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W功率因数校正开关电源的研究与设计外文翻译SWITCHINGPOWERSUPPLYDESIGN开关电源设计CHAPTER3HALFANDFULLBRIDGECONVERTERTOPOLOGIES31INTRODUCTIONHALFBRIDGEANDFULLBRIDGETOPOLOGIESSTRESSTHEIRTRANSISTORSTOAVOLTAGEEQUALTOTHEDCINPUTVOLTAGENOTTOTWICETHISVALUEASDOTHEPUSHPULLSINGLEENDEDANDINTERLEAVEDFORWARDCONVERTERTOPOLOGIESTHUSTHEBRIDGETOPOLOGIESAREUSEDMAINLYINOFFLINECONVERTERSWHERESUPPLYVOLTAGEWOULDBEMORETHANTHESWITCHINGTRANSISTORSCOULDSAFELYTOLERATEBRIDGETOPOLOGIESAREALMOSTALWAYSUSEDWHERETHENORMALACINPUTVOLTAGEIS220VORHIGHERANDFREQUENTLYEVENFOR120VACINPUTSANADDITIONALVALUABLEFEATUREOFTHEBRIDGETOPOLOGIESISTHATPRIMARYLEAKAGEINDUCTANCESPIKESFIGURES21AND210AREEASILYCLAMPEDTOTHEDCSUPPLYBUSANDTHEENERGYSTOREDINTHELEAKAGEINDUCTANCEISRETURNEDTOTHEINPUTINSTEADOFHAVINGTOBEDISSIPATEDINARESISTIVESNUBBERELEMENT32HALFBRIDGECONVERTERTOPOLOGY321BASICOPERATIONHALFBRIDGECONVERTERTOPOLOGYISSHOWNINFIGURE31ITSMAJORWADVANTAGEISTHATLIKETHEDOUBLEENDEDFORWARDCONVERTERITSUBJECTSTHE“OFF”TRANSISTORTOONLYVDCANDNOTTWICETHATVALUETHUSITISWIDELYUSEDINEQUIPMENTINTENDEDFORTHEEUROPEANMARKETWHERETHEACINPUTVOLTAGEIS220VFIRSTCONSIDERTHEINPUTRECTIFIERANDFILTERINFIGURE31ITISUSEDUNIVERSALLYWHENTHEEQUIPMENTISTOWORKFROMEITHER120VACAMERICANPOWEROR220VACEUROPEANPOWERTHECIRCUITALWAYSYIELDSROUGHLY320VRECTIFIEDDCVOLTAGEWHETHERTHEINPUTIS120ORFIGURE31HALFBRIDGECONVERTERONEENDOFTHEPOWERTRANSFORMERPRIMARYISCONNECTEDTOTHEWJUNCTIONOFFILTERCAPACITORSC1C2VIAASMALLDCLOCKINGCAPACITORCBTHEOTHERENDISCONNECTEDTOTHEJUNCTIONOFQ1Q2WHICHTURN“ON”AND“OFF”ONALTERNATEHALFCYCLESWITHS1INTHECLOSEDPOSITIONTHECIRCUITISAVOLTAGEDOUBLERINTHEOPENPOSITIONITISAFULLWAVERECTIFIERINEITHERCASETHERECTIFIEDOUTPUTISABOUT308TO336VDC220VACITDOESTHISWHENSWITCHS1ISSETTOTHEOPENPOSITIONFOR220VACINPUTORTOTHECLOSEDPOSITIONFOR120VACINPUTTHES1COMPONENTISNORMALLYNOTASWITCHMOREOFTENITISAWIRELINKTHATISEITHERINSTALLEDFOR120VACORNOTFOR220VACWITHTHESWITCHINTHEOPEN220VACPOSITIONTHECIRCUITISAFULLWAVERECTIFIERWITHFILTERCAPACITORSC1ANDC2INSERIESITPRODUCESAPEAKRECTIFIEDDCVOLTAGEOFABOUT1412