电机学（第七版）（修订版）课件 Chapter-10-Speed-and-Torque-Control

Chapter10SpeedandTorqueControl7/10/2024SpeedandTorqueControl1ControlofDCmotorsSpeedcontrolisoftenperformedwithfield-currentcontrol(shunt,compoundorseparatelyexcited),armature-circuitresistancecontrol(series,shunt,compound,orpermanentmagnet),orarmature-terminalvoltagecontrol(shunt,separatelyexcited,orpermanentmagnet)Armature-circuitresistancecontrolismostoftenusedwithseriesmotors7/10/2024SpeedandTorqueControl2Field-currentcontrol:7/10/2024SpeedandTorqueControl3Field-currentcontrolincreasestheno-loadspeedbyweakeningthefield(reducingif)Armature-terminalvoltagecontroldirectlycontrolstheno-loadspeedbychangingVa7/10/2024SpeedandTorqueControl4Inaseparately-excitedmotor,thearmaturevoltagecontrolcanbeuseduptoratedvoltage,followedbyfieldweakeningtoobtainhigherspeeds7/10/2024SpeedandTorqueControl5wmTBasespeedFieldweakeningArmaturevoltagecontrolPowerlimitTorquelimit7/10/2024SpeedandTorqueControl6Torque(a)andpower(b)limitationsofcombinedarmature-voltageandfield-currentcontrol7/10/2024SpeedandTorqueControl7Armature-voltagecontrolimplementedwithafullH-bridgeinverter.Thedcvoltagemaybearectifieroutputfedbyanacinput.7/10/2024SpeedandTorqueControl8Blockdiagramforaspeed-controlsystemforaseparatelyexcitedorshuntdcmotorBlockdiagramofasimplespeedcontrollerOverallDCmotorspeedcontrolsystemwithdirectcontrolofmotortorque7/10/2024SpeedandTorqueControl9Controlofsynchronousmotors7/10/2024SpeedandTorqueControl10Three-phasevoltage-sourceinverterforvariable-frequencycontrolofanACmotorTomaintaintheair-gapfluxwhenthefrequencyischangedrequiresacorrespondingchangeinvoltage7/10/2024SpeedandTorqueControl11Ifthevoltagefixedatitsratingandthefrequencyisincreased,thefluxwilldrop:Constantvolts-per-hertzmodekeepsratedflux:7/10/2024SpeedandTorqueControl12Powerandtorqueinperunitofratingsplottedversusspeed.Aboveratedspeed,frequencyisincreasedwhilevoltageisatratedvalue.Belowratedspeed,constantvolts-per-hertzcontrolisused.TorquecontrolAppendixCshowsequationsind-qcoordinates:ld=Ldid+Laf

iflq=Lq

iqlf=(3/2)Laf

id+Lffif7/10/2024SpeedandTorqueControl137/10/2024SpeedandTorqueControl14Thisresult(whichisderivedinthetext)showsthatinanon-salientpolemachinetorqueisproducesbytheq-axiscurrentcomponentonlyTheimportanceofthisresultisduetotheabilitytolocatethed-qaxes,forexamplewithapositionsensorWiththeadventofrapidandinexpensivedigitalcomputation,thedqtransformationcanbecomputedinreal-timeforfield-orientedcontrolofACmotors,illustratedinthenextslidefortorqueandspeedcontrol7/10/2024SpeedandTorqueControl157/10/2024SpeedandTorqueControl167/10/2024SpeedandTorqueControl17Field-orientedcontrollerforapermanent-magnetsynchronousmotorControlofinductionmotors7/10/2024SpeedandTorqueControl18Pole-changingmotorsswitchbetweenseveralspeedsbychangingthenumberofpolesFigures(a)and(b)belowillustratechangingfrom4to2polesbyreversingconnectionofcoila’a’Variable-frequencycontrolChangingthefrequency,asintheconstantvolts-per-hertzcontroldiscussedearlierisaneffectivemethodforcontrollingthemotorspeedFiguresbelowshowtorque-speedcurvesforinductionmotorswith(a)neglectingR1and(b)includingR1Thistypeofcontroliswidelyusedforvariablespeedinductionmotordrives7/10/2024SpeedandTorqueControl197/10/2024SpeedandTorqueControl20Thewholetorque-speedcurveisshiftedtoalowerspeedasthefrequencyandvoltagearedecreasedAtlowfrequenciesR1becomessignificantandthepeaktorquedropsSimplyreducingvoltagemakesadrasticreductionintorquewhilereducingthespeedslightlyWound-rotormotorcanuseexternalresistorinserieswiththerotortocontrolthespeed7/10/2024SpeedandTorqueControl217/10/2024SpeedandTorqueControl22Blockdiagramofafield-orientedtorque-controlsystemforaninductionmotor,withanestimateoftheangleofthed-qreferenceframeusedtocomputethedqtoabctransformationSpeedcontrolsystembuiltaroundafield-orientedtorque-controlsystemControlofVRM’s7/10/2024SpeedandTorqueControl23Inverterconfigurations:(a)twoswitchesperphase,(b)splitsupplywithoneswitchperphase,(c)two-phaseinverterwithbifilarphasewindingsandoneswitchperphaseSummarySpeedandtorquecontrolofDCandACmotorswasintroducedRecentyearshaveseengreatstridesincontrolofACmotorsw