STATCOM-原理介绍-动态无功补偿原理介绍

24/08/2007STATCOM(StaticSynchronousCompensator)Itisadeviceconnectedinderivation,basicallycomposedofacouplingtransformer,thatservesoflinkbetweentheelectricalpowersystem(EPS)andthevoltagesynchronouscontroller(VSC),thatgeneratesthevoltagewavecomparingittotheoneoftheelectricsystemtorealizetheexchangeofreactivepower.ThecontrolsystemoftheSTATCOMadjustsateachmomenttheinversevoltagesothatthecurrentinjectedInthenetworkisincuadraturetothenetworkvoltage,intheseconditionsP=0andQ=0.Initsmostgeneralway,theSTATCOMcanbemodeledasaregulatedvoltagesourceViconnectedtoavoltagebarVsthroughatransformer.Donsión24/08/2007STATCOM(StaticSynchronousCompensator)STATCOM-AVSCinterfacedinshunttoatransmissionlineTheSTATicCOMpensator(STATCOM)usesaVSCinterfacedinshunttoatransmissionline.InmostcasestheDCvoltagesupportfortheVSCwillbeprovidedbytheDCcapacitorofrelativelysmallenergystoragecapability-hence,insteadystateoperation,activepowerexchangedwiththelinehastobemaintainedatzero,asshownsymbolicallyintheFigure.Donsión24/08/2007STATCOM(StaticSynchronousCompensator)STATCOM-AVSCinterfacedinshunttoatransmissionlineWiththeactivepowerconstraintimposed,thecontroloftheSTATCOMisreducedtoonedegreeoffreedom,whichisusedtocontroltheamountofreactivepowerexchangedwiththeline.Accordingly,aSTATCOMisoperatedasafunctionalequivalentofastaticVARcompensator;itprovidesfastercontrolthananSVCandimprovedcontrolrange.Donsión24/08/2007STATCOM(StaticSynchronousCompensator)EachGTOconvertergeneratesavoltagethatissteppedupbyaline-side-series-connectedmulti-stageconvertertransformer.Theconvertertransformerenablesthebuild-upofasine-wavevoltageinbothmagnitudeandphase.BecauseSTATCOMswithmulti-stageconvertertransformersdonotgeneratesignificantinternalharmonics,theygenerallyrequireminimal,orno,harmonicfiltering.IfthenumberoffiringpulsesfortheGTOsisincreased(i.e.,pulse-widthmodulation(PWM)order),theharmonicsarefurtherdecreased.High-sidevoltageisgenerallyusedasacontrollerinput,asindicatedinthefigure.Donsión24/08/2007STATCOM(StaticSynchronousCompensator)ThefigureshowstheequivalentcircuitofaSTATCOMsystem.TheGTOconverterwithadcvoltagesourceandthepowersystemareillustratedasvariableacvoltagesinthisfigure.Thesetwovoltagesareconnectedbyareactancerepresentingthetransformerleakageinductance.EquivalentcircuitofaSTATCOMDonsión24/08/2007STATCOM(StaticSynchronousCompensator)UsingtheclassicalequationsthatdescribetheactiveandreactivepowerflowinalineintermsofViandVs,thetransformerimpedance(whichcanbeassumedasideal)andtheangledifferencebetweenbothbars,wecandefinedPandQ.TheanglebetweentheVsandViinthesystemisd.WhentheSTATCOMoperateswithd=0wecanseehowtheactivepowersendtothesystemdevicebecomeszerowhilethereactivepowerwillmainlydependonthevoltagemodule.Thisoperationconditionmeansthatthecurrentthatgoesthroughthetransformermusthavea+/-90ºphasedifferencetoVs.Inotherwords,ifViisbiggerthanVs,thereactivewillbesendtotheSTATCOMofthesystem(capacitiveoperation),originatingacurrentflowinthisdirection.Inthecontrarycase,thereactivewillbeabsorbedfromthesystemthroughtheSTATCOM(inductiveoperation)andthecurrentwillflowintheoppositedirection.FinallyifthemodulesofVsandViareequal,therewon´tbenorcurrentnorreactiveflowinthesystem.Thus,wecansaythatinastationarystateQonlydependsonthemoduledifferencebetweenVsandVivoltages.TheamountofthereactivepowerisproportionaltothevoltagedifferencebetweenVsandVi.Donsión24/08/2007STATCOM(StaticSynchronousCompensator)PrincipleofoperationofaSTATCOMTherecanbealittleactivepowerexchangebetweentheSTATCOMandtheEPS.TheexchangebetweentheinverterandtheACsystemcanbecontrolledadjustingtheoutputvoltageanglefromtheinvertertothevoltageangleoftheACsystem.ThismeansthattheinvertercannotprovideactivepowertotheACsystemformtheDCaccumulatedenergyiftheoutputvoltageoftheinvertergoesbeforethevoltageoftheACsystem.Ontheotherhand,theinvertercanabsorbtheactivepoweroftheACsystemifitsvoltageisdelayedinrespecttotheACsystemvoltage.Donsión24/08/2007STATCOM(StaticSynchronousCompensator)V-IcharacteristicofaSTATCOMTheSTATCOMsmoothlyandcontinuouslycontrolsvoltagefromV1toV2.However,ifthesystemvoltageexceedsalow-voltage(V1)orhigh-voltagelimit(V2),theSTATCOMactsasaconstantcurrentsourcebycontrollingtheconvertervoltage(Vi)appropriately.Thus,whenoperatingatitsvoltagelimits,theamountofreactivepowercompensationprovidedbytheSTATCOMismorethanthemost-commoncompetingFACTScontroller,namelytheStaticVarCompensator(SVC).Thisisbecauseatalowvoltagelimit,thereactivepowerdropsoffasthesquareofthevoltagefortheSVC,whereMvar=f(BV2),butdropsofflinearlywiththeSTATCOM,whereMvar=f(VI).ThismakesthereactivepowercontrollabilityoftheSTATCOMsuperiortothatoftheSVC,particularlyduringtimesofsystemdistress.Donsión24/08/2007STATCOM(StaticSynchronousCompensator)InadditiontheSTATCOMhasotheradvantagescomparedtoanSVC,suchas:•Quickerresponsetime(ASTATCOMhasastepresponseof8msto30ms).Thishelpswithcompensationofnegativephasecurrentandwiththereductionofvoltageflicker.•ActivepowercontrolispossiblewithaSTATCOM(withoptionalenergystorageondccircuit).Thiscouldfurtherhelpwithsystemst