电力电子装置及系统 课件 Topic 8-Pulse-width-modulation current source inverter、Topic 9-Modular multilevel converter

Topic8:PWMCurrentSourceInverter1PWMCSIfedMVdriveSource:RockwellAutomationTopic8:PWMCurrentSourceInverterSingleBridgeInverterTrapezoidalModulation(TPWM)SelectiveHarmonicElimination(SHE)SpaceVectorModulation(SVM)DualBridgeInverter2SingleBridgeInverter3InverterTopologyFeatures:-Simpletopology–noantiparalleldiodes-Reliableshortcircuitprotection–constantdccurrent-Verylowdv/dtonmotorterminalsSymmetricalGCTsFunctionofCf

:-AssistGCTcommutation-ReduceharmonicdistortionSingleBridgeInverter4DCCurrentSourceIdImplementationofdccurrentsource:-usealargesizedcchoke–makingIdsmooth;-usedccurrentfeedbackcontrol–keepingIdconstantSingleBridgeInverter5ModulationTechniques•TrapezoidalPWM(TPWM)•SelectiveHarmonicElimination(SHE)•SpaceVectorModulation(SVM)•ConstraintsonSwitchingPatternDesign-dccurrentId

cannotbeinterrupted-inverteroutputcurrentwaveformmustbedefined.•Atanytimeinstant,onlytwoswitchesareturnedon,oneconnectedtothepositivedcbus,andtheothertothenegativedcbus.TrapezoidalModulation6TrapezoidalPWM(TPWM)Numberofpulsesperhalfcycle:Np=7TrapezoidalModulation7HarmonicContent(TPWM)•Np=15•Fundamentaldoesnotchangemuchwithma•ma=0.85TrapezoidalModulation8Waveforms(TPWM)SelectiveHarmonicElimination(SHE)9Principle•Notalltheswitchinganglesareindependent.•OnlytwoharmonicscanbeeliminatedwithNp=5.•Numberofharmonicstobeeliminated:•Nomodulationindexcontrol–themagnitudeofinverteroutputcurrentiscontrolledbyIdSelectiveHarmonicElimination10FourierAnalysisSelectiveHarmonicElimination11FourierAnalysisExpressionforanSelectiveHarmonicElimination12SwitchingAngleCalculationToEliminatenthharmonic,setan=0For5th,7thand11thharmonicelimination:SelectiveHarmonicElimination13SwitchingAngle(SHE)SelectiveHarmonicElimination14InverterWaveforms(SHE)Harmoniceliminated:5th,7thand11th;fsw=420HzSelectiveHarmonicElimination15Waveforms(SHE)SpaceVectorModulation16SpaceVectorModulation•Sixactivecurrentvectorsandonezerovector•SixsectorsSpaceVectorModulation17SwitchingStateSpaceVectorModulation18SwitchingStates&SpaceVectors[1]:Upperswitchon[-1]:Lowerswitchon[0]:Noneoftheswitchesinalegturnedon[2]:Bothswitchesinalegturnedon(bypassmode)SpaceVectorModulation19DwellTimeCalculationFollowingthesameprincipleofSVMfortheNPCinverterSpaceVectorModulation20DwellTimeCalculationSpaceVectorModulation21SwitchingSequenceRequirements:1)Transitionfromoneswitchingstatetothenextinvolvesonlytwoswitches;2)Atanytimeonlytwoswitchesareon.SpaceVectorModulation22SwitchingSequence(Overonecycle)SpaceVectorModulation23InverterOutputWaveforms(SVM)f1=60Hz,fsw=540Hz,Np=9andma=1SpaceVectorModulation24HarmonicSpectrum(SVM)f1=60Hz,fsw=540Hz,Np=9andma=1SpaceVectorModulation25HarmonicSpectrum(SVM)Dual-BridgeInverter26ConverterConfigurationDual-BridgeInverter27SpaceVectorDiagram19vectorsand51switchingstatesDual-BridgeInverter28DCCurrentBalanceControlCurrentpathswithswitchingstate[16;56]Dual-BridgeInverter29DCCurrentBalanceControlCurrentpathswithswitchingstate[16;56]Dual-BridgeInverter30ExperimentalWaveformsSummary31PWMSchemeComparisonTopic9:ModularMultilevelConverter32SiemensHVDCPLUSSource:SiemensTopic10:TransformerlessPhotovoltaicInverters33SiemensHVDCPLUSSource:SiemensModularMultilevelConverters34Convertertopology(per-phasediagram)MarquardtRainer,univ.Prof.,Dr.-InUniversitätderBundeswehr

