1Chapter18：OptimizingtheUtilityInterfacewithPowerElectronicSystems18-1Introduction18-6ImprovedSingle-PhaseUtilityInterface18-7ImprovedThree-PhaseUtilityInterface218-1IntroductionPowerqualityhasbecomeanimportantissueDiode-RectifierBridge1GenerationofCurrentHarmonics3Diode-RectifierBridgewaveform4Diode-RectifierBridgewaveform5TypicalHarmonicsintheInputCurrent

Single-phasediode-rectifierbridge6Duetoharmoniccurrentsinjectedintotheutilitygrid,thevoltagewaveformatthepointofcommoncouplingwillbecomedistortion.

PCCisthepointofcommoncoupling2Deleteriouseffectsofharmoniccurrent7DeleteriouseffectsofharmonicdistortionandapoorPowerFactorIncreasingpowerlossintransmissionlines,transformers,generators.Overloadingtheshuntcapacitorsusedbyutilitiesforvoltagesupport.maycausingresonanceconditionsbetweenthecapacitivereactanceoftheshuntcapacitorsandtheinductivereactanceofthetransmissionlines.Theutilityvoltagewaveformwillalsobecomedistorted,adverselyaffectingotherlinearloads.Resultinginerrorsinmetering,malfunctionofutilityrelays,interferencewithcommunicationandcontrolsignals,andsoon.83HarmonicGuidelines:IEEE519Commonlyusedforspecifyinglimitsontheinputcurrentdistortion9Limitsondistortionintheinputvoltagesuppliedbytheutility3HarmonicGuidelines:IEEE5191018-6Improvedsingle-PhaseUtilityInterface18-6-1passivefiltersTheaddedinductorresultsinahighereffectivevalueoftheac-sideinductanceLs,whichimprovethepowerfactorandreducesharmonics.1112

TheeffectofLsondioderectifierwithacapacitor:☆Thepowerfactorisimprovedfromverypoortosomewhatacceptable.Harmonicsaredecreased.TheoutputvoltageVdislowercomparedwiththeno-inductancecase.Theoverallenergyefficiencyremainsessentiallythesame;thereareadditionallossesintheinductor,buttheconductionlossesinthediodesarelower.1318-6-2Power-Factor-Correction(PFC)CircuitBetweentheutilitysupplyanddc-buscapacitor,aBoostdc-dcconverterisintroduced.Useaboostdc-dcconvertertoshapetherectifiedcurrent.141OperationprincipleofPFCBypulse-width-modulatingthetransistorataconstantswitchingfrequency,thecurrentiLthroughtheLdisshapedtohavethefull-wave-rectifiedwaveform.SimilartoTheinputcurrentisissinusoidal,andinphasewiththesupplyvoltagevs.15BecauseofafairlylargeCd,vd(t)=Vd.Therefore,16IfLdisverysmall,thenpin(t)=pd(t).Therefore,OutputcurrentconsistsofdccomponentIdandsecondharmoniccomponent.17tominimizetherippleofvd

anappropriatevalueofCdmustbechosen.Aseries-tunedLCfiltertunedfortwicetheacfrequencymaybeputinparallelwithCd.18Note:

Vdmustbegreaterthanthepeakofthesupplyvoltage.192ControlofPFC(1)

themaincontrolobjectives①todrawasinusoidalcurrent,inphasewiththeutilityvoltage;②tomaintainVdatthereferencevalue.RFI1CiLLDTC++-ACAiLiLoadVdPFCcontrolloopV*dARVdPWMcontrolMultipileri*LKL20Thecontrolobjectives

leadtotwocontrolloops:Theinnercurrentloopensurestheformofi*L(t)basedontheutilityvoltageis(t).Theoutervoltageloopdeterminestheamplitudeofi*L(t)basedonthevoltagefeedbackandregulatesthevoltageofthePFCtothepre-selecteddcvoltage.RFI1CiLLDTC++-ACAiLiLoadVdPFCcontrolloopV*dARVdPWMcontrolMultipileri*LKL21Note:Theinnercurrentloopisrequiredtohaveaveryhighbandwidthcomparedtheoutervoltageloop.hence,eachloopcanbedesignedseparately.22(2)Voltageloopcontrolprinciple:IfILoad↑→Vd

↓(<V*d)→KL↑→i*L↑→iL↑→inputpower↑→Vd↑,henceensuresVd=const.RFI1CiLLDTC++-ACAiLiLoadVdPFCcontrolloopV*dARVdPWMcontrolMultipileri*LKL23(3)CurrentloopcontrolTherearevariouswaystoimplementthecurrentloopcontrol:DirectcurrentcontrolConstant-frequencycontrolConstant-tolerance-bandcontrolVariable-tolerance-bandcontrolDiscontinuous-currentcontrolIndirectcurrentcontrol24①Constant-frequencycontrolTheswitchinthestep-upconverteristurnedonbyaclockatfixedfrequencyfs,wheniLreachesi*L,theswitchisturnedoff.25②Constant-tolerance-bandcontrol2618-6-3InterfaceforaBidirectionalpowerflow1ThyristorConvertersfor4-QuadrantOperationTheinputcurrentishasadistortedandthepowerfactorislow.272Switch-ModeConverterInterface28Inthecircuit:Single-phasevoltagesourcePWMconverterD1D3D4D2T1T3T4T2isLsvsvconvABL2C2Cd+-Vd+vL-29Assumingvstobesinusoidal,atthelinefrequencyω=2πf,(1)Phasorequation:(2)Phasordiagram:30(3)Theimportantequations:ForagivenvsandthechosenLs,PandQcanbeobtainedbycontrollingthemagnitudeandthephaseofvconv1.31(4)Switch-ModeConverterControlTherearevariouswaystoimplementthecurrentloopcontrol:IndirectcurrentcontrolDirectcurrentcontrol32①IndirectCurrentControl-----Baseonphasorequation:

Rectifiermode33Inversionmode34Waveformsintherectifiermode35Waveformsintherectifiermodevconvvconv1vsis36Waveformsintheinversionmodevconvvconv1is37Waveformsinthezeroloadmodevconvvconv1is38②DirectCurrentControlSingle-phasevoltagesourcePWMconverterD1D3D4D2T1T3T4T2isLsvsvconvABL2C2Cd+-Vd+vL-Note:Vdmustbegreaterthanthepeakofthesupplyvoltage.3918-7ImprovedThree-PhaseUtilityInterface

RectifierandInvertermodesbasedonthedirectionofpowerflow40Forrectificationataunitypowerfactor,Φ1=0,and41Applications1T2TAppliedinelectriclocomotivesvsLsA1D2D2C+-3T4TB3D4DdC2LVddIvconv42BPNACC1CdLsLsLsLSalorArray43Supplementalmaterial-----ActivePowerFilterS18-1:Thefollowingfigureshowsthesingle-phasevoltagesourcePWMconverter’scircuitdiagram,wecanrealizebidirectionalpowerflowbythiscircuit