A new torque and flux control method for switched

IEEETRANSACTIONSONPOWERELECTRONICS,VOL.17,NO.4,JULY2002543ANewTorqueandFluxControlMethodforSwitchedReluctanceMotorDrivesAdrianDavidCheokandYusukeFukudaAbstract—Switchedreluctance(SR)motorshaveanintrinsicsimplicityandlowcostthatmakethemwellsuitedtomanyappli-cations.Howeverthemotor’sdoublysalientstructureandhighlynonuniformtorqueandmagnetizationcharacteristicsleadtotheinabilitytoexcitethemotorusingconventionalacmotorwave-forms,orapplyestablishedacmotorrotatingfieldtheorytothemotor.Furthermore,hightorquerippleisinherentinthemotorunlessatorqueripplereductionstrategyisemployed.Thus,con-trolofthemotorisdifficultandcomplexcomparedtootherma-chines.Previousmethodsofcontrolhavefallenintotwomaincate-gories:thosewhichuseasimplifiedlinearmodelandthosewhichaccountforthemotorsaturation.ThesimplifiedlinearmodelschemeshavetheadvantageofsimplicityandtractabilitybutareinaccurateinmostpracticalSRdrives,whereasthenonlinearschemeshavetheproblemofhighcomplexityandcomputationalexpensivenesswhichmakesreal-timeimplementationdifficult.Toovercometheseproblems,inthispaper,anovelcontrolmethodfortheSRmotorisderivedfromanalysisofthenonuni-formtorquecharacteristicsofthemotor.Thecontrolmethodappliesthephilosophyofdirecttorquecontrol(DTC).UnlikepreviousdirecttorquecontrolschemesfortheSRmotordrive,thenewmethoddoesnotinvolveshortfluxpatterns,achangeofthemotorwindingconfiguration,ortheuseofabipolarcurrentdrive.Thus,theschemecanbeconvenientlyimplementedonanynormaltypeofSRmotordrive.Inaddition,theschemeovercomestheproblemsassociatedwithtorqueripplecontrolintheSRmotorbyregulatingthetorqueoutputofthemotorwithinahysterisisband.Furthermore,theschemeisverysimpleandcanbeimplementedinreal-timewithlowcostmicroprocessorhardware.IndexTerms—Directtorquecontrol,switchedreluctancemotors.I.INTRODUCTIONSWITCHEDreluctance(SR)motorshaveanintrinsicsim-plicityandlowcostthatmakethemwellsuitedtomanyapplications.Furthermore,themotorshaveahighrobustnessduetotheabilitytooperatewiththelossofoneormoremotorphases[1]andarethuswellsuitedtooperateinharshindustrialenvironments.However,themotorhasmanydrawbacksduetothemotor’sdoublysalientstructureaswellashighlynonuniformtorqueoutputandmagnetizationcharacteristics.ThedoublesalientstructureleadstotheinabilitytoexcitethemotorusingconventionalacmotorwaveformsandthustheinabilitytoManuscriptreceivedAugust31,2000;revisedAugust1,2001.Recom-mendedbyAssociateEditorG.K.Dubey.A.D.CheokiswiththeDepartmentofElectricalandComputerEngineering,NationalUniversityofSingapore,Singapore,117576.Y.FukudaiswithMitsubishiElectric,Amagasaki661-8661,Japan.PublisherItemIdentifier10.1109/TPEL.2002.800968.applywellestablishedacmotorrotatingfieldtheorytothemotor.Furthermore,duetothemotor’snonuniformtorqueoutputcharacteristics,ahightorquerippleisinherentinthemotorunlessatorqueripplereductionstrategyisemployed.Additionally,thehighlynonlinearmagnetizationcharacteristicsofthemotorentailthatthecontrolofthemotoriscomplex.Thisisfurthercomplicatedbytheinteractionduetomutualcouplingofdifferentmotorphasesandparametervariationoftheinductancecharacteristics[2],[3].Hence,theproblemofcontrollingtheSRmotorhasbeenanongoingareaofresearch.Thepreviouscontroltechniqueshavefallenintotwomaincategories:thosewhichusedalinearmotormodelandthosewhichusedanonlinearmodelwhichtakesintoaccountthemotorsaturation.Ingeneral,mosttechniquesgen-erateavoltageorcurrentcommandprofileinordertocontrolthemotortorque,speed,positionand/orminimizethetorqueripple.Controlschemesthatusedlinearmotormodelsincludethemethodproposedin[4].ThisschemeusedanadaptivefeedbacklinearisingcontrollerfortheSRmotorwhichassumedalinearmagneticcircuit.Inanotherscheme[5],ananalyticalsolutionforproductionofmotorvoltagestoprovideasmoothtorquewasproposed.Thissolutionwasbasedonthelineartorquecharac-teristicsofthemotor.Otherresearchers[6],[7],haveassumedthattheinductanceprofileofthemotorcanbeexpressedasasimplesinusoidalfunctionthatonlyvarieswithposition.Althoughtheselinearschemeshavetheadvantageofasim-plifiedandreal-timetractablecontrolscheme,disadvantagesarisebecausethehighlysimplifiedmodelsofthemotorwhichareusedareinaccurateinmostpracticalmotordrives.Thisisduetothefactthatthemotorhashighlynonlinearmagnetiza-tioncharacteristicsundernormaloperatingconditionsandthefluxlinkage(andhenceinductance)isanonlinearfunctionsofbothcurrentandposition.ThisisexemplifiedinthemeasureddatashownfromthemotorusedinthisresearchinFig.1.OtherdevelopedschemeshavetakenintoaccountthenonlinearcharacteristicsoftheSRmotor.In[8]afeedbacklinearisingcontrolschemethatprovidescompensationofthemagneticnonlinearitiesofthemotorisdescribed.Themethodhastheadvantageofdecouplingtheeffectofthephasecurrentsinthetorqueproduction.Howeverthemethodrequiresexactknowledgeofthemotorparametersandisthusquiteimpractical.Inaddition,othernonlinearmethodsincludethosewhichgeneratecurrentprofilesforthetorquesharingbetweentwomotorphasesinordertoproduceasmoothtorque[9],[10].Howevertheseschemeslimittheexcitationtotwophasesatatimeandalsorequirecomplexwaveformoptimizationcomputationswhichcannotb