MünchenHowMMCworks?UpperArmVoltageLowerArmVoltage+0.5Ud-0.5UdAtthistimepoint,voltagelevelproducedUpperArmVoltageLowerArmVoltageAtthistimepoint,voltagelevelproduced+0.5Ud-0.5Ud+0.5Ud-0.5UdHowMMCworks?UpperArmVoltageLowerArmVoltageAtthistimepoint,voltagelevelproduced+0.5Ud-0.5UdHowMMCworks?UpperArmVoltageLowerArmVoltage+0.5Ud-0.5UdAtthistimepoint,voltagelevelproduced+0.5Ud-0.5UdHowMMCworks?UpperArmVoltageLowerArmVoltage+0.5Ud-0.5UdAtthistimepoint,voltagelevelproduced+0.5Ud-0.5UdHowMMCworks?UpperArmVoltageLowerArmVoltage+0.5Ud-0.5UdAtthistimepoint,voltagelevelproduced+0.5Ud-0.5UdHowMMCworks?UpperArmVoltageLowerArmVoltage+0.5Ud-0.5UdAtthistimepoint,voltagelevelproduced+0.5Ud-0.5UdHowMMCworks?UpperArmVoltageLowerArmVoltage+0.5Ud-0.5UdAtthistimepoint,voltagelevelproduced+0.5Ud-0.5UdHowMMCworks?ModularMultilevelConverters44Mainfeatures‐Modulardesignforcostreduction‐Voltagescalability–fromafewkVtoafewhundredkV‐Singledclink–suitableforback-to-backconfiguration‐SinusoidalinputsandoutputsOutputwaveformsofa7LMMCinverterModularMultilevelConverters45Maintechnicalissues‐Voltagebalancingofflyingcapacitors‐Needspre-chargingcircuits‐Problemsatlow‐frequencyoperationModularMultilevelConverters46CapacitorvoltagebalancingcontrolPrinciple:UseredundantswitchingstatestocontrolthecapvoltageExample:ModularMultilevelConverters47Cappre-charging–fromthegridsideMainfeature:Capableofpre-chargingthecapacitorsinbothrectifierandinverterMaindrawback:Highcost-itrequiresa3-phaseMVbypassswitch/contactorSchandchargingresistorsRch.MVcontactor:ModularMultilevelConverters48Cappre-charging–inthearm(per-phasediagram)Maindrawback:Highcost–morebypassswitchSch

andchargingresistorsRchthanthepre-chargingfromthegridsideModularMultilevelConverters49Cappre-charging–inthedclinkFeature:Apre-chargingcircuitforbothrectifierandinverter.Drawback:‐DCsupplyvoltageVchisatthemediumvoltagelevel:fora6kV7LMMC-feddrive,Vch=3.3kV(with3halfbridgecellsperarm)‐Notsuitableformoduleswithdifferentcapacitorvoltages(suchas3LFCcells)ModularMultilevelConverters50Cappre-charging–inthedclinkFeature:Simplecircuitswithonlyabypassswitchandachargingresistor.Drawback:‐Thebypassswitchandchargingresistorareatthemediumvoltagelevel.‐Itcanbeonlyusedtochargethecapacitorsintheinverteronly.ModularMultilevelConverters51Cappre-charging–anovelsolutionRequirements:anypossibilitiestodevelopapre-chargingcircuitwiththefollowfeatures:‐Useasimplelow‐voltagecircuit,e.g.<200V,forcostreduction‐Nobypassswitches,nochargingresistors‐Capableofpre-chargingallthecapacitorsinbothrectifierandinverterModularMultilevelConverters52Cappre-charging–anovelsolutionPre-chargecircuitusingalow-voltagedcsourceTwooperationmodesforchargingSMcapacitorsonebyone:(a)bypassmodeand(b)insertmode.ModularMultilevelConverters53Cappre-charging–anovelsolutionThree-levelFCSM:bypassmodeinsertmodeIinsertmodeII.TwooperationmodesforchargingSMcapacitorstwobytwo:(a)bypassmodeand(b)insertmode.ModularMultilevelConverters54Precharging-experimentalresults(half-bridgeSMs)OnebyoneTwobytwoDc-sourcevoltage,chargingcurrent,andcapacitorvoltagesVc1−Vc2

CapacitorvoltagesVc3−Vc6

CapacitorvoltagesVc7−Vc8

ModularMultilevelConverters55Problemsatlow‐frequencyoperationProblems:‐Highvoltageripplesontheflyingcapacitorsduetolowfundamenta