外文翻译原文-大功率无刷直流电机的仪器与控制在小型车辆上的应用

InstrumentationandControlofaHighPowerBLDCMotorforSmallVehicleApplicationsAlexanderRowe1,GourabSenGupta1,SergeDemidenko21SchoolofEngineeringandAdvancedTechnology,MasseyUniversity,PalmerstonNorth,NewZealandSchoolofElectronicsandComputerEngineering,RMITInternationalUniversityVietnamARowebto-ltd.co.nz,g.senguptamassey.ac.nz,.vnAbstractBrushlessDC(BLDC)motorsarebecominganincreasinglypopularmotorofchoiceforlowpoweredvehiclessuchasmopeds,powerassistedbicycles,mobilityscooters,andinthisreportedapplication,motorisedmountainboards.Withrapiddevelopmentsintechnology,highenergydensitybatteriessuchasLithium-ionPolymerbatteriesarebecomingmoreaffordableandhighlysuitableforsuchvehiclesduetothesuperiorchargerateandlightweightofthelithiumchemistrybatteries.Thiscombinedwiththehighpower,lightweight,andlowcostBLDCmotorresultsintheBLDCmotorbeingaveryfavourablesolutionoveraninternalcombustionengineforlowpowervehicleswithpowerrequirementsofupto7kW.ABLDCmotorcontrollerwasdevelopedspecificallyforthemotorisedmountainboardapplication.ThemotorcontrollerisasensoredBLDCmotorcontrollerwhichtakesinputsfromHallEffectsensorstodeterminetherotorposition.Manyothersensorsareusedtomonitorthevariablesthatarecriticaltotheoperationofthemotorcontrollersuchasthemotorphasecurrent,batteryvoltage,motortemperature,andtransistortemperature.ThereportedsystemisfurtherenhancedbyseveraladditionalfeaturessuchasoutputforanLCDscreen,regenerativebraking,timingadvance,cruisecontrol,andsoftstartfunctions.Thesetopicsarediscussedbrieflyinthispaper.Keywords-sensoredBLDCmotorcontroller,regenerativebraking,timingadvance,electricskateboard,HallsensorsI.INTRODUCTIONAmotorisedmountainboardallowsuserstotaketheextremesportofmountainboarding,whichisnormallylimitedtodownhilluseonly,toflatanduphillsurfaces.Thisgivestheusersamuchwiderchoiceoflocationswheretheycanusethemountainboard.ABLDCoutrunnermotorhasbeenusedforthisapplication.Anoutrunnermotorwaschosenforitslowspeed(130RPM/v),hightorquecharacteristicswhichreducesthegearingrequirements;a3.8:1gearratioisusedwhichisachievedinadirectchaindrive.ThemotorisaTurnigyC80100-130whichhasapowerratingof6.5kW.Thisamountofpowerissufficienttodrivesmallvehiclestospeedsofapproximately70km/hr;howeverthegearingandbatteryvoltagehasbeenselectedtolimitthemountainboardto50km/hr.Consequently,thetorqueatthewheelsisincreasedandissufficienttoallowthemotorisedmountainboardtoclimbsteephills.AsensorlesscontrollerrequiresthemotortoproduceameasureablebackEMFforthemotorcontrollertobeabletodeterminethepositionoftherotorandthereforecannotprovidesmoothcommutationatstartupandlowspeeds.Incontrast,asensoredBLDCmotorcontrollerusespositionsensorsandthereforeisabletodeterminetherotorpositionatanyspeed.Thisallowsforsmoothcommutationduringstartup.AsensoredBLDCmotorcontrollerwasbuiltforthisreason.II.ELECTRICALSYSTEMOVERVIEWAmixed-signalfieldprogrammablemicrocontroller,theSiliconLaboratoriesC8051F020,hasbeenusedtocontrolthemotordrivercircuitaccordingtoarangeofinputsfromvarioussensors.CustommadesoftwarewasprogrammedinCwhichrunsonthemicrocontroller.Thissoftwaredeterminestheoperationofthemotorcontroller.Fig.1showsthefunctionalblocksofthemotorcontroller.ThemotorcontrollerusesathreephaseH-bridgetodrivethemotor.Thiscircuitwaschosenbecauseitallowsforfourquadrantoperationofthemotor,aswellascoasting.Fig.2showstheschematicdiagramofthethreephaseH-bridge.Figure1Overviewofthemajorcomponentsofthemotorcontroller978-1-4577-1772-7/12/$26.002012IEEEThemotorcontrollerisbuilttomeetthespecificationsofthemotor-themotorcontrollershouldbecapableofsupplying130Aat48Vforburstsof5sandbeabletosupplyatleast40Acontinuously.ThedevicesofchoicefortheswitchesintheH-bridgeareN-channelmetaloxidesemiconductorfieldeffecttransistors(N-MOSFETS).Thesewerechosenfortheirlowcostandtheirabilitytosharecurrentrelativelyevenlywhenparalleledtogether1.Toachievethetargetcurrentcapabilityof130A,twoN-MOSFETSareusedinparallelforeachofthesixswitchesinthethreephaseH-bridge.A.MotorDriverCircuitAgatedriverICisusedbetweenthemicrocontrollerandthegatesoftheMOSFETSforthreereasons:Tostepupthe3.2Vlogicsignalfromthemicrocontrollertoa12VsignalforthelowsidetransistorsinordertosaturatetheMOSFETToprovideachargepumpcircuitfordrivingthegateofthehighsidetransistorsto12VabovethevoltageonthesourcepininordertosaturatetheMOSFETSToprovideshoot-throughprotectionwithprogrammabledeadtimeforthethreephaseH-bridgeGateresistorsbetweentheoutputfromthegatedriverICandMOSFETgateareusedtoslowtheswitchingtimesofthetransistors.Thisistoreducetherateofchangeofcurrent(di/dt)throughthemotorwindings2.Theselfinductanceofthewindingscausesaninducedvoltageacrossthewindingthatisproportionaltotherateofchangeofcurrentwhenthetransistorsareswitchedonandoff.ThisinducedvoltagecancausethetransistorstoexperienceavoltagethatexceedstheVdssrating,causingthemtoblow.Thesegateresistorsarearrangedinawaytoreduceringingissueswiththeparalleledtransistors3.Fig3showstheschematicdiagramforthegateresistorcircuitthatwillreduceringinginahalfbridgecircuit.Thiscanbeextendedifmoretransistorsarerequiredinparallel.Slowingtheswitchingtimeofthetransistorsaloneisnotenoughtoprotectthetransistorsfromblowing;buscapacitorsarealsousedtoabsorbthevoltagespikes2.Lowequivalentseriesresistance(ESR)capacitorsarerequiredbecausethefrequencyofthevoltagespikeisveryhigh(around50MHz).Standardelectrolyticcapacitorsarenotfastenoughtoabsorbtransientvoltagesofsuchfrequencies.TheMotorControllercircuitincorporatesaHallEffectcurrentsensortomeasurethephasecurrentofthemotor.ThisallowstheMotorControllertocutthepowertothemotorifthephasecurrentexceedsthespecifiedlimitinordertoprotectthemotorwindingsfromburningoutandthetransistorsfromblowingduetothecurrentexceedingthemaximumrating.TheHallEffectcurrentsensoroutputisananaloguesignalthatisproportionaltothecurrentflowingthroughawire.Abi-directionalcurrentsensorisusedinthisapplicationtoallowforcurrentmeasurementswhileregenerativebraking.TheMotorControlleralsousesavoltagesensorcircuittotakemeasurementsofthebatteryvoltage.Ifthevoltageislowerthanthespecifiedminimumvoltageofthebattery,themotorcontrollerwillcutthepowertothemotor.ThisisimportantastonotoverdischargetheLithium-ionPolymerbatterypackwhichcanpermanentlyreducethecapacityofthebattery4.Becauseofthewiderangeofoperatingvoltagesthatthemotorcontrollerisabletorunon(from16Vto70V),voltagesensingisdoneusingasimplevoltagedividercircuitwithalowpassRCfilter;alevelshifterisnotused.Temperaturesensorsareinstalledinthemotorandontheheatsinkofthetransistorstoallowthemotorcontrollertocutthepowertothemotorifeitherofthetemperaturesexceedsapre-definedlimit.Theon-boardtemperaturesensorofthemicrocontrollerisalsousedtotakemeasurementsofthemicrocontrollertemperature.Again,themotorcontrollerwillcutthepowerifthemicrocontrollerisoverheating.Thecurrentsensor,voltagesensor,andtemperaturesensorsalloutputanaloguesignals.Becausethesesensorsareincloseproximitytothepowerelectronicsinthemotordrivercircuit,thesmallsignalanalogueoutputsfromthesensorsarehighlysusceptibletonoise.Forthisreason,aRClowpassfilterisusedforeachoftheanaloguesignalstofilteroutthehighfrequencynoise.Eachfilteristunedtofilteranynoisethatisofslightlyhigherfrequencythanthehighestexpectedfrequencyfromthesensor.Figure2.ThreephaseH-bridgecircuitfordrivingaBLDCmotorFigure3.CircuitdiagramforgateresistorstominimizetheeffectofringingintheMOSFETgatesB.RegenerativebrakingThemotorcontrollerincorporatesasimpleregenerativebreakingfunction.Theamountofenergyregeneratedduringnormaluseinaflatoruphillapplicationisverylittle.However,becauseregenerativebrakingistheonlybrakingmethodthatdoesnotsimplyconvertkineticenergyintoheatenergy,whichheatsupthetransistorheatsinkandthemotor,itwasincludedintheproject.RegenerativebrakingisachievedbyboostingthebackEMFofthemotortoahighervoltagethanthebatteryvoltagebyusingaboostconvertercircuit.Fig.4showstheschematicdiagramofabasicboostconvertercircuit5Thiscircuitisimplementedwithoutanyadditionalhardware.ItiscreatedbyusingthelowsidetransistorsofthethreephaseH-bridgeastheswitchingdevice,themotorwindingsastheinductor,andthehighsideflybackdiodesasthediodeintheboostconvertercircuit.Threeofthesecircuitsareinfactused,oneforeachofthethreephases.TheoutputvoltageoftheboostconverteriscontrolledbyvaryingthePWMdutycycleofthelowsidetransistor.Astheoutputvoltageisincreased,thechargingcurrentisincreasedwhichresultsinthebrakingforcebeingincreased.Thereforethebrakingforceiscontrolledbyreadingthepositionofthebrakeleverandadjustingthedutycycleaccordingly.Thechargingcurrenthastobekeptwithinspecifiedlimitstopreventdamagetothebatterypack.FortheLithium-ionPolymerbatterypackusedinthisapplication,themaximumchargingcurrentis20A.Itwascalculatedthat20Aofchargecurrentprovidessufficientbrakepowertoslowdownfrom30km/hrtoacompletestopin3sC.TimingAdvanceTimingadvanceisusedinbothbrushedandbrushlessDCmotors6.InbrushedDCmotorsthisisdonebymechanicallymovingthepositionofthebrushesrelativetothemotorwindings.InBLDCmotors,timingadvanceisdoneelectronicallybycommutatingthemotorsoonerthanitwouldnormallydoso.Ideally,theamountoftimingadvance(expressedasanangleofelectricalrotation)wouldbecontinuouslyvariablefrom0atzerospeedtosomemaximumadvanceangleatthemaximummotorspeed.Thiscanbedonewithamicrocontroller,howeveritrequiresmuchprocessingandwouldrequireadedicatedmicrocontroller7.Thelargeamountofprocessingisrequiredbecausethemicrocontrollermustpredictwhenthenextmotorpositionwilloccurbasedonthespeedofthemotor,andthencalculatethetimedelaybetweenthelastmotorpositiontransitionandthenexttransitionforthedesiredangleofadvance.Withthisinformationthemicrocontrollercantriggerthecommutationatthecalculatedtimeaftertheprevioustransition.D.InternalpositionsensorsInthisapplication,asimpleapproachtotimingadvancehasbeentaken;twosetsofHallEffectsensorshavebeeninstalledinsidethemotor.Onesetispositionedforneutraltiming,theothersetispositioned30(electricalrotation)fromtheneutraltimingset.ThissecondsetofHallEffectsensorsproduceasignalfor30advancedtimingintheforwarddirectionor30retardedtiminginthereversedirection.Thisangleofadvancewasrecommendedby8asanoptimumamountoftimingadvanceforthismotorat5000RPMwhichisnearthetopspeedofthemotorwhenrunningona42Vbattery.Also,becausethemotorhasa12polestator,eachpoleisspaced30apart.ThismeansthatboththeneutraltimingandadvancedtimingsetofHallEffectsensorscanconvenientlybemountedinthegapsbetweenthestatorpoles.Fig.5showswaveformsofthesignalsfromtheneutraland30advancedmotorpositionsensors.Thetopthreewaveformsarefromtheneutraltimingsetandthebottomthreearefromtheadvancedtimingsetofmotorpositionsensors.Thisshowstheadvancedtimingtransitionsoccurring30ofelectricalrotationbeforetheneutraltimingtransitions.Withthisangleoftimingadvance,italsoworksoutthatthesignalfor30advancedtiminginthereversedirectioncanbegeneratedfromthesignalfromthesecondsetofhallsensors.