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Topic6:MultilevelcascadedH-bridgeinverter1CHBInverterFedDriveH-bridepowercellsSource:Toshiba-GeneralElectricTopic6:MultilevelCHBinverterH-BridgeInverterCHBInverterTopologiesPhaseShiftedPWMLevelShiftedPWMPWMSchemeComparison2Topic6:MultilevelCHBinverter3WhyUseMultilevelInverters?•Toincreaseinverteroperatingvoltagewithoutdevicesinseries•TominimizeTHDwithlowswitchingfrequenciesfsw•ToreduceEMIduetolowervoltagestepsSwitchingfrequencyforhighpowerconverters:fsw=60Hz~1000HzMultilevelInverterTopologies4Per-PhaseDiagramH-BridgeInverter5H-bridgePowerCellH-BridgeInverter6TypicalIndustrialApplicationsFive-levelCHBinverterH-bridgePowerCellH-BridgeInverter7BipolarModulationBipolarPWM:vABfrom-Vdto+Vdorfrom+Vdto-VdH-BridgeInverter8BipolarModulation(FFT)H-BridgeInverter9UnipolarModulation(1)•Twomodulationwavesvmandvm-•Onecarrierwavevcr•UnipolarPWM:vABfrom0to+Vdorfrom0to-VdH-BridgeInverter10UnipolarModulation(2)•Onemodulationwaves:vm•Twocarrierwave:vcr
andvm-CHBInverterTopologies11Five-LevelCHBInverterComplementarySwitchpairs:S11andS41;S31andS21;S12andS42;S32andS22;Note:Convertersincascade,butnoswitchingdevicesinseries.CHBInverterTopologies12OutputVoltageandSwitchingStatus(five-level)WaveformofvANiscomposedoffivevoltagelevels:2E,E,0,-E,and-2E.CHBInverterTopologies13Seven-andNine-LevelInverters(Perphasediagram)CHBInverterTopologies14UnequaldcBusVoltagesCHBInverterTopologies15UnequaldcBusVoltages(Two-cellseven-leveltopology)PhaseShiftedPWM16CarrierBasedPWM–PhaseShifted•#ofvoltagelevels:m=7•#ofcarriers:mc=m-1=6•Phaseshift:360°/mc=60°CarriersforH1bridge: vcr1andvcr1-CarriersforH2bridge: vcr2andvcr2-CarriersforH3bridge: vcr3andvcr3-m=7PhaseShiftedPWM17InverterWaveforms(7-level,phaseshifted)•Switchingoccursatdifferenttimes•fsw(device)=60mf=600Hz•Inverterphasevoltagelevels:7•LowEMI•Line-to-linevoltagelevels:13•Closetoasinusoid•LowTHDPhaseShiftedPWM18FFT(7-level,phaseshifted)•Lowestharmonics:around2mf•Lowestharmonics:around6mf•ContainingtriplenHarmonics•Notriplen
harmonics•Equivalentfsw(inverter)=60(6mf)=3600HzPhaseShiftedPWM19HarmonicContent(7-level,phaseshifted)LevelShiftedPWM20CarrierBasedPWM–LevelShifted•#ofvoltagelevels:
m=5•#ofcarriers:
mc=m-1=4Note:IPDprovidesthebestharmonicprofile.IPD:APOD:POD:LevelShiftedPWM21GatingArrangement(7-level)•#ofvoltagelevels:m=7•#ofcarriers:mc=m-1=6•fsw(device):-notequaltofcr,and-notthesameforallswitches.•Deviceconductionangle:-notequal.•Necessarytoswapswitchingpattern.LevelShiftedPWM22InverterOutputVoltages(7-level)•m=7•Switchingoccursatdifferenttimes•fsw(device)=fcr/mc=600Hz(avg)•vABclosetoasinusoid•LowTHD,lowEMI•fsw(inv)=fc=3600HzLevelShiftedPWM23PrototypeatRyerson(7-levelCHB)LevelShiftedPWM24MeasuredWaveforms(IPD,7-levelCHB)InverterphasevoltagevANLine-to-linevoltagevABPWMSchemeComparison25PWMatLowma•Atma=0.2:-PhaseshiftedPWM:THD=96.7%-LevelshiftedPWM:THD=48.8%PWMSchemeComparison26TotalHarmonicDistortion(THD)PWMSchemeComparison27SummaryTopic7:MultilevelNeutralPointClampedInverter28Three-LevelNPCInverterBasedMVDriveSource:ABB(ACS1000)Topic7:MultilevelNPCInvertersThree-levelNPCInverterSpaceVectorModulationNeutralPointVoltageControlHigh-levelNPCInverters29MultilevelInverterTopologies30Per-PhaseDiagramMultilevelNPCInverters31InverterConfigurationClampingdiodes:DZ1andDZ2(PhaseA)MultilevelNPCInverters32SwitchingStateComplementarySwitchpairs:S1andS3;S2andS4;MultilevelNPCInverters33GateSignalArrangementsInverterphasevoltagevAZhasthreelevels:E,0and–EMultilevelNPCInverters34InverterOutputWaveformsSpaceVectorModulation35SpaceVectors•Three-phasevoltages
