IEEE_-_Z_Source_Inverter

504IEEETRANSACTIONSONINDUSTRYAPPLICATIONS,VOL.39,NO.2,MARCH/APRIL2003Z-SourceInverterFangZhengPeng,SeniorMember,IEEEAbstract—Thispaperpresentsanimpedance-source(orimpedance-fed)powerconverter(abbreviatedasZ-sourcecon-verter)anditscontrolmethodforimplementingdc-to-ac,ac-to-dc,ac-to-ac,anddc-to-dcpowerconversion.TheZ-sourceconverteremploysauniqueimpedancenetwork(orcircuit)tocoupletheconvertermaincircuittothepowersource,thusprovidinguniquefeaturesthatcannotbeobtainedinthetraditionalvoltage-source(orvoltage-fed)andcurrent-source(orcurrent-fed)converterswhereacapacitorandinductorareused,respectively.TheZ-sourceconverterovercomestheconceptualandtheoreticalbarriersandlimitationsofthetraditionalvoltage-sourceconverter(abbreviatedasV-sourceconverter)andcurrent-sourceconverter(abbreviatedasI-sourceconverter)andprovidesanovelpowerconversionconcept.TheZ-sourceconceptcanbeappliedtoalldc-to-ac,ac-to-dc,ac-to-ac,anddc-to-dcpowerconversion.Todescribetheoperatingprincipleandcontrol,thispaperfocusesonanexample:aZ-sourceinverterfordc-acpowerconversionneededinfuelcellapplications.Simulationandexperimentalresultswillbepresentedtodemonstratethenewfeatures.IndexTerms—Converter,current-sourceinverter,inverter,voltage-sourceinverter,Z-Sourceinverter.I.INTRODUCTIONTHEREEXISTtwotraditionalconverters:voltage-source(orvoltage-fed)andcurrent-source(orcurrent-fed)con-verters(orinvertersdependingonpowerflowdirections).Fig.1showsthetraditionalthree-phasevoltage-sourceconverter(ab-breviatedasV-sourceconverter)structure.Adcvoltagesourcesupportedbyarelativelylargecapacitorfeedsthemaincon-vertercircuit,athree-phasebridge.Thedcvoltagesourcecanbeabattery,fuel-cellstack,dioderectifier,and/orcapacitor.Sixswitchesareusedinthemaincircuit;eachistraditionallycom-posedofapowertransistorandanantiparallel(orfreewheeling)diodetoprovidebidirectionalcurrentflowandunidirectionalvoltageblockingcapability.TheV-sourceconverteriswidelyused.It,however,hasthefollowingconceptualandtheoreticalbarriersandlimitations.•Theacoutputvoltageislimitedbelowandcannotex-ceedthedc-railvoltageorthedc-railvoltagehastobegreaterthantheacinputvoltage.Therefore,theV-sourceinverterisabuck(step-down)inverterfordc-to-acpowerconversionandtheV-sourceconverterisaboost(step-up)rectifier(orboostconverter)forac-to-dcpowerconver-PaperIPCSD02–078,presentedatthe2002IndustryApplicationsSocietyAnnualMeeting,Pittsburgh,PA,October13–18,andapprovedforpublicationintheIEEETRANSACTIONSONINDUSTRYAPPLICATIONSbytheIndustrialPowerConverterCommitteeoftheIEEEIndustryApplicationsSociety.ManuscriptsubmittedforreviewJune1,2002andreleasedforpublicationDecember2,2002.TheauthoriswiththeDepartmentofElectricalandComputerEngineering,MichiganStateUniversity,EastLansing,MI48824-1226USA,andalsowiththeCollegeofElectricalEngineering,ZhejiangUniversity,Hangzhou310027,China(e-mail:[e-mail]).DigitalObjectIdentifier10.1109/TIA.2003.808920Fig.1.TraditionalV-sourceconverter.Fig.2.TraditionalI-sourceconverter.sion.Forapplicationswhereoverdriveisdesirableandtheavailabledcvoltageislimited,anadditionaldc-dcboostconverterisneededtoobtainadesiredacoutput.Thead-ditionalpowerconverterstageincreasessystemcostandlowersefficiency.•TheupperandlowerdevicesofeachphaselegcannotbegatedonsimultaneouslyeitherbypurposeorbyEMInoise.Otherwise,ashoot-throughwouldoccurandde-stroythedevices.Theshoot-throughproblembyelec-tromagneticinterference(EMI)noise’smisgating-onisamajorkillertotheconverter’sreliability.DeadtimetoblockbothupperandlowerdeviceshastobeprovidedintheV-sourceconverter,whichcauseswaveformdistor-tion,etc.•AnoutputLCfilterisneededforprovidingasinusoidalvoltagecomparedwiththecurrent-sourceinverter,whichcausesadditionalpowerlossandcontrolcomplexity.Fig.2showsthetraditionalthree-phasecurrent-sourceconverter(abbreviatedasI-sourceconverter)structure.Adccurrentsourcefeedsthemainconvertercircuit,athree-phasebridge.Thedccurrentsourcecanbearelativelylargedcinductorfedbyavoltagesourcesuchasabattery,fuel-cellstack,dioderectifier,orthyristorconverter.Sixswitchesare0093-9994/03$17.00©2003IEEEPENG:Z-SOURCEINVERTER505usedinthemaincircuit,eachistraditionallycomposedofasemiconductorswitchingdevicewithreverseblockcapabilitysuchasagate-turn-offthyristor(GTO)andSCRorapowertransistorwithaseriesdiodetoprovideunidirectionalcurrentflowandbidirectionalvoltageblocking.However,theI-sourceconverterhasthefollowingconceptualandtheoreticalbarriersandlimitations.•Theacoutputvoltagehastobegreaterthantheoriginaldcvoltagethatfeedsthedcinductororthedcvoltagepro-ducedisalwayssmallerthantheacinputvoltage.There-fore,theI-sourceinverterisaboostinverterfordc-to-acpowerconversionandtheI-sourceconverterisabuckrec-tifier(orbuckconverter)forac-to-dcpowerconversion.Forapplicationswhereawidevoltagerangeisdesirable,anadditionaldc–dcbuck(orboost)converterisneeded.Theadditionalpowerconversionstageincreasessystemcostandlowersefficiency.•Atleastoneoftheupperdevicesandoneofthelowerde-viceshavetobegatedonandmaintainedonatanytime.Otherwise,anopencircuitofthedcinductorwouldoccuranddest