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1、7.3Typicalsoft-switchingcircuitsandtechniquesSincethesoft-switchingtechniquesappears,ithasbeendevelopedandimprovedconstantly.Therearestillmanykindsofsoft-switchingtechniquesappearing.Aseachkindofsoft-switchingcircuithasitsowncharacteristicandapplication,soitisverynecessarytoclassifythesesof
2、t-switchingcircuits.Therearesometypicalsoft-switchingcircuitsandsometechniquesinpowerelectronics,suchasZVSQRC,ZCSQRC,ZVSMRC,phase-shiftbriageZVSPWMconvert,ZVTPWMconvertandsoon.Zero-Voltage-SwitchingQuasi-ResonantConvertter(ZVSQRC)ZVSQRCisasimplesoft-switchingcircuits.Fig.7-3-1showsthecircui
3、tprincipleofZVSZQC,andFig7-3-2showstheidealwaveformofZVSZQC.Intheprocessofouranalysis,wesupposetheinductorLandthecapacitorCisverylarge,andweignorethelossinthecircuit.ItissuitableFig.7-3-2TheidealwaveformofZVSQRCFig.7-3-1ThecircuitprincipleofZVSQRCtochoosethetimeoftheswitchSturnedoffasthesta
4、rtingpointofour8analysis.NowweanalysetheworkingprocessofZVSQRCwithFig.7-3-2.Fromt0tot1,theswitchsisoff,andthecapacitorCrmakesthevoltageincreaseslowly.Atthesametme,thediodeVDisstilloff.BecurseofthelargeL,uCrincreaseslinearly,anditsincreaserateduCrdt=ILCrFromt1tot2,thediodeVDison,souCrkeepson
5、increaseingandiLrcomesdowntillthetimet2,anduCrgetsthetop;Fig.7-3-4Theaquivalentcircuitfromt1tot2Fig.7-3-3Theaquivalentcircuitfromt0tot1Fromt2tot3,iLrchangesthedirection,anduCrkeepsondecreaseinguntilthetimet3.Atthetime,uCr=Ui,andiLrgetsthereversetop;Fromt3tot4,LRchargestoCRatthereversedirect
6、ion.uCrkeepsondecreaseinguntilthetimet4,andatthistimeuCr=0;LrdiLrdt+uCr=UiCrduCrdt=iLruCrt=t1=Ui,iLrt=t1=ILFromt4tot5,iLrdecreaseslinearlyuntilthetimet5,iLr=0;Fromt5tot6,theswitchSison,andiLrincreaseslinearlyuntilthe8timet6,iLr=IL.ThenthediodeVDbecomesoff.ThechangingrateofiLrisdiLrdt=UiLrFr
7、omt6tot0,theswitchSison,andthediodeVDisoff.TherearesomedisadvantagesofZVSQRC,likethevoltagestressincreasedduetotheresonantpeak,currentRMSvalueincreasedduetolargecirculaingenergy,andvariableswitchingfrequencyduetopulse-frequencymodulationcontrol.ResonantD