(1)•Two-phasevoltages(2)•Spacevectorrepresentation(3)(2)(3)
(4)whereSpaceVectorModulation36SpaceVectors(Example)Switchingstate[POO]on-stateswitches:PhaseA:uppertwoswitches[P]PhaseB:middletwoswitches[O]PhaseC:middletwoswitches[O]Fromwhich
and
(5)•Substituting(5)to(4)givesaspacevector(6)Totalswitchingstates:27Totalspacevectors:19SpaceVectorModulation37SpaceVectorsDiagram19spacevectors:Zerovector:V0Smallvectors:V1–V6Mediumvectors:V7–V12Largevectors:V13–V18SpaceVectorModulation38SwitchingStatesandSpaceVectorsRedundancy:Zerovector–threeswitchingstatesSmallvectors–twostatespervectorSpaceVectorModulation39SwitchingStatesandSpaceVectorsNoredundantswitchingstatesformediumorlargevectorsSpaceVectorModulation40SectorDefinition•Vref:Referencevector,rotatinginspaceatacertainspeed;•Allothervectorsarestationary.SpaceVectorModulation41SVMPrinciple•Foragivenlengthandpositioninspace,Vrefcanbeapproximatedbythreenearbystationaryvectors;•Basedonthechosenstationaryvectors,switchingstatesareselectedandgatesignalsaregenerated;•WhenVrefpassesthroughsectorsonebyone,differentsetsofswitchesareturnedonoroff;•WhenVrefrotatesonerevolutioninspace,theinverteroutputvoltagevariesonecycleovertime;•TheinverteroutputfrequencycorrespondstotherotatingspeedofVref;•TheinverteroutputvoltagecanbeadjustedbythemagnitudeofVref.SpaceVectorModulation42SectorDefinition•Vref:Referencevector,rotatinginspaceatacertainspeed;•Allothervectorsarestationary.SpaceVectorModulation43DwellTimeCalculationDwelltimeistheduty-cycletimeofselectedswitchesduringthesamplingperiodTs.•Selectthreeneareststationaryvectors•Usevolt-secondbalancingprinciple(a)SectorIFourRegionsSpaceVectorModulation44DwellTimeCalculation•Fromequation(a)Ta,TbandTc–dwelltimesforV1,V7andV2–modulationindex
SpaceVectorModulation45SwitchingSequence(Seven-segment)•GeneralDesignRequirementsa)Thetransitionfromoneswitchingstatetothenextinvolvesonlytwoswitchesinthesameinverterleg,onebeingturnedonandtheotherturnedoff;andb)ThetransitionforVrefmovingfromonesector(oroneregion)tothenextrequiresnoorminimumnumberofswitchings.Note:Theswitchingsequencedesignisnotunique,buttheaboverequirementsshouldbesatisfiedforswitchingfrequencyminimization.SpaceVectorModulation46SwitchingSequence(Seven-segment)•AssumingVrefisinRegion4ofSectorI,threevectorsareselected:V2,V7andV14SpaceVectorModulation47SwitchingSequence(Seven-segment)Note:Switchingsequencerequirementa)issatisfied.SpaceVectorModulation48SwitchingSequence(Seven-segment)SpaceVectorModulation49SwitchingSequence(Seven-segment)Note:Switchingsequencerequirementb)issatisfied.•Deviceswitchingfrequency:•Samplingfrequency:•Fundamentalfrequency:SpaceVectorModulation50SimulatedWaveforms(Seven-segment)•Deviceswitchingf1=60Hz,Ts=1/1080sec,ma=0.8,fsw=570Hz•vABisnothalfwavesymmetrical;andcontainsbotheven-andodd-orderharmonics.SpaceVectorModulation51SimulatedWaveforms(Seven-segment)f1=60Hz,Ts=1/1080sec,ma=0.8,fsw=570HzSpaceVectorModulation52HarmonicContent(Seven-segment)SpaceVectorModulation53LaboratoryPrototypeatRyersonSpaceVectorModulation54MeasuredWaveformsSpaceVectorModulation55MeasuredWaveforms(witheven-orderharmonicelimination)NeutralPointVoltageControl56NeutralPointVoltageDeviationTheneutralpointvoltagevzcanbecontrolledbyP-andN-typesofsmallvectorsNeutralPointVolt
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