电力电子 变频传动Word文档格式.docx

电力电子 变频传动Word文档格式.docx

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李志强俞卫金雪峰薛梅

6.1Introduction

6.2PMACMachineControlFundamentals

6.3TrapezoidalPMACMachineControl

6.4SinusoidalPMACMachineControl

6.5AdvancedControlTechniques

6.6PmacDriveApplicationIssues

6.7Conclusion

References

6.1.INTRODUCTION

PermanentmagnetAC（PMAC）machinesprovideauniquesetofadvantagesandopportunitiestodesignersofmodernmotioncontrolsystems.PMACmachinescanbedesignedinmanydifferentgeometriesasdiscussedinChapter2,andafewcommonexamplesareillustratedinFigure6-1.TheuseofpermanentmagnetstogeneratesubstantialairgapmagneticfluxwithoutexternalexcitationmakesitpossibletodesignPMACmachineswithunsurpassedefficiencycharacteristics.Suchefficiencyadvantagesarebecomingincreasinglyvaluableinmanypartsoftheworldwheremarketforcesandgovernmentalmandatesarefocusingincreasedattentiononreducedenergyconsumptioninmanytypesofelectricalequipment.Forexample,minimumenergyefficiencyrequirementsaregraduallybeingimposedbytheU.S.governmentduringthe1990sonmajorclassesofresidentialappliancesaswellasheating,ventilating,andairconditioning（HVAC）equipment[1].

Alternatively,thelowlossesmadepossiblebytheappropriateapplicationofpermanentmagnetscanbeusedtoachievemachinedesignswithimpressivelyhighvaluesofpowerdensityandtorque-to-inertia（Te/J）ratios[2].ThesecharacteristicsmakePMACmachineshighlyattractiveformanyactuatorandservoapplicationsthatdemandthefastestpossibledynamicresponse.

Ontheotherhand,PMACmachinespresentspecialchallengestotheelectricalequipmentdesignersincetheyaresynchronousmachinesthat,intheabsenceofauxiliaryrotorwindings,absolutelyrequireaccompanyingpowerelectronicsforoperation.ThedriveelectronicsisnecessarytoperfectlysynchronizetheACexcitationfrequencywiththerotationalspeedasaprerequisiteforgeneratingusefulsteady-statetorque,incontrasttoaninductionmotorwhichtypicallyoperatesfromafixedfrequencyACsource（50or60Hz）.Asaresult,PMACmachinesareparticularlywellsuitedtomotioncontrolapplicationsthatcanjustifythecostofthepowerelectronicstotakeadvantageoftheuniquelyattractiveefficiencyanddynamicresponsecharacteristicsprovidedbythistypeofmachine.

Theobjectiveofthischapteristoreviewtheprincipalmotioncontroltechniquesthathavebeendevelopedsincethe1970sforPMACmachinedrives.TwomajorclassesofPMACmachines—trapezoidalandsinusoidal—wereintroducedinChapter2thathavesomenotabledifferencesintheirrespectivecontrolrequirementsandperformancecharacteristics.AmajorportionofthischapterwillbedevotedtoadiscussionofthecommonalitiesanddifferencesassociatedwiththecontrolofthesetwoimportantfamiliesofPMACmachines.ThespecialcontrolrequirementsofPMACmachinestoachieveextendedspeedoperatingrangesusingflux-weakeningtechniqueswillalsobeaddressed.

TheparticularrequirementsofPMACmachinesforsynchronizationoftheexcitationwaveformswithrotationalspeedhavegivenrisetoaconsiderablevarietyofcontroltechniquesforeliminatingtheshaft-mountedpositionsensorthatwillbereviewedlaterinthischapter.ThisdiscussionofadvanceddrivecontroltechniqueswillbefollowedbyacomparisonofthestrengthsandweaknessesofPMACmachinedrivescomparedtoothermajorcompetingmachinedrivetechnologies.ThechapterwillconcludewithsummarydescriptionsofseveralPMACmachinedrivesystemsthathavebeenselectedtoillustratethebreadthoffieldedapplications,leadingtoaclosingdiscussionofexpectedfuturetrends.

6.1.1.Background

PMACmachinedrivesrepresenttheconvergenceofatleasttwodistinctthreadsofpermanentmagnetmachinedevelopment.Oneofthesethreadsistheearlydevelopmentofline-startPMACmotorswithembeddedrotorsquirrelcagewindingsdesignedforoperationdirectlyfromutility-suppliedACpower.WorkonthisspecialclassofhybridPMACinductionmachinedatesbacktothe1950s[3,4]usingAlnicomagnets.Thesemachineswerewidelyappliedinsomeimportantindustrialapplicationssuchastextilemanufacturinglinesthatrequirelargenumbersofmachinesoperatingatidenticalspeeds[5].

Laterduringthe1970s,considerableresearchattentionwasfocusedonimproveddesignsforline-startPMACmachinesasameansofachievingsignificantenergysavingsinindustrialapplications.Integralhorsepowerversionsoftheseline-startPMACmotorshavebeendevelopedwithimpressiveefficiencycharacteristicsusingbothferriteandrare-earthmagnets[6],buttheirresultingmanufacturingcostpremiumsoverconventionalinductionmachinespreventedwidemarketacceptance.Nevertheless,significanttechnicalprogresshasbeendemonstratedinthedevelopmentofthesehigh-powerPMACmachines,andworkinthisareacontinuestoday[7].

