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ID:57159767
大小:5.12 MB
页数:91页
时间:2020-08-02
《电力电子技术课程-软开关课件.ppt》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、第七章软开关谐振功率变换技术徐德鸿浙江大学从提问开始什么是软开关技术(softswitching)?为什么要使用softswitching?如何实现softswitching?软开关的概念Conceptofsoftswitching理想开关(Idealswitch)Dynamic characteristicsTurnontime=0Turnofftime=0StaticcharacteristicsONstateR=0OffstateR=infiniteVdsIdsAKG寄生参数(Parasiticcapacitance)PowerM
2、OSFETDiodeLayoutstraycapacitance(寄生/参杂电容)Transformerwindingcapacitance二极管反向恢复过程(Diodereverserecovery)Highdi/dt,EMIproblemHighlossonswitchanddiodeInthefutureSiCSchottkydiode反向恢复过程引起的损耗(Switchinglossresultingfromreverserecovery)Reverserecoverychargevs.Turn-onlossinswitchandF
3、red寄生电感(Parasiticinductance)LeakageinductanceofthetransformerStrayinductanceLayoutWirebondsindevicepackagesLeadsofdevices理想的元件构成的BUCK变换器(IdealBuckconverter)SquareWaveformsNoSwitchingLossParasiticOscillationsSwitchingLossSnubberLossGate-DriveMillerEffectLowEfficiencyatHF实际元
4、件构成的BUCK变换器(PracticalBUCKconverter)IdealPractice理想反激变换器(idealflybackconverter)TransformerMOSFETSchottkyDiode实际的反激变换器(Flybackconverterwithparasitic)SwitchonstageSwitchoffstage@assumethatmagnetizinginductanceisverylarge实际的反激变换器的阶段等效电路ExperimentWaveformPWMflybackconverterVds吸
5、收电路(PrimaryswitchRCsnubber)并联谐振电路(RLCparallelresonancecircuit)Dampingcondition:吸收电路(Rectifiersnubber)电压钳位(Voltageclamp)吸收电路(PrimaryswitchRCDsnubber)吸收电路的优化(RCDsnubberoptimization)Powerdissipation开关损耗(Hardswitchingoperation)开关频率开关损耗(Switchingloss)平均开关损耗功率与开关频率和重叠时间之积成正比。因此在
6、高频应用场合为抑制开关损耗,需选用开关速度快的器件减少重叠时间(Reduceoverlappingtime)Averagedswitchingloss:Switchingoverlappingtime开关损耗与重叠时间关系(Switchinglossreductionratio)Present/Originalloss:电压应力(VoltageSurge)VoltagestressofMOSFETwhenitturnsoff:电流应力(CurrentSurge)MOSFETsurgecurrentwhenturnon:HigherHighe
7、rShorterBecomelarger电应力(Voltageandcurrentsurges)软开关的分类(Typesofsoftswitching)Cutdownturn-onloss:ZCSonZVSonCutdownturn-offloss:ZCSoffZVSoff零电流开通Zerocurrentswitchon(ZCSon)TurnonwithzerocurrentOverlaptimestillexistButintegralofmultiplicationofudsandidsisreducedTurn-onswitching
8、lossisreduced零电压开通Zerovoltageswitchon(ZVSon)TurnonwithzerovoltageOverlaptimeiszerointegra
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