现代电力电子技术课件1chapter4-part 2

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1、4.4Forwardconverter•Buck-derivedtransformer-isolatedconverter•Single-transistorandtwo-transistorversions•Maximumdutycycleislimited•Transformerisresetwhiletransistorisoff1Forwardconverterwithtransformerequivalentcircuit2Forwardconverter:waveforms3Subinterval1:transistorconducts4Subinterval2:tran

2、sformerreset5Subinterval36Magnetizinginductancevolt-secondbalance7Transformerreset8WhathappenswhenD>0.59ConversionratioM(D)10Maximumdutycyclevs.transistorvoltagestressdecreasing11Flybackconverter12Derivationofflybackconverter13The“flybacktransformer”14Subinterval115Subinterval216CCMFlybackwavef

3、ormsandsolution17Discussion:Flybackconverter•Widelyusedinlowpowerand/orhighvoltageapplications•Lowpartscount•Multipleoutputsareeasilyobtained,withminimumadditionalparts•Crossregulationisinferiortobuck-derivedisolatedconverters•Oftenoperatedindiscontinuousconductionmode•DCManalysis:DCMbuck-boost

4、withturnsratio18Boost-derivedisolatedconvertersAwidevarietyofboost-derivedisolateddc-dconverterscanbederived,byinversionofsourceandloadofbuck-derivedisolatedconverters:•full-bridgeandhalf-bridgeisolatedboostconverters•inverseofforwardconverter:the“reverse”converter•push-pullboost-derivedconvert

5、erOfthese,thefull-bridgeandpush-pullboost-derivedisolatedconvertersarethemostpopular,andarebrieflydiscussedhere.19Full-bridgetransformer-isolatedboost-derivedconverter20Transformerresetmechanism21ConversionratioM(D)224.5ConverterevaluationanddesignForagivenapplication,whichconvertertopologyisbe

6、st?Thereisnoultimateconverter,perfectlysuitedforallpossibleapplications.Tradestudies.•Roughdesignsofseveralconvertertopologiestomeetthegivenspecifications.•Anunbiasedquantitativecomparisonofworst-casetransistorcurrentsandvoltages,transformersize,etc.Comparisonviaswitchstress,switchutilization,a

7、ndsemiconductorcost23Switchstressandswitchutilization•Largestsinglecostinaconverterisusuallythecostoftheactivesemiconductordevices•Conductionandswitchinglossesassociatedwiththeactivesemiconductordevicesoftendominatetheothersources