电力电子技术第5版 教学课件 作者 王兆安 chapter05.ppt

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1、PowerElectronicsChapter5DCtoDCConverters(Choppers)Outline5.1BasicDCtoDCconverters5.2CompositeDC/DCconvertersandconnectionofmultipleDC/DCconverters5.3IsolatedDCtoDCconverters(IndirectDCtoDCconverters)5.1BasicDCtoDCconverters5.1.1Buckconverter(Step-downconverter)5.1.2Boostconverter(Step-upconvert

2、er)5.1.3Buck-Boostconverter(Step-down/step-upconverter)andCukconverter5.1.4SepicconverterandZetaconverter5.1BasicDCtoDCconvertersIntroduction—BuckconverterSPDTswitchchangesdccomponentSwitchoutputvoltagewaveformDutycycleD:0£D£1complementD’:D’=1-DDccomponentofswitchoutputvoltageFourieranalysis:

3、Dccomponent=averagevalueInsertionoflow-passfiltertoremoveswitchingharmonicsandpassonlydccomponentBasicoperationprincipleofbuckconverterBuckconverterwithidealswitchRealizationusingpowerMOSFETanddiodeThoughtprocessinanalyzingbasicDC/DCconvertersBasicoperationprinciple(qualitativeanalysis)Howdoesc

4、urrentflowduringdifferentswitchingstatesHowisenergytransferredduringdifferentswitchingstatesVerificationofsmallrippleapproximationDerivationofinductorvoltagewaveformduringdifferentswitchingstatesQuantitativeanalysisaccordingtoinductorvolt-secondbalanceorcapacitorchargebalanceActualoutputvoltage

5、waveformofbuckconverterBuckconvertercontainingpracticallow-passfilterActualoutputvoltagewaveformv(t)=V+vripple(t)Thesmallrippleapproximationv(t)=V+vripple(t)Inawell-designedconverter,theoutputvoltagerippleissmall.Hence,thewaveformscanbeeasilydeterminedbyignoringtheripple:Buckconverteranalys

6、is:inductorcurrentwaveformInductorvoltageandcurrentsubinterval1:switchinposition1Inductorvoltageandcurrentsubinterval2:switchinposition2InductorvoltageandcurrentwaveformsDeterminationofinductorcurrentripplemagnitudeInductorcurrentwaveformduringstart-uptransientTheprincipleofinductorvolt-sec

7、ondbalance:DerivationInductorvolt-secondbalance:BuckconverterexampleTheprincipleofcapacitorchargebalance:DerivationBoostconverterexampleBoostconverteranalysisSubinterval1:switchinposition1Subinterval2:switchinposition2Inductorvol