缓冲电路参数选取课件.ppt

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1、Chapter27：SnubberCircuits27-1FunctionandTypesofsnubberCircuits27-2DiodesSnubber27-3SnubberCircuitsforThyristors27-4NeedforSnubberswithTransistors27-5Turn-offSnubber27-6Overvoltagesnubber27-7Turn-onSnubber27-8SnubbersforBridgeCircuitConfigurations27-9GTOSnubberConsiderations27-1OverviewofSnubberC

2、ircuitsforHard-SwitchedConvertersFunction:Protectsemiconductordevicesby:Limitingdevicevoltagesduringturn-offtransientsLimitingdevicecurrentsduringturn-ontransientsLimitingtherate-of-rise(di/dt)ofcurrentsthroughthesemiconductordeviceatdeviceturn-onLimitingtherate-of-rise(dv/dt)ofvoltagesacrossthe

3、semiconductordeviceatdeviceturn-offShapingtheswitchingtrajectoryofthedeviceasitturnson/offTypesofSnubberCircuits1.UnpolarizedseriesR-Csnubbers•Usedtoprotectdiodesandthyristors2.PolarizedR-Csnubbers•Usedasturn-offsnubberstoshapetheturn-offswitchingtrajectoryofcontrolledswitches.•Usedasovervoltage

4、snubberstoclampvoltagesappliedtocontrolledswitchestosafevalues.•Limitdv/dtduringdeviceturn-off3.PolarizedL-Rsnubbers•Usedasturn-onsnubberstoshapetheturn-onswitchingtrajectoryofcontrolledswitches.•Limitdi/dtduringdeviceturn-on27-2NeedforDiodeSnubberCircuit1ThecauseofovervoltagesTheovervoltagesocc

5、urduetothestrayorleakageinductanceLσinserieswiththediodeandthesnap-offofthediodereverserecoverycurrent.-+DfRsCsLsVdIoSwIrrdtVdLs=IottiDf(t)DiodevoltagewithoutsnubberdtLsdiLsvDf(t)diDfVd27-2NeedforDiodeSnubberCircuit2overvoltageprotectionIntroducingaRs-CssnubbercircuitIntroducingabaselinecapacita

6、nceCbaseandbaselineresistanceRbase,-+DfRsCsLsVdIoSw3PerformanceofR-CSnubberVmax=themaximumreversevoltageacrossthediode.ThereisanoptimumvalueofRs=Ropt=1.3RbasethatminimizesVmax.0123012VdVmaxRsRbaseRsIrrVdCs=CbaseRs,optRbase=1.34Implementation(2)Step-down,half-bridgeandfull-bridgeconvertersmaynotr

7、equireadiodesnubberifLσisminimizedbypropercircuitlayout.(1)Theconvertersthoseconsistofanisolationtransformerthatintroducedasubstantialleakageinductanceneeddiodesnubbercircuits.(3)Sinle-phaseline-frequencydiodeconverters.+Vs-