《新能源汽车驱动电机系统检修》课件-认知DC-DC变换电路-英文

RecognizeDC-DCconversioncircuitsADC-DCconverter,alsoknownasaDCchopper,isapowerelectronicconverterdevicethatconvertsDCwithaconstantvoltageintoDCwithadjustablevoltage.ThebasicideaofDCconversionwithDC-DCconverteristocuttheconstantDCvoltageorcurrentintoaseriesofpulsevoltagesorcurrentsthroughtheon-onandturn-offcontrolofthepowerswitchingdevice,andundercertainfilteringconditions,theaveragevalueofthevoltageorcurrentontheloadcanbelessthanorgreaterthanthatofthepowersupply.TheactualDC-DCconverterisshowninFigure1Figure1TheactualDC-DCconverter1.OverviewofDC-DCconverters

ThemostbasicDCchoppercircuitisshowninFigure2(a),whereSisacontrollableswitchandRisapurelyresistiveload.WhenSisclosed,theoutputvoltageisE;WhenSisturnedoff,theoutputvoltageis0andtheoutputwaveformisshowninFigure2(b).Figure2:HowaDC-DCconverterworksAssumingthattheon-offperiodoftheswitchSisunchanged,theratiooftheon-timeofStotheswitchingperiodisdefinedasthedutycycle,whichisdenotedbyD.Thedutycyclecanbechangedbychangingtheon-timeorturn-offtime.Generally,therearethreemaincontrolmethodsforDCchoppercircuits.1.PulsefrequencymodulationcontrolmodeInthiscontrolmode,becausetheperiodorfrequencyoftheoutputvoltagewaveformischanging,thefrequencyoftheoutputharmonicisalsochanging,whichmakesthedesignofthefiltermoredifficult,andtheharmonicinterferenceoftheoutputwaveformisserious,anditisgenerallyrarelyused.2.theworkingprincipleofDC-DCconverter

ThemostbasicDCchoppercircuitisshowninFigure2(a),whereSisacontrollableswitchandRisapurelyresistiveload.WhenSisclosed,theoutputvoltageisE;WhenSisturnedoff,theoutputvoltageis0andtheoutputwaveformisshowninFigure2(b).Figure2:HowaDC-DCconverterworks2.PulsewidthmodulationcontrolmodeInthiscontrolmethod,theperiodorfrequencyoftheoutputvoltagewaveformisconstant,andthereforethefrequencyoftheoutputharmonicsisalsoconstant,whichmakesthedesignofthefiltereasierandisthereforewidelyused.3.FrequencymodulationandwidthmodulationhybridcontrolmodeThiscontrolmethodcangreatlyincreasetherangeoftheoutput,butbecausethefrequencyisvariable,thereisalsotheproblemthatitisdifficulttodesignthefilter.2.theworkingprincipleofDC-DCconverter

Abuckchoppercircuit,alsoknownasabuckchoppercircuit,ischaracterizedbyaloweroutputvoltagethantheinputvoltageandahigheroutputcurrentthantheinputcurrent.Thatistosay,throughtheconversionofthiscircuit,theDCpowersupplyvoltagecanbeconvertedtotheDCvoltagebelowitsvalue,andtheconversionofelectricenergycanberealized.ThetopologyofthebuckchoppercircuitisshowninFigure3(a).Sinthefigureisaswitchingdevice,anddifferentpowerelectronicdevicescanbeselectedaccordingtotheapplicationneeds,suchasIGBT,MOSFET,GTR,etc.LandCarethefilterinductorsandcapacitors,whichformalow-passfilter,Ristheload,andVDisthefreewheelingdiode.WhentheSisdisconnected,theVDprovidesafreewheelingpath.EistheinputDCvoltage.WhenanIGBTisselectedasaswitchingdevice,thecircuitdiagramisshowninFigure3(b).Figure3Step-downchoppercircuit3.Step-downchoppercircuit

Theboostchoppercircuit,alsoknownastheboostchoppercircuit,isusedtoconverttheDCpowersupplyvoltageintoaDCoutputvoltagehigherthanitsvalue,soastorealizethetransferofenergyfromthelow-voltagesidepowersupplytothehigh-voltagesideload.Figure4showsthetopologyofaDC-DCstep-upchoppercircuitusinganIGBTasaswitchingdevice.Figure4Step-upchoppercircuitWhenanalyzingtheoperatingprincipleofastep-upchoppercircuit,itshouldbeassumedthattheinductanceLinthecircuitislarge,andthecapacitanceCisalsolarge.WhenVTisturnedon,thepowersupplyEchargestheinductorL,andthechargingcurrentisbasicallyconstant,andthevoltageonthecapacitorCsuppliespowertotheloadR,becausetheCvalueislarge,sotheoutputvoltagecanbebasicallykeptasconstantvalue.Therearetworeasonswhytheboostchoppercircuitcanmaketheoutputvoltagehigherthanthepowersupplyvoltage:first,theinductorLhastheeffectofpumpingupthevoltageafterenergystorage;Second,capacitorCcanmaintaintheoutputvoltage.Intheaboveanalysis,whenVTison,theoutputvoltageremainsunchangedforalongtimeduetotheactionofcapacitorC,butinfact,theCvaluecannotbeinfinite,atthisstagethecapacitorCdischargestotheload,Uwilldecrease,andtheactualoutputvoltagewillbeslightlylowerthanthetheoreticalcalculationresult,butwhenthecapacitorCvalueislargeenough,theerrorgeneratedisverysmallandbasicallynegligible.4.thestep-upchoppercircuit

