功率半导体器件的原理与应用（英文版）

0Operationprincipleofpowersemiconductors10Operationprincipleofpowersemiconductors0.1BasicswitchingprocessesApartfromafewspecialapplications,powersemiconductorsaremainlyusedinswitchingapplications.Thisleadstosomebasicprinciplesandoperationmodeswhichapplytoallpowerelectronicscircuitries.Themostimportantgoalofalleffortsindevelopingtheproductrangeofpowersemiconductorsandtheirapplicationsincircuitsistoreachminimumpowerlosses.Limitconditionsfortheidealswitcharecharacterizedasfollows:idealswitch-On-state:vs=0;-∞is∞-Off-state:is=0;-∞vs∞-Switchingbehaviour:noconversionofenergyduringactiveturn-on/turn-offTheapplicationofsuchidealswitchesand,consequently,theuseofpowersemiconductorsisthereforesubjecttorestrictiveswitchingconditions.Switchesininductivecircuits(impressedcurrent)Aswitchappliedinaninductivecircuit(Fig.0.1)canactivelybeturnedon,i.e.itcanbeturnedonatanytime.Thereisnopowerlossundertheconditionofinfiniteswitchingtime,sincethebiasvoltagemaydropdirectlyoverthelineinductance.Ifthecircuitislive,turn-offisnotpossiblewithoutconversionofenergy,sincetheenergystoredinLhastobeconverted.Forthisreason,turn-offoftheswitchwithoutanyenergyconversionisonlypossibleifis=0.Thisisalsocalledpassiveturn-off,sincetheswitchingmomentisdependentonthecurrentflowinthecircuit.Aswitchthatisrunningundertheseswitchingconditionsiscalledzero-current-switch(ZCS).-On-state:vs=0;-∞is∞-Off-state:is=0;-∞vs∞-Switchingbehaviour:activeturn-onat|vs|0passiveturn-offatis=0LissvFigure0.1Switchinaninductivecircuit0Operationprincipleofpowersemiconductors2Switchbetweencapacitivenodes(impressedvoltage)Nondissipativeturn-onofaswitchunderaimpressedvoltageisonlypossibleifvs=0.Thisiscalledpassiveturn-on,sincethevoltagewaveformand,thus,thezerocrossingisdeterminedbytheoutercircuit.Activeturn-off,however,willbepossibleatanytime.Switchesrunningunderthoseswitchingconditionsarecalledzero-voltage-switches(ZVS).-On-state:vs=0;-∞is∞-Off-state:is=0;-∞vs∞-Switchingbehaviour:activeturn-offat|is|0passiveturn-onatvs=0Figure0.3showscurrentandvoltagewaveformsduringthebasicswitchingprocessesdescribedabove.Theuseofrealpowersemiconductorsasswitcheswillleadtothefollowingconditions.Beforeactiveturn-on,thecurrent-transferringsemiconductorisunderpositivevoltage.Voltagemaydrop,if,triggeredbythecontroller,thecurrentincreasesbyacertainrategivenbytheturn-onmechanismofthepowersemiconductor.Thisturn-onmechanismtogetherwiththeseriesinductanceislimitingthecurrentriseandvoltagedistributionwithinthecircuitbetweenpowersemiconductorandinductance.Turn-onpowerlossesofthegivenpowersemiconductorarediminishedtoaminimumvaluebyincreaseofinductance.Duringpassiveturn-offofalivepowersemiconductorcarryingcurrentinpositivedirection,currentdropstozeroduetothevoltagepolarityoftheoutercircuit.Currentisconductedbackasreversecurrentbythechargecarriersstillstoredinthesemiconductoruntilthesemiconductorhasrecovereditsblockingcapabilitytotakeupthenegativecircuitvoltage.Activeturn-offofalivepowersemiconductorwill,firstofall,produceavoltageriseinpositivedirectiontriggeredbythecontroller.Then,theeffectiveparallelcapacitancewilltakeoverthecurrentflowgivenbytheturn-offmechanismofthepowersemiconductor.Theenergylosscausedbytheturn-offprocedureisreducedbytheincreaseofcapacitanceforthegivenpowersemiconductor.Apassivelyswitchedpowersemiconductorisundernegativevoltagebeforeturn-on.Ifthisvoltagechangespolarityduetoprocessesintheoutercircuit,thepowersemiconductorwilltakeupcurrentinpositivedirection,whichwillleadtoturn-onovervoltageincaseofimpressedcurrentrise.issuFigure0.2Switchbetweencapacitivenodes0Operationprincipleofpowersemiconductors3activeONSwitchingProcessWaveformEquivalentCircuitpassiveOFFactiveOFFpassiveONBasicSwitchingProcessesdiSV0dtdS0dtdiSV0dtdS0dt;;diSV0dtd0dt;dSdt;diV0dtdS0dt;SVSVqiSiSVqiSSVSVSViSqiSViSqiqiiSiSiSSVSVSVVqqVVq0Vq0Figure0.3BasicswitchingprocessesEverypowerelectronicsystemworksaccordingtotwobasicfunctionprinciples:•firstly,turn-onandturn-offofconnectionleadsbetweenenergyexchangingcircuitriesbymeansofoneswitcheach-calledcyclicswitchingofsingleswitchesand•secondly,alternatingswitchingoftwoswitcheseach,alternatingcurrent-andvoltage-carrying-calledcommutation.Bothbasicprinciplesmaybeintegratedintoonecircuitandthecircuitsplitintoseveraldifferentoperationmodes.0Operationprincipleofpowersemiconductors40.2OperationprincipleofpowersemiconductorsTheoperationprincipleofpowersemiconductorsisclearlydefinedinthepreviouslyexplainedactiveandpassiveswitchingproceduresduringcyclicswitchingofsingleswitchesandinductiveorcapacitivecommutation.Figure0.4showsasummaryoftherelationshipsbetweencurrentandvoltageduringthedifferentpossibleswitchingprocedures.Hardswitching(HS,Figure0.7)Hardturn-onischaracterizedbyanalmosttotalvKvoltagedropoverthecurrent-carryingswitchS1atacurrentcommutationtimetKcausingconsiderablepowerlosspeakswithinthepowersemiconductor.Commutationinductanceisatitsminimumvalueatthatmoment,i.e.theturnedonsemiconductordeterminesthecurrentincrease.Currentcommutationisterminatedbypassiveturn-o