Representingthesecondthreadofdevelopment,permanentmagnetDC（PMDC）servomotorsbegantodisplaceconventionalwound-fieldDCmotorsinhigh-performancemachinetoolservoapplicationsinthe1960swhensolid-stateDCchoppercircuitsreachedmarketmaturity[8].Theavailabilityofhigh-strengthrareearthpermanentmagnetsmadeitpossibletodevelopcompactfast-responsePMDCservomotors[9]withoutthesteady-statelossesandadditionalcircuitcomplicationsassociatedwithtraditionalwound-fieldDCmachines.

Finally,inthe1970s,thesetwodevelopmentpathsconvergedasPMACmachines（withoutrotorcages）werecombinedwithadjustablefrequencyinverterstoachievehigh-performancemotioncontrol[10].ThisapproachhadthedesirableeffectofeliminatingthedualdisadvantagesofhighrotorinertiaandbrushwearassociatedwithPMDCmotorcommutators.Theclassof"

brushlessDCmotors"

usingtrapezoidalPMACmotorswasdevelopedfirst[11]inordertotakeadvantageofthecontrolsimplificationsthatareachievablewiththisconfiguration,asdiscussedinmoredetailinSection6.3.Thishasbeenfollowedbytheevolutionofhigh-performancesinusoidalPMACmachinedrivesduringthelate1970sand1980swhichhavebeenmadepossiblebytherapidadvancesindigitalreal-timecontrolhardwareandvectorcontroltechnologyfirstappliedtoinductionmotors[12].

6.1.2.MotionControlPerformanceRequirements

AlthoughseveralofthebasicissuesassociatedwithmachinedrivespecificationswereintroducedinChapter2,afewkeypointswillbebrieflyreviewedhereinordertosetthestageforthefollowingdiscussionofPMACmachinecontroltechniques.Torque-speedenveloperequirementsforPMACmachinedrivestypicallyfallintooneoftwoclassesillustratedinFigure6-2."

Constanttorque"

applicationsarecharacterizedbythesquaretorque-speedenvelopeshowninFigure6-2awhichrequiresthatmaximumtorque

beavailableatallspeedsuptothemaximumrotorspeed

.Actuatorsandservosystemsaretypicalexamplesofconstanttorqueapplicationswhichrelyonmaximumtorqueavailabilityatallspeedstoensuremaximumdynamicresponse.PMACmachinesarenaturallywellsuitedforconstanttorqueapplicationsbecauseoftheconstantlevelofmagneticfluxdeliveredbytherotorpermanentmagnetstothemachine'

sairgap.

Incontrast,"

constanthorsepower"

applicationsarecharacterizedbyatorque-speedenvelopewhichfollowsahyperbolicconstantpowertrajectory（Te-ωr=P0=constant）overawidespeedrangeabovebasespeedωbasillustratedinFigure6-2b.Oneofthemostfamiliarexamplesofaconstanthorsepowerapplicationiselectricvehicletractionthatrequireshightorqueforlow-speedaccelerationandreducedtorqueforhigh-speedcruising.ConstanthorsepoweroperationposesspecialchallengesforPMACmachinessincethereisnofieldwindingwhichcanbedirectlyweakenedasinaconventionalseparatelyexcitedDCmotor.However,"

flux-weakening"

controltechniquesareavailableforPMACmachinesthatcanachievethesameeffect,asdescribedlaterinthischapter.

Althoughtheprecedingdiscussionhasbeenframedintermsofsingle-quadrantmotoringoperationwithpositivetorqueandpositivespeed,manyapplicationsrequirethatthePMACmachinedevelopbrakingtorqueforcontrolleddecelerationandthatthemachinebeabletorotateinbothdirections.Suchrequirementsgiverisetotwo-andfour-quadranttorque-speedoperatingenvelopesasdiscussedpreviouslyinChapter2.ThePMACmachineiswellsuitedforsuchapplicationssinceitcanoperateequallywellasamotororgenerator,anddirectionofrotationhasnoimpactonthemachine'

sperformancecharacteristics.

PMACmachinedriveapplicationscanbefurthercharacterizedfromacontrolstandpointbythenatureoftheprimarycontrolvariable.Thethreeprincipaltypesofdrivecontrolconfigurationsaretorquecontrol,speedcontrol,andpositioncontrol.Torquecontrolrepresentsthemostbasiccontrolrequirements,typifiedbytheacceleratorandbrakepedalsofanelectricvehicledrive.Manyotherindustrialandcommercialapplicationssuchaspumpsandprocesslinesrequirespeedcontrol,representinganintermediatelevelofcontrolperformancerequirements.Finally,positioncontrolsystemsgiverisetosomeofthemostdemandingmotioncontrolrequirementsforhigh-performanceapplicationssuchasmachinetoolservos.Motioncontrolperformancerequirementsarealsoreflectedindynamicresponsespecifications.Forexample,dynamicresponserequirementsforaPMACspeed-orposition-controlledservosystemaretypicallyexpressedintermsofbandwidthspecificationswhichdefinetheabilityofthedrive'

soutputshafttofaithfullytracksinuso