202OR308VWHENTHESWITCHISINTHECLOSED120VACPOSITIONTHECIRCUITACTSASAVOLTAGEDOUBLERONEHALFCYCLEOFTHEINPUTVOLTAGEWHENAISPOSITIVERELATIVETOBC1ISCHARGEDPOSITIVELYVIAD1TOAPEAKOF1411201OR168VONAHALFCYCLEWHENAISNEGATIVEWITHRESPECTTOBCAPACITORC2ISCHARGEDPOSITIVELYVIAD2TO168VTHETOTALVOLTAGEACROSSC1ANDC2INSERIESISTHEN336VITCANBESEENINFIGURE31THATWITHEITHERTRANSISTOR“ON”THE“OFF”TRANSISTORISSUBJECTEDTOTHEMAXIMUMDCINPUTVOLTAGEANDNOTTWICETHATVALUESINCETHETOPOLOGYSUBJECTSTHE“OFF”TRANSISTORTOONLYVDCANDNOT2VDCTHEREAREMANYINEXPENSIVEBIPOLARANDMOSFETTRANSISTORSTHATCANSUPPORTTHENOMINAL336DCVPLUS15UPPERMAXIMUMOF386VTHUSTHEEQUIPMENTCANBEUSEDWITHEITHER120OR220VACLINEINPUTSBYMAKINGASIMPLESWITCHORLINKAGECHANGEASSUMINGANOMINALRECTIFIEDDCVOLTAGEOF336VTHETOPOLOGYWORKSASWFOLLOWSFORTHEMOMENTIGNORETHESMALLSERIESBLOCKINGCAPACITORCBASSUMETHEBOTTOMENDOFNPISCONNECTEDTOTHEJUNCTIONOFC1ANDC2THENIFTHELEAKAGESINC1C2AREASSUMEDTOBEEQUALTHATPOINTWILLBEATHALFTHERECTIFIEDDCVOLTAGEABOUT168VITISGENERALLYGOODPRACTICETOPLACEEQUALBLEEDERRESISTORSACROSSC1ANDC2TOEQUALIZETHEIRVOLTAGEDROPSNOWQ1ANDQ2CONDUCTONALTERNATEHALFCYCLESWHENQ1IS“ON”ANDQ2“OFF”FIGURE31THEDOTENDOFNPIS168VPOSITIVEWITHRESPECTTOITSNODOTENDANDTHE“OFF”STRESSONQ2ISONLY336VWHENQ2IS“ON”ANDQ1“OFF”THEDOTENDOFNPIS168VNEGATIVEWITHRESPECTTOITSNODOTENDANDTHEEMITTEROFQ1IS336VNEGATIVEWITHRESPECTTOITSCOLLECTORTHISACSQUAREWAVEPRIMARYVOLTAGEPRODUCESFULLWAVESQUAREWAVESHAPESONALLSECONDARIESEXACTLYLIKETHESECONDARYVOLTAGESINTHEPUSHPULLTOPOLOGYTHESELECTIONOFSECONDARYVOLTAGESANDWIRESIZESANDTHEOUTPUTINDUCTORANDCAPACITORPROCEEDEXACTLYASFORTHEPUSHPULLCIRCUIT322HALFBRIDGEMAGNETICS3221SELECTINGMAXIMUM“ON”TIMEMAGNETICCOREANDPRIMARYTURNSITCANBESEENINFIGURE31THATIFQ1ANDQ2ARE“ON”SIMULTANEOUSLYEVENFORAVERYSHORTTIMETHEREISASHORTCIRCUITACROSSTHESUPPLYVOLTAGEANDTHETRANSISTORSWILLBEDESTROYEDTOMAKESURETHATTHISDOESNOTHAPPENTHEMAXIMUMQ1ORQ2“ON”TIMEWHICHOCCURSATMINIMUMDCSUPPLYVOLTAGEWILLBESETAT80OFAHALFPERIODTHESECONDARYTURNSWILLBECHOSENSOTHATWTHEDESIREDOUTPUTVOLTAGESAREOBTAINEDWITHAN“ON”TIMEOFNOMORETHAN08T/2AN“ON”TIMECLAMPWILLBEPROVIDEDTOENSURETHATTHE“ON”TIMECANNEVERBEGREATERTHAN08T/2UNDERFAULTORTRANSIENTCONDITIONSTHECOREISSELECTEDFROMTHETABLESINCHAPTER7MENTIONEDEARLIERTHESETABLESGIVEMAXIMUMAVAILABLEOUTPUTPOWERASAFUNCTIONOFOPERATINGFREQUENCYPEAKFLUXDENSITYCOREANDIRONAREASANDCOILCURRENTDENSITYWITHACORESELECTEDANDITSIRONAREAKNOWNTHENUMBEROFPRIMARYTURNSISCALCULATEDFROMFARADAYSLAWEQ117USINGTHEMINIMUMPRIMARYVOLTAGEVDC/21ANDTHEMAXIMUM“ON”TIMEOF08T/2HERETHEFLUXEXCURSIONDBINTHEEQUATIONISTWICETHEDESIREDPEAKFLUXDENSITY1600GBELOW50KHZORLESSATHIGHERFREQUENCYBECAUSETHEHALFBRIDGECOREOPERATESINTHEFIRSTANDTHIRDQUADRANTSOFITSHYSTERESISLOOPUNLIKETHEFORWARDCONVERTERSECTION239WHICHOPERATESINTHEFIRSTQUADRANTONLY3222THERELATIONBETWEENINPUTVOLTAGEPRIMARYCURRENTANDOUTPUTPOWERIFWEASSUMEANEFFICIENCYOF80THENPIN125POTHEINPUTPOWERATMINIMUMSUPPLYVOLTAGEISTHEPRODUCTOFMINIMUMPRIMARYVOLTAGEANDAVERAGEPRIMARYCURRENTATMINIMUMDCINPUTATMINIMUMDCINPUTTHEMAXIMUM“ON”TIMEINEACHHALFPERIODWILLBESETAT08T/2ASDISCUSSEDABOVEANDTHEPRIMARYHASTWOCURRENTPULSESOFWIDTHW08T/2PERPERIODTATPRIMARYVOLTAGEVDC/2THEINPUTPOWERIS125POVDC/2IPFT08T/TWHEREIPFTISTHEPEAKEQUIVALENTFLATTOPPEDPRIMARYCURRENTPULSETHENIPFTHALFBRIDGE313P0/VDC313223PRIMARYWIRESIZESELECTIONPRIMARYWIRESIZEMUSTBEMUCHLARGERINAHALFBRIDGETHANINAPUSHPULLCIRCUITOFTHESAMEOUTPUTPOWERHOWEVERTHEREARETWOHALFPRIMARIESINTHEPUSHPULLEACHOFWHICHHASTOSUPPORTTWICETHEVOLTAGEOFTHEHALFBRIDGEPRIMARYWHENOPERATEDFROMTHESAMESUPPLYVOLTAGECONSEQUENTLYCOILSIZESFORTHETWOTOPOLOGIESARENOTMUCHDIFFERENTHALFBRIDGEPRIMARYRMSCURRENTISIRMSIPFTANDFROMEQ31IRMS279PO/VDC32AT500CIRCULARMILSPERRMSAMPERETHEREQUIREDNUMBEROFCIRCULARMILSISCIRCULARMILSNEEDED500279PO/VDC1395PO/VDC333224SECONDARYTURNSANDWIRESIZESELECTIONINTHEFOLLOWINGTREATMENTTHENUMBEROFSECONDARYTURNSWILLBESELECTEDUSINGEQS21TO23FORTON08T/2ANDTHETERMVDC1WILLBEREPLACEDBYTHEMINIMUMPRIMARYVOLTAGEWHICHISVDC/21THESECONDARYRMSWCURRENTSANDWIRESIZESARECALCULATEDFROMEQS213AND214EXACTLYASFORTHEFULLWAVESECONDARIESOFAPUSHPULLCIRCUIT323OUTPUTFILTERCALCULATIONSTHEOUTPUTINDUCTORANDCAPACITORARESELECTEDUSINGEQS220AND222ASINAPUSHPULLCIRCUITFORTHESAMEINDUCTORCURRENTRAMPAMPLITUDEANDDESIREDOUTPUTRIPPLEVOLTAGE324BLOCKINGCAPACITORTOAVOIDFLUXIMBALANCETOAVOIDTHEFLUXIMBALANCEPROBLEMDISCUSSEDINCONNECTIONWITHTHEPUSHPULLCIRCUITSECTION225ASMALLCAPACITORCBISFITTEDINSERIESWITHTHEPRIMARYASINFIGURE31RECALLTHATFLUXIMBALANCEOCCURSIFTHEVOLTSECONDPRODUCTACROSSTHEPRIMARYWHILETHECOREISSETMOVESINONEDIRECTIONALONGTHEHYSTERESISLOOPDIFFERSFROMTHEVOLTSECONDPRODUCTAFTERITMOVESINTHEOPPOSITEDIRECTIONTHUSIFTHEJUNCTIONOFC1ANDC2ISNOTATEXACTLYHALFTHESUPPLYVOLTAGETHEVOLTAGEACROSSTHEPRIMARYWHENQ1IS“ON”WILLDIFFERFROMTHEVOLTAGEACROSSITWHENQ2IS“ON”ANDTHECOREWILLWALKUPORDOWNTHEHYSTERESISLOOPEVENTUALLYCAUSINGSATURATIONANDDESTROYINGTHETRANSISTORSTHISSATURATINGEFFECTCOMESABOUTBECAUSETHEREISANEFFECTIVEDCCURRENTBIASINTHEPRIMARYTOAVOIDTHISDCBIASTHEBLOCKINGCAPACITORISPLACEDINSERIESINTHEPRIMARYTHECAPACITORVALUEISSELECTEDWFIGURE32THESMALLBLOCKINGCAPACITORCBINSERIESWITHTHEHALFBRIDGEPRIMARYFIGURE31ISNEEDEDTOPREVENTFLUXIMBALANCEIFTHEJUNCTIONOFTHEFILTERCAPACITORSISNOTATEXACTLYTHEMIDPOINTOFTHESUPPLYVOLTAGEPRIMARYCURRENTCHARGESTHECAPACITORCAUSINGADROOPINTHEPRIMARYVOLTAGEWAVEFORMTHISDROOPSHOULDBEKEPTTONOMORETHAN10THEDROOPINPRIMARYVOLTAGEDUETOTHEOFFSETCHARGINGOFTHEBLOCKINGCAPACITORISSHOWNASDVASFOLLOWSTHECAPACITORCHARGESUPASTHEPRIMARYCURRENTIPFTFLOWSINTOITROBBINGVOLTAGEFROMTHEFLATTOPPEDPRIMARYPULSESHOWNINFIGURE32THISDCOFFSETROBSVOLTSECONDSFROMALLSECONDARYWINDINGSANDFORCESALONGER“ON”TIMETOACHIEVETHEDESIREDOUTPUTVOLTAGEINGENERALITISDESIRABLETOKEEPTHEPRIMARYVOLTAGEPULSESASFLATTOPPEDASPOSSIBLEINTHISEXAMPLEWEWILLASSUMEAPERMISSIBLEDROOPOFDVTHEEQUIVALENTFLATTOPPEDCURRENTPULSETHATCAUSESTHISDROOPISIPFTINEQ31THENBECAUSETHATCURRENTFLOWSFOR08T/2THEREQUIREDCAPACITORMAGNITUDEISSIMPLYCB34CONSIDERANEXAMPLEASSUMINGA150WHALFBRIDGEOPERATINGAT100KHZFROMANOMINALDCINPUTOF320VAT15LOWLINETHEDCINPUTIS272VANDTHEPRIMARYVOLTAGEIS272/2OR136VATOLERABLEDROOPINTHEFLATTOPPEDPRIMARYVOLTAGEPULSEWOULDWBE10ORABOUT14VTHENFROMEQ31FOR150WANDVDCOF272VIPFT313150/272173AANDFROMEQ34CB173085106/14049FTHECAPACITORMUSTBEANONPOLARIZEDTYPE325HALFBRIDGELEAKAGEINDUCTANCEPROBLEMSLEAKAGEINDUCTANCESPIKESWHICHARESOTROUBLESOMEINTHESINGLEENDEDFORWARDCONVERTERANDPUSHPULLTOPOLOGYAREEASILYAVOIDEDINTHEHALFBRIDGETHEYARECLAMPEDTOVDCBYTHECLAMPINGDIODESD5D6ACROSSTRANSISTORSQ1Q2ASSUMINGQ1IS“ON”THELOADANDMAGNETIZINGCURRENTSFLOWTHROUGHITANDTHROUGHTHEPRIMARYLEAKAGEINDUCTANCEOFT1THEPARALLELEDT1MAGNETIZINGINDUCTANCEANDTHESECONDARYLOADIMPEDANCESTHATAREREFLECTEDBYTHEIRTURNRATIOSSQUAREDINTOTHEPRIMARYTHENITFLOWSTHROUGHCBINTOTHEC1C2JUNCTIONTHEDOTENDOFNPISPOSITIVEWITHRESPECTTOITSNODOTENDWHENQ1TURNS“OFF”THEMAGNETIZINGINDUCTANCEFORCESALLWINDINGPOLARITIESTOREVERSETHEDOTENDOFT1STARTSTOGONEGATIVEBYFLYBACKACTIONANDIFTHISWERETOCONTINUEITWOULDPUTMORETHANVDCACROSSQ1ANDCOULDDAMAGEITALSOQ2COULDBEDAMAGEDBYIMPOSINGAREVERSEVOLTAGEACROSSITHOWEVERTHEDOTENDOFT1ISCLAMPEDBYDIODED6TOTHESUPPLYRAILVDCANDCANGONOMORENEGATIVETHANTHENEGATIVEENDOFTHESUPPLYSIMILARLYWHENQ2IS“ON”ITSTORESCURRENTINTHEMAGNETIZINGWINDUCTANCEANDTHEDOTENDOFNPISNEGATIVEWITHRESPECTTOTHENODOTENDWHICHISCLOSETOVDC/2WHENQ2TURNS“OFF”THEMAGNETIZINGINDUCTANCEREVERSESALLWINDINGPOLARITIESBYFLYBACKACTIONANDTHEDOTENDOFNPTRIESTOGOPOSITIVEBUTISCAUGHTATVDCBYCLAMPDIODED5THUSTHEENERGYSTOREDINTHELEAKAGEINDUCTANCEDURINGTHE“ON”TIMEISRETURNEDTOTHESUPPLYRAILVDCVIADIODESD5D6译文第三章半桥和全桥变换器拓扑31概述半桥和全桥拓扑开关管的稳态关断电压等于直流输入电压,而不像推挽、单端正激或交错正激拓扑那样为电压的两倍。所以桥式拓扑广泛用于直接电网的离线式变换器。而对推挽等拓扑来说,两倍的电网整流电压将超过其开关管的安全耐压容限。为此,输入网压为220V或更高的场合几乎都使用桥式拓扑。当输入网压为120V时也有使用桥式拓扑的情况。桥式拓扑的另一优点是,能将变压器初级侧的漏感尖峰电压(如图21和图210所示)箝位于直流母线电压,并将漏感储存的能量归还到输入母线,而不是消耗于电阻元件。32半桥变换器拓扑321工作原理半桥变换器拓扑结构如图31所示。其主要优点是,开关管关断时承受电压为VDC(与双端正激变换器相同),而不是像推挽拓扑或是单端正激变换器那样为2VDC。因此,该拓扑在网压为220V的欧洲市场设备中得到W广泛应用。首先看图31中的输入整流和滤波部分。当要求设备适应不同的网压(120VAC(美国)或220VAC欧洲)时,这是一种普遍采用的方案。不管输入网压是120VAC还是220VAC,该电路整流得到的直流电压均为320V。当输入网压为220VAC时,S1断开;为120VAC时,S1闭合。事实上S1并不是实际的开关,而是一个根据不同输入而闭合或断开的接点。S1断开时,输入为220V交流电压,电路为全波整流电路,滤波电容C1和C2串联,整流得到的直流电压峰值约为141X2202308V;当S1闭合时,输入为120V交流电压,电路相当于一个倍压整流器。在输入电压的正半周,A点相对于B点为正,电源鼶1给C1充电,C1电压为上正下负,
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