromhighreverseenergyandhighturn-offpowerlosswhichdeterioratetheoverallefficiency[21]–[25].Alotofmethodshavebeenproposedtofurtherimproveitsefficiencyandperformance.AnimprovedDABtopologywithreducedreverseenergyandsimplecontrolschemewasproposedin[21],butthetopologylostthebidirectionalpowerflowcapability.Severalcontrolmethodswithtwoormorephaseshiftanglesascontrolvariableswereproposedtominimizethereverseenergyin[22]–[25],butthecontrolmethodswerealittlebitcomplexandtheturn-offlosswasstillhigh.

Theturn-offpowerlossisrelatedtotheturn-offcurrent,whichcanbereducedbyoperatingtheDABtopologyinres-onantmodewithanextraresonantcapacitor,i.e.,dualbridgeseriesresonantconverter[26],[27].However,itcanonlyoper-ateunderbuckmodewhichisnotsuitableforwideinput/outputrangeapplicationslikeESSs.AnewbidirectionalSRCforwidevoltagerangeapplicationwithclampedcapacitorwasstudiedin[28],butthetopologyitselfiscomplexduetothecomplexauxiliarycircuits.

0885-8993©2014IEEE.Personaluseispermitted,butrepublication/redistributionrequiresIEEEpermission.

Seehttp:

//www.ieee.org/publicationsstandards/publications/rights/index.htmlformoreinformation.

Fig.2.ProposedbidirectionalLLCresonantconverter.

Amongtheresonantconverters,theLLCresonantconverterhassuperiorperformancecomparedtotheseriesresonantcon-verter（SRC）,especiallyforbuck/boostoperationcapability,narrowswitchingfrequencyvariationrange,andhighereffi-ciency[29]–[32].MostoftheresearchesonLLCresonantcon-verterarefocusedonunidirectionaldc–dcapplications,andverylittleresearchworkonbidirectionalLLCresonantconverterwasreportedintheliterature.AbidirectionalLLCresonanttopologyforvehicularapplicationswasproposedin[33].ThetopologywasstillatraditionalSRCduringbackwardoperation,whichisnotpreferredforwidevoltagerangeapplication.In[34],abidi-rectionalCLLCresonantconverterwithtworesonanttanksinthetransformerprimarysideandsecondaryside,respectively,wasproposed.Theextraresonanttankincreasedboththecostandvolumeoftheconverter,andthevoltagegainwasreducedcomparedwiththetraditionalLLCconverter.Furthermore,itusesthedead-bandcontrolandtheoutputvoltagecannotbe

achieveZVSforMOSFETsintheprimaryside.ForG<1,theresonantinductorLr,resonantcapacitorCrandtransformermagnetizinginductorLm1formtheLLCresonanttank,andtheauxiliaryinductorLm2isusedtohelptoachieveZVSforsecondarysideswitches.IfLm2（referredtotheprimaryside）isequaltoLm1,theparametersofresonanttankareexactlythesame,andtheconverterissymmetrical,whichmeanstheoperationisalsothesame.

Thecontrolschemeisveryimportanttoachievethedesiredcharacteristicsoftheproposedtopology.Themoststraightfor-wardcontrolschemeisturningONandOFFtheprimarysideswitchesandsecondarysideswitcheswithsameswitchingfre-quency[35].ThediagonalswitchesM1/M4andM2/M3intheinputbridgeareswitchingwith50%dutycycleandcomple-mentarilywithoutconsideringthedeadtime.ThegatedrivesignalsforM5/M8andM6/M7intheoutputbridgearethesameasthoseforM1/M4andM2/M3,respectively,whichcanberegardedasthesynchronouscontrol.Theswitchingfre-quencyisusedtocontroloutputpowerastraditionalLLCreso-nantconverter.Thus,thehighconductionlossandpoorreverserecoveryproblemofMOSFETbodydiodesintheoutputsidecanbeavoided.Andthecurrentintheoutputsideisalwaysincontinuousconductionmode（CCM）evenwhentheswitchingfrequencyisbelowtheresonantfrequency,whichisdifferentfromtraditionalunidirectionalLLCconverter.Moreover,theoutputcharacteristicsuchasvoltagegainisalsodifferent.

ThevoltagegainoftraditionalunidirectionalLLCresonantconverterwithdioderectifierintheouputsideisgivenin

（1）[36]

regulatedcontinuously.Andthecurrentintheoutputsidehasto

1

G=

（1）

flowthroughthebodydiodesoftheswitcheswhichmaycause

/[1+1

12212

highconductionloss.

k（1−x2）]

+Q（x−x）

ThispaperproposesanewbidirectionalLLCresonantcon-verterwithanewcontrolschemeforESSsapplications.ThecircuitdiagramisshowninFig.2.Thedetailedoperatingprin-cipleispresentedinSectionII.ThetheoreticalanalysisoftheproposedtopologyisgiveninSectionIII.SectionIVpresentstheexperimentalresultsfroma1-kWprototypewith75V–130Vinputand400-Voutput.

II.PRINCIPLEOFOPERATION

TheproposedbidirectionalLLCresonantconverterisshowninFig.2.Theenergystorageelementisinthetransformerpri-marysideandthedcbusisinthesecondaryside.Forbidirec-tionalpowerflow,twoactivebridgesareadoptedintheproposedtopology.Itshouldbenotedthatahalf-bridgestructurecanalsobeused.AnextrainductorLm2isaddedbetweenpointCandpointD.

Inthispaper,theforwardmodemeansthebatterydeliversenergytothedcbus,whichisadischargingmode.Andthebackwardmodeisachargingmode.ThevoltagegainGistheratioofdc-busvoltagereferredtotheprimarysidetothebattery

wherek=Lm2/Lristheinductanceratio,Zr=、Lr/Cristhecharacteristicimpedance,fr=1/2π√Lr·Cristhereso-

nantfrequency,fsistheswitchingfrequency,x=fs/fristhenormalizedswitchingfrequency,Roistheequivalentdc-loadresistance,andQ=π2Zr/8n2Roisthequalityfactor.

ThevoltagegainoftheproposedbidirectionalLLCconverterwiththesynchronouscontrolmethodisgivenin

（2）[35].TheoutputcurrentisalwaysinCCMwiththesynchronouscon-trolmethodwhenfs