电力电子技术（第5版）(英文版)课件：PWM控制技术

Power

Electronics

PWM控制技术

PWMTechniquesThemostwidelyusedcontroltechniqueinpowerelectronicsPulseWidthModulation(PWM)(Choppingcontrol)DC/DCAC/ACDC/ACAC/DCOutline7.1Basicprinciples7.2SomemajorPWMtechniquesinDC/ACinverters

7.3PWMtechniqueswithfeedbackcontrol7.4PWMrectifiers7.1BasicprinciplesofPWMSimilarresponsetodifferentshapeofimpulseinputTheequal-areatheorem:

Responsestendtobeidenticalwheninputsignalshavesameareaandtimedurationsofinputimpulsesbecomeverysmall.BasicprinciplesofPWMApplicationoftheequal-areatheoremThisissinusoidalPWM(SPWM)Theequal-area

theoremcanbeappliedtorealizeanyshapeofwaveformsAlistofPWMtechniquesTriangular-wavesamplingNaturalsamplingUniformsamplingCalculationCalculationbasedonequal-areacriterionSelectiveharmonicseliminationHystereticcontrolSpaceVectorModulation(SVM,orSVPWM)RandomPWM7.2SomemajorPWMtechniquesNaturalsamplingUniformsamplingSelectiveharmonicseliminationSomepracticalissuesSynchronousmodulationandasynchronousmodulationHarmonicsinthePWMinverteroutputvoltagesWaystoimproveDCinputvoltageutilizationandreduceswitchingfrequencyConnectionofmultiplePWMinvertersTriangular-wavenaturalsamplingUni-polarPWMinsingle-phaseVSIUni-polarsamplingisusedto

realizeuni-polarPWM.Triangular-wavenaturalsamplingBi-polarPWMinsingle-phaseVSIBi-polarsamplingisusedto

realizebi-polarPWM.Triangular-wavenaturalsamplingIn3-phaseVSIThree-phasebridgeinvertercanonlyrealizebi-bolarPWMthereforeshouldbecontrolledbybipolarsampling.Triangular-waveuniformsamplingEasiertorealizebycomputer-controlModulationfactorSelectiveharmonicseliminationPWM(SHEPWM)

Frequencyrelationshipbetweentriangular-wavecarrierandcontrolsignalAsynchronousModulationSynchronousModulationHarmonicsinthePWMinverteroutputvoltagesNolowerorderharmonicsThelowestfrequencyharmonicsiswcandadjacentharmonics.wchasthehighestharmoniccontent.Spectrumof1-phase

bridgePWMinverter

outputvoltageHarmonicsinthePWMinverteroutputvoltagesNolowerorderharmonicsNoharmonicsatwc.Thelowestfrequencyandhighestcontentharmonicsarewc

2wrand2wc

wr.Spectrumof3-phasebridgePWMinverteroutputvoltageWaystoimproveutilizationofDCinputvoltageandreduceswitchingfrequencyUsetrapezoidalwaveformasmodulatingsignalinsteadofsinusoidalWaystoimproveutilizationofDCinputvoltageandreduceswitchingfrequencyUse3korderharmonicsbiasinthemodulatingsignalConnectionofmultiplePWMinvertersPurposesExpandoutputpowerratingReduceharmonicsSpaceVectorPWM(SVPWMorSVM)acbabbcca

abbcca[111]T

Phasevariables(a,bandc)produce line-to-linevariables(ab,bcandca)inplane-

Line-to-linevariables(ab,bcandca)donothave

-componentin-coordinatesystemVectorSpaceof3-phaseLine-to-LineVariablesLine-to-LineVoltageSpaceVectorwhereab

bcca

v

v

SpacevectorIfVmistheamplitudeofbalanced,symmetrical,three-phaseline-to-linevoltages,thenSwitchingStatesfor3-phaseVoltageSourceInverter

idcvabVdcsascsb010000000000011111111111icibib+ic0iaia+icia+ibia+ib+icSwitchingstatepnnppnnpnnppnnppnppppnnnvcavbcVdcVdcVdcVdcVdc-Vdc-Vdc-Vdc-Vdc-Vdc-Vdc000000000000iaibicvavcvbsasbscpnVdcidcSwitchingStateVector[pnn]ab,

bcca

v

v

SwitchingStateVector[ppn]ab,

bcca

v

SwitchingStateVector[ppp]ab,

bccaSwitchingStateVectors3015090-90-1500-3000

(°)SectorIIVIIIIIVVIatcenterpointab,

bcca

ReferenceVoltageVector,Vrefab,

bcca

v

v

whereIngeneral,

Assume

atcenterpointrefVrVref()V1()V2()T1T2T0TStTotalareaof=AreaofForexample

v

DefinitionofHighFrequencySynthesisSynthesisofVrefusingSwitchingStateVectorsab,

bcca

v

v

refVriaibicvavcvbsasbscpnVdcidcabc101010IIVIIIIIVVI

refVr

FromHFsynthesisdefinition,AssumeisconstantinTS,where

refVrDutyRatioofSwitchingStateVectorsinSVPWM7.3PWMtechniqueswith

feedbackcontrolCurrenthystereticcontrolVoltagehystereticcontrolTriangular-wavecomparison(sampling)withfeedbackcontrolCurrenthystereticcontrolInSingle-phaseVSICurrenthystereticcontrolIn3-phaseVSIVoltagehystereticcontrolTriangular-wavecomparison(sampling)withfeedbackcontrol