英文原文DSP-BasedHigh-SpeedSensorlessControlforaBrushlessDCMotorUsingaDCLinkVoltageControlDepartmentofElectricalEngineeringKoreaAdvancedInstituteofScienceandTechnologyTaejon,KoreaADSP-basedhighspeedsensorlesscontrolforabrushlessDC(BLDC)motorusingaDClinkvoltagecontrolschemeispresented.ByoperatingtheBLDCmotorinahighspeedrange,thedrivesystemcanhaveasmallsizeandbelightweightatthesameoutputrating.Intheexistingsensorlesscontrolschemes,thePWMtechniqueisgenerallyusedasaspeedcontrol.However,sincethePWMandinvertercommutationcannotbeperformedindependently,asignificantcommutationdelaymayexistinahigh-speedregion.Ontheotherhand,usingtheDClinkvoltagecontrolscheme,theinverterisoperatedwiththesquarewaveof120conductionandthespeedcontrolisachievedbyregulatingtheDClinkinputvoltageoftheinverterthroughthechopper.Byusingthistechnique,sincethevoltagecontrolandcommutationcanbeachievedindependently,acommutatingdelaydoesnotexisteveninahighspeedregion.Also,thephasecurrentcanhaveawaveformsimilartotherectangularwaveandtheterminalvoltageismoree-cienttodealwithinthepositiondetectioncircuits.Thepracticalimplementationissuesconcerningthecommutationdelayinahighspeedsensorlesscontrolarediscussed.ThewholecontrolsystemisimplementedonaBLDCmotorusingDSPTMS320C240andtheeectivenessisveriedthroughthecomparativesimulationsandexperiments.KeywordsbrushlessDCmotor,sensorlesscontrol,DSPcontrol1.IntroductionInmanyindustrialelds,theinstallationofashaftsensormaysignicantlyincreasethedrivecostaswellascomplicatethemotorconfiguration1.Inparticular,foramotorbuiltinacompletelysealedcompressor,ashaftsensorisdifficulttoapplyduetothedegradationofthesensorreliabilityinhightemperatureandtheneedforextraleadwires.Furthermore,thesesensors,particularlyHallsensors,aretemperaturesensitive,limitingtheoperationofthemotortobelowabout75C1.Anabsolutesensorisgenerallyspeedlimitedtoabout6000rpmandaresolverneedsaspecialexternalcircuit.Also,thesensoraccuracymaybeaffectedbytheaccuracyofthemounting.Toovercomethesedrawbacks,sensorlesscontroltechniquesforaBLDCmotorhavebeenproposed1_5.Therearetwocategoriesofpositiondetectionschemes,namely,themethodusingthebackEMFofthemotor2andthemethodbasedonthedetectionoftheconductingintervaloffree-wheelingdiodes3.Intheexistingsensorlesscontrolschemes,thePWMtechniqueisgenerallyusedforaspeedcontrol.However,sincethePWMandinvertercommutationcannotbeperformedindependently,asignicantcommutationdelaymayexistinahighspeedregion.Recently,toimprovethedriveeffciencyandprovidethedesiredcurrentwaveform,asensorlesscontrolschemeusingaquasi-currentsourceinverterhasbeenproposed6.SuchacircuitarrangementisknownasavariableDClinkinverter7.Inthisscheme,theinverterfrequencyiscontrolledtosupplythree-phaserectangularcurrentwithapulsewidthof120andthemotorvoltageforthespeedcontrolisregulatedbyusingastep-downchopperactingasabuckconverter.However,someadvantagesoftheDC-linkvoltagecontrolschemeovertheconventional2-phasePWMschemeinthehighspeedsensorlesscontrolhavenotbeenaddressed.ThisarticlepresentsaDSP-basedhighspeedsensorlesscontrolforaBLDCmotorusingaDClinkvoltagecontrolscheme.BydrivingtheBLDCmotorathighspeed,theoveralldrivesystemcanhaveasmallsizeandalightweightatthesamepowerrating.TocontroltheBLDCmotorathighspeedwithoutashaftsensor,aDSP-basedcontrollerisdevelopedusingTMS320C240.UsingtheDClinkvoltagecontrolscheme,theinverterisoperatedwiththesquarewaveof120conductionintervalandthespeedcontrolisachievedbyregulatingtheDClinkinputvoltageofinverterthroughthechopper.Byusingthistechnique,sincethevoltagecontrolandcommutationcanbeachievedindependently,thecommutatingdelaysuchasintheconventional2-phaseexcitationPWMmethodsdoesnotexisteveninahighspeedregion,whichwillbediscussedinthelatersection.TherotorpositioninformationisdetectedusingthebackEMFfromtheterminalvoltagesofthemotorandtheswitchingsequenceoftheinverter2.ThesensedbackEMFisusedintheintegrationandcomparisoncircuitstoobtainthecommutationsignals.ThedetectedcommutationsignalsareusedtoapplythepropernextsequenceofinverterandobtaintherotationalspeedwithinaDSP.ThecalculatedspeediscontrolledbyadigitalPIcontrolalgorithmandthecontrolleroutputisappliedtothechopper.Thepracticalimplementationissuesconcerningthecommutationdelayofthe2-phaseexcitationPWMschemesathighspeedarediscussedandsomeadvantagesoftheDClinkvoltagecontrolschemeinahighspeedsensorlesscontrolarementioned.ThewholecontrolsystemisimplementedonaBLDCmotorusingDSPTMS320C240andtheeectivenessisveriedthroughthecomparativesimulationsandexperiments.2.SensorlessControlofBLDCMotorABLDCmotorconsideredinthispaperconsistsofpermanentmagnetsmountedontherotorsurfaceandthree-phaseconcentratedstatorwindingsdisplacedby120.Thestatorcurrentsaresuppliedbythe2-phaseexcitationschemewhereonlytwoofthethreephasesareexcitedatanyinstantoftimeandonephaseisconductedduring120period8.Thisexcitationschemedoesnotrequiredeadtimeofthepowerdevices,andfurthermore,theunconductingopen-phasecanbeusefullyutilizedtoobtaintherotorpositioninformation.TherotorpositioninformationaregenerallyobtainedfromtheindirectdetectionmethodusingthemotorbackEMF1_4.In2,therotorpositionhasbeenestimatedfromtheintegrationofthebackEMFwaveform.Thismethodisknowntoprovidetheadvantagessuchasthereducedswitchingnoisesensitivityandautomaticadjustmentoftheswitchinginstantswithoutthephaseshiftof30degrees.Thus,thisdetectionschemeisemployedinthispaper.Thespeedinformationcanbeobtainedfromthederivativeofthedetectedpositionsignals.SincethecommutationsignalsarefedintoaDSPevery60period,ifthecounterclockinDSPisTCandthenumberofcountduring60degreesisa,themechanicalrotorspeedcanbecomputedinrpmasfollows:wherePisthenumberofpoles.3.ProblemsofExistingSensorlessSpeedControlSchemesIntheexistingsensorlesscontrolschemes,the2-phaseexcitationPWMtechniqueisgenerallyemployedforaspeedcontrol.BasedonthemethodexecutingthePWM,PWMschemescanbeclassifiedastheunipolarandbipolarswitchingmethods.Intheunipolarswitchingmethod,thePWMissuperimposedononeofthetwoactiveswitchesinonstate,whiletheotherswitchremainsonstate.Ontheotherhand,inthebipolarswitchingmethod,thetwoactiveswitchesexecutethePWMatthesametime.Sincetheunipolarswitchinghasanadvantageofthereducedswitchingloss,thisschemeisgenerallypreferred4.Also,basedonthepositionthatthePWMissuperimposedon,theunipolarswitchingmethodisclassiedastheon-goingphasePWM,off-goingphasePWM,upperswitchPWM,andlowerswitchPWMschemes.Intheon-goingphasePWMscheme,eachswitchexecutesthePWMduringtherst60degreesofactiveintervalandisheldinonstateduringthesecond60interval,andintheoff-goingphasePWMscheme,viceversa3,4.IntheupperswitchPWMscheme,thePWMisexecutedonlyontheupperoneoftwoactiveswitches,andinthelowerswitchPWMscheme,viceversa.DependingontheusedPWMscheme,thiscontroltechniquemaycauseacommutationdelayoranirregularswitchingfrequencyofthepowerdevicesinahighspeedsensorlesscontrol.Figure1showstherelationbetweenthePWMswitchingperiodandcommutatinginstantinthe2-phaseexcitationPWMscheme.InFigure1,TsandfsdenotethePWMswitchingperiodandfrequency,respectively.Figure1(a)showsacaseoftheidealcommutation.Ascanbeseeninthegure,ifthecommutatinginstantissynchronizedwiththeendofthePWMswitchingperiod,anidealcommutationcanbeobtainedwithoutanydelayintheinvertersequencechange.However,sincethecommutatinginstantdependsontherotorposition,itdoesnotusuallycoincidewiththeendofthePWMperiod.Inthiscase,thecommutationcanbeperformedsynchronizedwiththeendofthepresentPWMperiodtostartanextinvertersequenceasFigure1(b),whichisthenormallyusedmethod.ThisresultsinanundesirablecommutationdelayandthemaximumvalueofthisdelaybecomesthePWMswitchingperiod.Iftheswitchingfrequencyischosenas16kHz,themaximumvalueofthecommutationdelaywillbe62.5sec.Eventhoughthiscommutationdelaycanbeneglectedforamediumspeedrange,ithassignificantinuencesonthephasecurrentresponseanddriveperformanceathighspeedsincethe60-degreeintervalthatthecommutationarisesinisrelativelysmall.Forexample,whena2-polemotorisrotatingat50,000rpm,60-degreeintervalbecomes200sec.ThiscommutatingdelaycanbereducedbyincreasingthePWMswitchingfrequency.Inpractice,however,theswitchingfrequencycannotbeincreasedwithoutlimitbecauseoftheincreasedswitchingloss.Also,theswitchingfrequencyofcommerciallyavailablepowerdevicesislessthan20kHz.Thus,toavoidanundesirablecommutationdelay,thenextinvertersequencehastobeappliedassoonasthecommutationsignalinterruptoccurs.Then,thepresentPWMperiodhastobeterminatedandthenewPWMperiodsynchronizedwiththecommutationinterruptsignalmustbestarted.IntheupperandlowerswitchPWMschemes,thismayyieldanirregularswit