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首页 UPS设计

UPS设计

UPS设计

UC
2014-02-19 0人阅读 举报 0 0 暂无简介

简介:本文档为《UPS设计pdf》,可适用于工程科技领域

IEEETRANSACTIONSONINDUSTRIALELECTRONICS,VOL,NO,AUGUSTControlofDistributedUninterruptiblePowerSupplySystemsJosepMGuerrero,SeniorMember,IEEE,LijunHang,andJavierUceda,Fellow,IEEEAbstractInthelastyears,theuseofdistributeduninterruptiblepowersupply(UPS)systemshasbeengrowingintothemarket,becominganalternativetolargeconventionalUPSsystemsInaddition,withtheincreasinginterestinrenewableenergyintegrationanddistributedgeneration,distributedUPSsystemscanbeasuitablesolutionforstorageenergyinmicrogridsThispaperdepictsthemostimportantcontrolschemesfortheparalleloperationofUPSsystemsActiveloadsharingtechniquesanddroopcontrolapproachesaredescribedTherecentimprovementsandvariantsofthesecontroltechniquesarepresentedIndexTermsDroopmethod,loadsharing,microgrids,parallelconnection,uninterruptiblepowersupply(UPS)IINTRODUCTIONDISTRIBUTEDgeneration(DG)isanemergingconcepttodecentralizethemanagementofelectricityproductionHowever,DGmakesnosensewithoutdistributedstorageenergysystemsThus,theparalleloperationisaspecialfeatureofhighperformanceuninterruptiblepowersupply(UPS)systems–TheparallelconnectionofUPSinvertersisachallengingproblemthatismorecomplexthanparallelingdcsources,sinceeveryinvertermustproperlysharetheloadwhilestayingsynchronizedIntheory,iftheoutputvoltageofeveryinverterhasthesameamplitude,frequency,andphase,thecurrentloadcouldequallybedistributedHowever,duetothephysicaldifferencesbetweentheinvertersandthelineimpedancemismatches,theloadwillnotproperlybesharedThisfactwillleadtoacirculatingcurrentamongtheinvertersthatcandamageoroverloadthemThefastdevelopmentofdigitalsignalprocessorshasbroughtaboutanincreaseincontroltechniquesfortheparalleloperationofUPSinvertersThesecontrolschemescanbeclassifiedintotwomaingroupswithregardtotheuseofcontrolwireinterconnectionsThefirstoneisbasedonactiveloadsharingtechniques,andthemajorpartofthemisderivedfromcontrolschemesofparallelconnecteddc–dcconverters,suchascentralized,,master–slave(MS)–,averageloadsharing(ALS)–,andcircularchaincontrol(C),Althoughthesecontrolschemesachievebothgoodoutputvoltageregulationandequalcurrentsharing,theyneedManuscriptreceivedFebruary,revisedApril,PublishedJuly,(projected)JMGuerreroiswiththeDepartmentofAutomaticControlandComputerEngineering,TechnicalUniversityofCatalonia,Barcelona,Spain(email:josepmguerreroupcedu)LHangiswiththeCollegeofElectricalEngineering,ZhejiangUniversity,Hangzhou,ChinaJUcedaiswiththeDivisióndeIngenieríaElectrónica,UniversidadPolitécnicadeMadrid,Madrid,SpainDigitalObjectIdentifierTIEcriticalintercommunicationlinesamongmodulesthatcouldreducethesystemreliabilityandexpandabilityThesecondkindofcontrolschemefortheparalleloperationofinvertersismainlybasedonthedroopmethod–ThistechniqueconsistsofadjustingtheoutputvoltagefrequencyandamplitudeinfunctionoftheactiveandreactivepowerdeliveredbytheinverterThedroopmethodachieveshigherreliabilityandflexibilityinthephysicallocationofthemodules,sinceitusesonlylocalpowermeasurementsNevertheless,theconventionaldroopmethodshowsseveraldrawbacksthatlimititsapplicationarea,suchasslowtransientresponse,tradeoffbetweenthepowersharingaccuracyandthefrequencyandvoltagedeviations,unbalanceharmoniccurrentsharing,andhighdependencyontheinverteroutputimpedanceInaddition,thelineimpedanceisunknown,whichcanresultinreactivepowerunbalancesThisproblemcanbeovercomebyinjectinghighfrequencysignalsthroughthepowerlinesorbyaddingexternaldatacommunicationsignalsThesecommunicationsystems,typicallydigital,mustnotbecriticalandrobustThisway,controllerareanetworks,powerlinecommunications,orwireless(radiofrequencylinks)areoftenimplemented–Inthispaper,areviewofthecontrolschemesfortheparalleloperationofUPSsystemsandthetrendsofthesesystemsinDGsystemsandmicrogridsarepresentedAlthoughthecontrolofstandaloneUPSinverterswaswidelystudied,itwillnotbeshowninthispaper–ThispaperisorganizedasfollowsSectionIIdescribestheconfigurationtypesofdistributedUPSsystemsSectionIIIanalyzesthecirculatingcurrentproblemderivedfromtheparalleloperationofUPSinvertersSectionIVdepictstheactiveloadsharingtechniques,includingcentralizedcontrol,MScontrol,ALS,andCSectionVprovidesthedescriptionoftheconventionaldroopcontrolmethod,includingapowerflowanalysisThen,ageneralizationofthedroopmethod,thevirtualimpedanceloopapproach,andthemultiloopdroopcontroltechniquesaredescribedFinally,inSectionVI,acomparisonbetweenthecontroltechniquesandtheconclusionsisprovidedIICONFIGURATIONSOFDISTRIBUTEDUPSSYSTEMSDistributedUPSsystemssupportUPSunitsandcriticalloadsflexiblylocatedinaninterconnectedelectricalpowernetworkInordertoaddreliabilityandexpandabilitytothesystem,redundantandparallelUPSsystemsareusuallyintegratedintothepowersystemTherearetwomajortypesofdistributedUPSsystems(seeFig),ie,onlineandlineinteractivedistributedsystems$©IEEEIEEETRANSACTIONSONINDUSTRIALELECTRONICS,VOL,NO,AUGUSTFigDistributedUPSsystemconfigurations(a)Online(b)LineinteractiveThedistributedUPSsystemsarehighlyreliablebecauseofredundancyItisanadvantagetoachievetheNorNXredundancyinthesesystems,whereNUPSunitssupplytheload,andorXadditionalunitsstayinreserveTheyarealsohighlyflexibletoincreasethecapacityofthesystemwhenmorepowerisneeded,bysimplyaddingmoreUPSunitsARedundancyNorNXUPSUnitsTheredundancyconceptconsistsofhavingone(N)ormoreUPSunits(NX)inreserve,and,ifsomeoftherestoftheNmodulesaredamagedordisconnected,thisthesemodulescanautomaticallybeconnectedtosupplythefunctionsofthatunitTheredundancycanreducethesinglepointfailureAparallelredundantsystemcantypicallyprovideuptoavailability,whichmeansthatthesystemdoesnotoperateforlessthanhyearInadditiontohavingextraUPSmodules,theparallelredundantsystemneedstogivetheoperatorsomemeasureofsystemlevelfunctionalityThesimplestredundantUPSsystemistheparallelredundant,whichconsistsofusingacentralizedUPSwithonereservemoduleBParallelOperationofUPSSystemsTheproperparalleloperationoftheNmodulesthatconfigurethedistributedUPSsystemiscrucialGenerallyspeaking,aparalleledUPSsystemmustachievethefollowingfeatures,:)thesameoutputvoltageamplitude,frequency,andphase)equalcurrentsharingbetweentheunits)flexibilitytoincreasethenumberofunitsand)plugandplayoperationatanytime,alsoknownashotswapoperationcapabilityTheparalleloperationofUPShasanumberofadvantages,includingthermalmanagement,reliability,redundancy,modularity,maintainability,andsizereductionIIICIRCULATINGCURRENTANALYSISTheoutputcurrentsofeachUPSshouldbeequaloratleastproportionaltoitsnominalpowerratingThedifferenceFigCirculatingcurrentconceptbetweenthosecurrentsprovokescirculatingcurrentsamongtheUPSunitsThecirculatingcurrent(ic)isparticularlydangerousatnoloadorlightloadconditions,sinceoneorseveralmodulescanabsorbactivepoweroperatinginrectifiermode,asshownFigThiscurrentincreasesthedclinkvoltagelevel,whichcanresultindamagetothedclinkcapacitorsorinashutdownduetooverloadAnanalysisofthecirculatingcurrentcanbedonebyusingtheequivalentcircuitoftwoUPSunitsconnectedinparallel,sharingacommonloadTheanalysispresentedinthissectionwillbemadeusingphasors,beingonlyvalidundersinusoidalconditionsFollowingFig,wecandefinethecirculatingapparentpoweras∆S∆=S−S()and,consequently,theactiveandreactivecirculatingpowersare∆P∆=P−P()∆Q∆=Q−Q()AssumingthatL�ZoZL,L�ZoZL,andthatthetotaloutputimpedanceXT(LL)ismainlyinductive,GUERREROetal:CONTROLOFDISTRIBUTEDUNINTERRUPTIBLEPOWERSUPPLYSYSTEMSFigEquivalentcircuitoftwoUPSsconnectedinparallel,takingintoaccounttheoutputimpedanceoftheinverters(ZoandZo)andthepowerlineimpedances(�ZL=rLjωLand�ZL=rLjωL)then()and()canbesimplifiedas∆P∼=EEXTsin∆φ∼=EEXT∆φ()∆Q∼=VXT∆E()where∆φ=φ−φ,and∆E=E−EThus,theseequationscanbeexpressedinfunctionofthecurrentsinsteadofthepower,beingtheactiveandreactivecirculatingcurrents,as∆iP∼=EEVXT∆φ()∆iQ∼=∆EXT()Inconclusion,assuminganinductiveoutputimpedance,theactiveandreactivepowersorcurrentscanbecontrolledbyadjustingthephaseandamplitudeoftheoutputvoltageInordertotrytoavoidthecirculatingcurrent,thereexistanumberofcontrolstrategiesthatcanbeclassifiedinactiveloadsharinganddroopcontroltechniques,dependingontheuseornotofcommunicationlinksbetweenUPSunitsIVACTIVELOADSHARINGThefirstkindofcontrolscheme,namedtheactiveloadsharingtechnique,needsintercommunicationlinksAlthoughtheselinkslimittheflexibilityoftheUPSsystemanddegradeitsredundancy,bothtightcurrentsharingandlowoutputvoltagetotalharmonicdistortion(THD)canbeachievedThefollowingsectionprovidesareviewoftheexistingtechniquesforparallelinginvertersavailableintheliteratureTheactiveloadsharingtechniquescanbeclassifiedintofourdifferenttypes,ie,centralizedcontrol,,MS–,ALS–,andC,Usingthesetechniques,wewillgeneratethecurrentorpowerreferenceofeachmodule,whichiseasytoscaleaccordingtoitsnominalpowerratingACentralizedControlThiscontroltechnique,alsoknownasconcentratedcontrol,isdepictedinFigItconsistsofdividingthetotalloadcurrentiLbythenumberofmodulesN,sothatthisvaluebecomesthecurrentreference(i∗j)ofeachmodulej,i∗j=iLN,forj=,,N()FigBlockdiagramofacentralizedcontrollerforparalleledUPSsystemThecurrentreferencevalueissubtractedbythecurrentofeachmodule,obtainingthecurrenterror∆Ij,whichisprocessedthroughacurrentcontrolloopAnoutercontrolloopinthecentralizedcontroladjuststheloadvoltageThissystemisnormallyusedincommonUPSequipmentwithseveraloutputinvertersconnectedinparallelUsingthisapproach,itisnecessarytomeasurethetotalloadcurrentiL,soitcannotbeusedinalargedistributedsystemConsequently,acentralcontrolboardisnecessaryThecontrolimplementationcanfollowtwophilosophiesThefirstoneisexpressedby(),andthesecondistocalculatethecurrenterror∆i=i∗j−ijandtodecomposeitindirectcurrenterror∆ipandinquadraturecurrenterror∆iqFinally,∆ipand∆iqcanbeusedtoadjustthephaseandamplitudeoftheoutputvoltagereferenceofeachUPSunitTheotherpossibilityistouse∆iandtheoutputvoltagetocalculate∆Pand∆Qinsteadof∆ipand∆iq,asshowninFigBMSInthistechnique,themastermoduleregulatestheloadvoltageHence,themastercurrentiMfixesthecurrentreferencesoftherestofthemodules(slaves)asi∗S=iM,forS=,,N()Consequently,asshowninFig,themasteractsasavoltagesourceinverter(VSI),whereastheslaveworksasacurrentsourceinverter(CSI)Inthisconfiguration,ifthemasterunitfails,anothermodulewilltaketheroleofmasterinordertoavoidtheoverallfailureofthesystemThereexistdifferentvariantsofthiscontrolscheme,dependingontheroleofthemaster)Dedicated:themasterisonefixmodule)Rotary:themasterisarbitrarilychosen)Highcrestcurrent:themastercanbefixedbythemodulethatbringsthemaximumrmsorcrestcurrentUnitrodeICs,suchasUCorUC,areusedtoparalleldcdcconverters,implementingtheMSstrategyinwhichIEEETRANSACTIONSONINDUSTRIALELECTRONICS,VOL,NO,AUGUSTFigBlockdiagramofacentralizedcontrollerbasedonactiveandreactivepowerdeviationdecompositionFigMScontrolstrategy(a)Blockdiagramofthesystem(b)EquivalentcircuitoftheparallelUPSsystemcontrolledthroughtheMSstrategythemodulethatbringsthemaximumcurrentautomaticallybecomesthemasterThisstrategycanalsobeimplementedbyusingaverageactiveandreactivepowersasP∗S=PM,forS=,,N()Q∗S=QM,forS=,,N()Inthisparticularcase,andbyusingthehighestPandQaveragevalues,aschemesimilartothehighcrestcurrentcontrolstrategycanbeobtainedThiscontrolstrategyisshowninFig,andinthatcase,themasterUPSofPandQcanbedifferentmodulesMScontrolisoftenadoptedwhenusingdifferentUPSunitsmountedintoarackCALSThisisatruedemocraticcontrolschemeinwhicheverymoduletrackstheaveragecurrentdonebyalltheactivemodules–Thisscheme,showninFig(a),issimpletoimplementbyusingasinglewire,whichcontainstheaveragecurrentinformationcomputedbyaresistorconnectedtothecurrentsensorofeverysinglemoduleInaddition,adjustingtheresistortoapropervalue,wecanparallelconverterswithdifferentpowerratingThiscontroltechniquestartsfromanideaappliedtoparalleldcdcconvertersbyusingcurrentsharingresistorsconnectedtoacommoninformationbusThecurrentofallmodulesisaveragedbymeansofacommoncurrentbusTheaveragecurrentofallthemodulesisthereferenceforeachindividualoneThiscontrolschemeishighlyreliableduetotherealdemocraticconception,inwhichnoMSphilosophyispresentInaddition,theapproachishighlymodularandexpandable,makingitinterestingforindustrialUPSsystemsIngeneral,thisschemeisthemostrobustandusefuloftheaforementionedcontrollersAvariantofthistechniqueisthecurrentweightingdistributioncontrolThecurrentreferenceofeachmodulecanbeexpressedasi∗k=NN∑j=ij,fork=,,N()ThiscontrolapproachcanbeperformedbyusinganinneroranoutercurrentloopTheproblemwithusinganouterloopGUERREROetal:CONTROLOFDISTRIBUTEDUNINTERRUPTIBLEPOWERSUPPLYSYSTEMSFigAutoMS(highestcrestPQmaster)powersharingcontrolschemeisthatduetothat,thevoltageloophasanarrowbandwidth,andinordertoavoidinstabilities,thecurrentloopneedsacompensatorAsaconsequenceofthebandwidthreductionofthisloop,thecurrentdynamicsisveryslow,provokingpoorcurrentsharingduringtransientsAsusual,anotherpossibilityistouseactiveandreactivepowerinformationinsteadofthecurrentThus,weuseactiveandreactivepowertoadjustthephaseandamplitudeofeachmoduleFig(b)showstheblockdiagramoftheaveragepowersharingtechniqueUsingthistechnique,eachUPSunitcontrolstheactiveandreactivepowerflowinordertomatchtheaverageactiveandreactivepowersofthesystembyadjustingthephaseandtheamplitudeofitsowninneroutputvoltagereferenceTheactiveandreactivepowercanbeobtainedthroughthedirectandreactivecomponentdecompositionoftheoutputcurrentTheaverageactiveandreactivepowerreferencesofeachmodulecanbeexpressedasP∗k=NN∑j=Pj()Q∗k=NN∑j=Qj,fork=,,N()AnearlierworkusesthismethodtoachievethepowersharingbetweentwoUPSmodulesThiscontrolschemecanbeextendedtomoreunitsbyusingtheactiveandreactiveaveragepowersharingbusesNoticethatthistechniquedoesnotrequireanymasterorslaveunit,andonlylowbandwidthdigitalcommunicationsarerequiredtoachievegoodPandQsharingNevertheless,itonlyactsoverthefundamentalcomponentoftheoutputcurrent,misleadingtheharmoniccontentHence,unbalancesbetweenthepowerstagesandthepowerlinescanproducelargecirculatingharmoniccurrentbetweentheunitsDCThiscontrolscheme,showninFig,consistsofthecurrentreferenceofeachmoduletakenfromtheaforementionedmodule,formingacontrolringNotethatthecurrentreferenceofthefirstunitisobtainedfromthatofthelastunittoformacircularchainconnectionThisstrategycanbeexpressedthroughi∗=iN()i∗k=ik−,fork=,,N()TheapproachcanbeinterestingfordistributedpowersystemsbasedonacpowerringsduetothedistributionofpowerlinesFigillustratestheexampleofadistributedringformingUPSsystemTherearetwolinesinordertoachievebidirectionalcommunicationandtoincreasesystemreliabilityIEEETRANSACTIONSONINDUSTRIALELECTRONICS,VOL,NO,AUGUSTFigALScontrolschemes(a)Averagecurrentsharing(b)AveragepowersharingGUERREROetal:CONTROLOFDISTRIBUTEDUNINTERRUPTIBLEPOWERSUPPLYSYSTEMSFigBlockdiagramofthecurrentchaincontrol(C)FigCommunicationlinksofthecurrentchaincontrol(C)ThecurrentlimitationcontrolisavariantoftheCInthiscase,theloadvoltageiscontrolledbythemastermodule,whereastheslavemodulesareonlyforsharingtheloadcurrentExceptforthemastermodule,thecurrentcommandoftheslaveisgeneratedbyitspreviousmoduleandlimitedinamplitudeInthisscheme,anymodulecanbethemaster(dedicated,rotating,orhighcrestcurrent)TheconnectionofallcontrolcircuitscanformacircularchainconnectionsuchthateverymodulemaybecomethemasterFigEquivalentcircuitofaUPSinverterconnectedtoacommonacbusVDROOPCONTROLMETHODThesecondkindofcontrolscheme,namedthedroopcontrolmethod,isabletoavoidcriticalcommunicationlinksTheabsenceofcriticalcommunicationsbetweenthemodulesimprovesthereliabilitywithoutrestrictingthephysicallocationofthemodules–Intheliterature,thedroopmethodisalsocalledindependent,autonomous,orwirelesscontrolThedroopmethodisbasedonawellknownconceptinlargescalepowersystems,whichconsistsofdroopingthefrequencyoftheacgeneratorwhenitsoutputpowerincreasesInthecaseofparallelconnectedUPSinverters,theactiveandreactivepowerssuppliedtotheacbusaresensedandaveraged,andtheresultingsignalsareusedtoadjustthefrequencyandamplitudeoftheUPSinverteroutputvoltagereferenceThedroopmethodachieveshigherreliabilityandflexibilityinthephysicallocationofthemodulessinceitonlyuseslocalpowermeasurementsAActiveandReactivePowerDroopControlTraditionally,theinverteroutputimpedanceisconsideredtobeinductiveduetothehighinductive

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