Thebuck-boostchoppercircuit,alsoknownasthebuck-boostchoppercircuit,isaconversioncircuitthatcanbothboostandbuck.ThecircuittopologyusingIGBTsasswitchingdevicesisshowninFigure5.TheinductorLinthecircuitisverylarge,andthecapacitorCisalsoverylarge,sothattheinductorcurrentandthecapacitorvoltage,thatis,theoutputvoltage,arebasicallyconstant.图5升降压斩波电路5.Buck-boostchoppercircuitTheworkingprincipleofthebuck-boostchoppercircuit:whentheVTisturnedon,thepowersupplysuppliespowertotheinductorLthroughtheVTtostoreenergy;Atthesametime,capacitorCkeepstheoutputvoltagebasicallyconstantandsuppliespowertotheloadL.WhenVTisturnedoff,theenergystoredintheinductorLisreleasedtotheload.Throughtheanalysisofthecircuitdiagram,itcanbeseenthatthepolarityoftheloadvoltageispositiveandnegativeatthebottom,whichisoppositetothepolarityofthepowersupplyvoltage,andtheoutputvoltagepolarityisoppositetotheabove-mentionedstep-downchoppercircuitandstep-upchoppercircuit,sothecircuitisalsocalledreversepolaritychoppercircuit.

Inpureelectricvehicles(sightseeingcars,patrolcars,sweepers,etc.)withaDCdrivemotoroflessthan5kW,thepowerbatterypackdirectlysuppliesDCcurrenttotheDCmotorofthesmallelectricvehicleviaaDC-DCconverter.Inpureelectricvehiclesandfuelcellvehicles,theenergyhybridpowersystemusesastep-upDC-DCconverter;Thepowerhybridpowersystemusesabidirectionalbuck-boostDC-DCconverterorafull-bridgeDC-DCconverter.Whenthevehicleiscoastingorbrakingdownhill,theelectricenergygeneratedbythedrivemotortogeneratepowerisalsochargedtotheenergystoragepowersupplythroughabidirectionalbuck-boostDC-DCconverter.Isolatedstep-downDC-DCconvertersareusedtochargethepowerbatterypackinelectricvehiclestochargeancillaryequipmentandlow-voltagebatteries.AnexampleofaDC-DCconverterisshowninFigure6.Figure6ApplicationexamplesofDC-DCconverters6.ApplicationofDC-DCconverterExpandyourknowledgeOvervoltagegenerationandovervoltageprotectionofpowerelectronicdevicesThepossibleovervoltagesofpowerelectronicdevicesmainlyincludeexternalovervoltagesandinternalovervoltages.Extrinsicovervoltagesmainlycomefromlightningstrikesandoperatingprocessesinthesystem(e.g.,opening,closing,etc.),whileintrinsicovervoltagesmainlycomefromtheswitchingprocessofinternaldevicesinpowerelectronics.

1.Commutationovervoltage

Becausethethyristororthediodeconnectedinreverseparallelwiththefullycontrolleddevicecannotresumeblockingimmediatelyaftertheendofcommutation,thereisalargereversecurrentflowing,andwhentheblockingabilityisrestored,thereversecurrentdecreasessharply,andthelineinductancewillinduceovervoltageatbothendsofthedevice.2.Turnofftheovervoltage

Whenafullycontrolleddeviceisturnedoff,theforwardcurrentdecreasesrapidlyandthelineinductorinducesanovervoltageacrossthedevice.Dependingonthesituation,onlyafewofthesepowerelectronicsmaybeused.Amongthem,themaincircuitandrectifierresistor-capacitanceprotectionaremeasurestosuppresstheinternalovervoltage,andtheirfunctionshavebelongedtothecategoryofbuffercircuits.Amongthemeasurestosuppressexternalovervoltages,RCovervoltagesuppressioncircuitsarethemostcommon.Expandyourknowledge

TheRCovervoltagesuppressioncircuitcanbeconnectedtobothsidesofthepowersupplytransformer(onesideofthepowersupplynetworkiscalledthegr