Thisisbecausethesignalfor30retardedtimingisidenticaltothe30advancedsignalwhenphaseshiftedby60(whichisthespacingbetweenmotorpositiontransitions).Thisresultsinthe30retardedsignalbeingexactlyonesequencebehindthe30advancedsignal.Bygeneratingthisthirdsignal,itispossiblefortheMotorboardtouse30advancedtimingintheFigure4.CircuitdiagramshowinghowtheboostconvertercircuitisimplementedusingahalfbridgeFigure5.Waveformsfromtheneutraland30advancedmotorpositionsensorsforwardandreversedirection.Themicrocontrollerisabletoswitchbetweenneutraltimingandadvancedtimingdependingonthespeedofthemotor.Thesoftwaremakesuseofahysteresisbyswitchingtoadvancedtimingat4800RPMandbacktoneutraltimingat4700RPM.III.SOFTWAREDESIGNThemicrocontrollerisprogrammedwithcustommadesoftwaretoallowforadditionalfunctionsthatareuniquetothismotorcontroller.Thesoftwareislargelyinterruptbasedforimprovedcomputationalefficiencyandreliability.Eachtimethemicrocontrollerreadsananalogueinput,eightconsecutivereadingsaretakenandtheaverageofthesereadingsiscalculatedandusedtosetthenewvalueofthevariablethatisbeingread.Thishelpstofurtherreducetheeffectofnoiseontheanaloguesignalsfromthevarioussensors.Distancemeasurementsaredonebycountingthenumberofnewmotorpositions.Forthisparticularmotor,thereare6rotorpositionsinanelectricalrevolution,and7electricalrevolutionsinaphysicalrevolutionofthemotor.Withawheeldiameterof200mmandagearratioof3.8:1,itcanbecalculatedthatafter254newmotorpositions,themountainboardwillhavetravelled1meter.Whenthe“newposition”counterreaches254,thedistancecounterisincrementedby1mandthe“newposition”counterisresettozero.Speedmeasurementisachievedbyusingoneoftheonboardtimerstotimetheintervalbetweentwoconsecutivemotorpositionreadings.Thedistancetravelledforasinglepositionincrementisknownandthereforethespeedcanbecalculated.Athighspeeds,theaverageofeightspeedreadingsisusedforimprovedaccuracy.Fig6illustratesthebasicflowdiagramofthemotorcontrollersoftware.A.SoftStartThepurposeofthesoftstartfunctionistoprotectthemotorandmotordrivercircuitfromexperiencinganovercurrentconditionduringstartup.Thisisrequiredbecausewhenthemotorisatlowspeedorstationary,thereislittleornobackEMFproducedbythemotor.ThebackEMFopposesthevoltageappliedtothemotorterminals,thereforethevoltageexperiencedbythemotoristhedifferencebetweenthesupplyvoltageandthebackEMFvoltage.WithnobackEMF,thevoltageexperiencedbythemotorislarge.Theonlyresistanceinthecircuitisthatoftheon-resistanceofthetransistors(0.008)9,theresistanceofthemotorwindings(0.036),andtheresistanceofthewireswhichisalsoverylow.Thusthecurrentcanreachverylargelevelswhenthemotorisstationaryorrunningatalowspeed.Thesoftstartfunctionlimitsthepowertothemotorasafunctionofspeedatwhichthemotorisrunning.Thisisdonebysettingamaximumallowabledutycycleof5%atzerospeedandincreasingthislimitlinearlyto100%at1900RPM.Thisfunctionisimplementedinthemainloopoftheprogramandthereforedoesnoteffecttheoperationofthecriticalinterruptbasedfunctions.B.CruisecontrolThecruisecontrolfunctionusesPIcontroltomaintainthespeedoftheMotorboardatthespeedsetpoint.Thesetpointistakenasthecurrentspeedatthetimewhenthecruisecontrolisactivatedbyswitchingonthecruisecontrolswitchonthehandheldcontroller.ThePIcontrollervariesthePWMdutycycleinordertomaintainthespeedatthesetpointastheloadchanges,i.e.whentravellingupahill.Thecruisecontrolfunctionisdeactivatedthentheuserappliesthebrakes.Whentheuserstopsusingthebrakes,thenewspeedistakenasthesetpoint.Thevaluesfortheproportionalfactorandintegralfactorwerefoundexperimentally.IV.HANDHELDCONTROLLERTheuserinterfaceforthemotorisedmountainboardisahandheldcontroller.Theshellofaradiocontrolledcartransmitterwasusedasthebaseofthehandheldcontroller.Thisshellwasmodifiedbystrippingoutthecircuitboard,cuttingoffthebatterycase,andmountingaLCDmoduleintoit.Thetriggermechanismwasretainedandisusedastheacceleratorandbrakecontrol(pullbackthetriggertoaccelerate,pushforwardtobrake).Therearetwovariableresistors(rotarypotentiometers)thatarealsoutilised;oneisusedtosetthemaximumdutycycleforthecontroller.ThisallowsthemaximumspeedoftheMotorboardtobelimitedbytheuserwhichisusefulwhensomeoneisusingtheMotorboardforthefirsttime.TheothervariableresistorisusedtocyclethroughthevariousdatathatisFigure6.BasicflowdiagramofthemicrocontrollerprogramdisplayedontheLCDmodule.Therearetwoswitchesthatareusedbythemotorcontroller;oneisusedtoturnthecontrolleronandoff,theotherisusedasthecruisecontrolon/offswitch.ThecompletedMotorboardandthehandheldcontrollerareshowninFig7.TheLCDscreenisonlylargeenoughtodisplaytwolinesof16characters.Inordertodisplaymoredatathanwouldotherwisebepossible,oneofthevariableresistorsinthehandheldcontrollerisusedtoallowtheusertoselectfromarangeofdatascreens.Therearesixdatadisplays:1.Maindatascreen:Displayscurrentspeed,distancetravelled,batteryvoltage,andinstantaneouspoweroutput2.Temperaturescreen:Displaysthetemperatureofthetransistors,motor,microcontroller,andambienttemperature3.Maxvaluescreen:Displaysthemaxspeedreached,maxcurrentdrawn,andmaxpoweroutputduringtherun4.Secondarydatascreen:DisplaysmotorspeedinRPM,andinstantaneouscurrent5.ProgramI/Oscreen:Displaysthemaximumdutycyclelimitsetbytheuser,errorcode,andtripcodefromthemotorcontrollerprogram6.Debugscreen:Displaystheinstantaneousdutycycle,throttlevalue(thevalueusedtosetthePWMdutycycle),andalsowhichtransistorswillbeswitchedonforthecurrentmotorpositionFigure7.MotorboardandthehandheldcontrollerV.EXPERIMENTALRESULTSExperimentalresultsshowtheon-boarddistancemeasurementtobeaccurateto0.5%whenmeasuredagainstatapemeasure.Theresolutionofthismeasurementallowsthesoftwaretomeasuredistancesassmallas4mm.However,thereisuncertaintyintroducedinthemeasurementbythediameterofthewheel.Thewheelsareinflatableandthereforethediameterchangesslightlydependingontheairpressureandthemassoftherider.Alaparounda400mathleticstrackhasshownthedistancemeasurementtobewithin1mofaccuracy.Anexperimentwasalsoconductedtotesttheaccuracyoftheon-boardspeedmeasurement.TheMotorboardwasbroughtuptoanarbitraryspeedof17km/hrontheLCDscreenandheldatthatspeed.Itwasthenfilmedpastinga5mtapemeasure.Thevideorecordingwasthenreviewedtodeterminethetimetakentotravelthe5mdistance.Itwascalculatedthattheactualspeedforthisrunwas17.42km/hr.Thisexperimentwasrepeatedataspeedof25km/hraccordingtotheon-boardinstrumentation.Thecalculatedactualspeedforthisrunwas25.68km/hr.Theseresultsestablishthatthespeedmeasurementreadsslightlylow;howeveritisinaccuratebylessthan1km/hrforspeedsoflessthan25km/hr.VI.CONCLUSIONANDFUTUREWORKAswithanyprototype,thereismuchroomforimprovement.Oneareaforimprovementisthecommutationofthemotorbasedonthepositionsensorreadings.Currentlythisisdonebyreadingthemotorpositionatafrequencyof30kHztocheckforanewmotorposition.Thecommutationfunctioncanbedonemoreefficientlyusinganinterruptbasedtrigger.TheSiliconLaboratoriesC8051F020hasfourexternalinterruptpinsthatcanbeconfiguredaseitherrisingedgesensitiveorfallingedgesensitive,notboth.Thereforesixexternalinterruptpinswouldberequiredinordertotriggeraninterruptforanymotorpositiontransition.Adifferentmicrocontrollershouldbeusedthatwillallowforthemotorcommutationtobedoneentirelybasedoninterrupts.Thiswillimprovetheaccuracyofthetimingofthecommutationsandsignificantlyreducethecomputa