电力电子技术第5版 教学课件 作者 王兆安 chapter07.ppt

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1、PowerElectronicsChapter7PWMTechniquesThemostwidelyusedcontroltechniqueinpowerelectronicsPulseWidthModulation(PWM)(Choppingcontrol)DC/DCAC/ACDC/ACAC/DCOutline7.1Basicprinciples7.2SomemajorPWMtechniquesinDC/ACinverters7.3PWMtechniqueswithfeedbackcontrol7.4PWMrectifiers7.1BasicprinciplesofPWMSimilar

2、responsetodifferentshapeofimpulseinputTheequal-areatheorem:Responsestendtobeidenticalwheninputsignalshavesameareaandtimedurationsofinputimpulsesbecomeverysmall.BasicprinciplesofPWMApplicationoftheequal-areatheoremThisissinusoidalPWM(SPWM)Theequal-areatheoremcanbeappliedtorealizeanyshapeofwavefo

3、rmsAlistofPWMtechniquesTriangular-wavesamplingNaturalsamplingUniformsamplingCalculationCalculationbasedonequal-areacriterionSelectiveharmonicseliminationHystereticcontrolSpaceVectorModulation(SVM,orSVPWM)RandomPWM7.2SomemajorPWMtechniquesNaturalsamplingUniformsamplingSelectiveharmonicselimination

4、SomepracticalissuesSynchronousmodulationandasynchronousmodulationHarmonicsinthePWMinverteroutputvoltagesWaystoimproveDCinputvoltageutilizationandreduceswitchingfrequencyConnectionofmultiplePWMinvertersTriangular-wavenaturalsamplingUni-polarPWMinsingle-phaseVSIUni-polarsamplingisusedtorealizeuni-

5、polarPWM.Triangular-wavenaturalsamplingBi-polarPWMinsingle-phaseVSIBi-polarsamplingisusedtorealizebi-polarPWM.Triangular-wavenaturalsamplingIn3-phaseVSIThree-phasebridgeinvertercanonlyrealizebi-bolarPWMthereforeshouldbecontrolledbybipolarsampling.Triangular-waveuniformsamplingEasiertorealizebyco

6、mputer-controlModulationfactorSelectiveharmonicseliminationPWM(SHEPWM)Frequencyrelationshipbetweentriangular-wavecarrierandcontrolsignalAsynchronousModulationSynchronousModulationHarmonicsinthePWMinverteroutputvoltagesNolowerorderharmonicsThelowestfrequencyharmonicsiswcandadjacentharmonics.wchast

7、hehighestharmoniccontent.Spectrumof1-phasebridgePWMinverteroutputvoltageHarmonicsinthePWMinverteroutputvoltagesNolowerorderharmonicsNoharmonicsatwc.Thelowestfrequencyandhighestcontentharmonicsarewc2wrand2wcwr.Spect