電電機(jī)分類的介紹英文課件

SeanDeHartSmritiChopraHannesDaepp2Overview

DCMotors(BrushedandBrushless)BriefIntroductiontoACMotorsStepperMotorsLinearMotorsSeanDeHart3ElectricMotorBasicPrinciplesInteractionbetweenmagneticfieldandcurrentcarryingwireproducesaforceOppositeofageneratorSeanDeHart4Conventional(Brushed)DCMotorsPermanentmagnetsforouterstatorRotatingcoilsforinnerrotor

CommutationperformedwithmetalcontactbrushesandcontactsdesignedtoreversethepolarityoftherotorasitreacheshorizontalSeanDeHart52polebrushedDCmotorcommutationSeanDeHart6Conventional(Brushed)DCMotorsCommonApplications:Small/cheapdevicessuchastoys,electrictoothbrushes,smalldrillsLab3Pros:Cheap,simpleEasytocontrol-speedisgovernedbythevoltageandtorquebythecurrentthroughthearmatureCons:Mechanicalbrushes-electricalnoise,arcing,sparking,friction,wear,inefficient,shortingSeanDeHart7DCMotorconsiderationsBackEMF-everymotorisalsoageneratorMorecurrent=moretorque;morevoltage=morespeedLoad,torque,speedcharacteristicsShunt-wound,series-wound(akauniversalmotor),compoundDCmotorsSeanDeHart8BrushlessDCMotorsEssentialdifference-commutationisperformedelectronicallywithcontrollerratherthanmechanicallywithbrushesSeanDeHart9BrushlessDCMotorCommutationCommutationisperformedelectronicallyusingacontroller(e.g.HCS12orlogiccircuit)Similaritywithsteppermotor,butwithless#polesNeedsrotorpositionalclosedloopfeedback:halleffectsensors,backEMF,phototransistorsSeanDeHart10Delta

WyeBLDC(3-Pole)MotorConnectionsHas3leadsinsteadof2likebrushedDCDelta(greaterspeed)andWye(greatertorque)statorwindings

SeanDeHart11BrushlessDCMotorsApplicationsCPUcoolingfansCD/DVDPlayersElectricautomobilesPros(comparedtobrushedDC)HigherefficiencyLongerlifespan,lowmaintenanceClean,fast,nosparking/issueswithbrushedcontactsConsHighercostMorecomplexcircuitryandrequiresacontrollerSeanDeHartACMotorsTwomaintypesofACmotor,SynchronousandInduction.Synchronousmotorssupplypowertoboththerotorandthestator,whereinductionmotorsonlysupplypowertothestatorcoils,andrelyoninductiontogeneratetorque.12SeanDeHart13ACInductionMotors(3Phase)Usepoly-phase(usually3)ACcurrenttocreatearotatingmagneticfieldonthestatorThisinducesamagneticfieldontherotor,whichtriestofollowstator-slippingrequiredtoproducetorqueWorkhorsesoftheindustry-highpoweredapplicationsSeanDeHartACinductionMotorsInductionmotorsonlysupplycurrenttothestator,andrelyonasecondinducedcurrentintherotorcoils.Thisrequiresarelativespeedbetweentherotatingmagneticfieldandtherotor.Iftherotorsomehowmatchesorexceedsthemagneticfieldspeed,thereisconditioncalledslip.Slipisrequiredtoproducetorque,ifthereisnoslip,thereisnodifferencebetweentheinducedpoleandthepoweredpole,andthereforenotorqueontheshaft.14SeanDeHartSynchronousACMotorsCurrentisappliedtoboththeRotorandtheStator.Thisallowsforprecisecontrol(steppermotors),butrequiresmechanicalbrushesorslipringstosupplyDCcurrenttotherotor.Thereisnoslipsincetherotordoesnotrelyoninductiontoproducetorque.

15SeanDeHartStepperMotorAsteppermotorisanelectromechanicaldevicewhichconvertselectricalpulsesintodiscretemechanicalmovements.Theshaftorspindleofasteppermotorrotatesindiscretestepincrementswhenelectricalcommandpulsesareappliedtoitinthepropersequence.SmritiChopraMainfeatures

Thesequenceoftheappliedpulsesisdirectlyrelatedtothedirectionofmotorshaftsrotation.Thespeedofthemotorshaftsrotationisdirectlyrelatedtothefrequencyoftheinputpulses.Thelengthofrotationisdirectlyrelatedtothenumberofinputpulsesapplied.SmritiChopraStepperMotorCharacteristics

Openloop

Themotorsresponsetodigitalinputpulsesprovidesopen-loopcontrol,makingthemotorsimplerandlesscostlytocontrol.

Brushless

Veryreliablesincetherearenocontactbrushesinthemotor.Thereforethelifeofthemotorissimplydependantonthelifeofthebearing.

Incrementalsteps/changes

Therotationangleofthemotorisproportionaltotheinputpulse.

Speedincreases->torquedecreasesSmritiChopraTorquevs.SpeedTorquevariesinverselywithspeed.Currentisproportionaltotorque.Torque→∞meansCurrent→∞,whichleadstomotordamage.Torquethusneedstobelimitedtoratedvalueofmotor.SmritiChopraDisadvantagesofsteppermotorsTherearetwomaindisadvantagesofsteppermotors:Resonancecanoccurifnotproperlycontrolled.Thiscanbeseenasasuddenlossordropintorqueatcertainspeedswhichcanresultinmissedstepsorlossofsynchronism.Itoccurswhentheinputsteppulseratecoincideswiththenaturaloscillationfrequencyoftherotor.Resonancecanbeminimisedbyusinghalfsteppingormicrostepping.

Noteasytooperateatextremelyhighspeeds.20WorkingprincipleSteppermotorsconsistofapermanentmagnetrotatingshaft,calledtherotor,andelectromagnetsonthestationaryportionthatsurroundsthemotor,calledthestator.Whenaphasewindingofasteppermotorisenergizedwithcurrent,amagneticfluxisdevelopedinthestator.Thedirectionofthisfluxisdeterminedbythe“RightHandRule”.SmritiChopraAtposition1,therotorisbeginningattheupperelectromagnet,whichiscurrentlyactive(hasvoltageappliedtoit).Tomovetherotorclockwise(CW),theupperelectromagnetisdeactivatedandtherightelectromagnetisactivated,causingtherotortomove90degreesCW,aligningitselfwiththeactivemagnet.Thisprocessisrepeatedinthesamemanneratthesouthandwestelectromagnetsuntilweonceagainreachthestartingposition.SmritiChopraUnderstandingresolutionResolutionisthenumberofdegreesrotatedperstep.Stepangle=360/(NPh*Ph)=360/NNPh=Numberofequivalentpolesperphase=numberofrotorpoles.Ph=Numberofphases.N=Totalnumberofpolesforallphasestogether.Example:forathreewindingmotorwitharotorhaving4teeth,theresolutionis30degrees.SmritiChopraTwophasesteppermotorsTherearetwobasicwindingarrangementsfortheelectromagneticcoilsinatwophasesteppermotor:bipolarandunipolar.unipolarbipolarSmritiChopraAunipolarsteppermotorhastwowindingsperphase,oneforeachdirectionofmagneticfield.Inthisarrangementamagneticpolecanbereversedwithoutswitchingthedirectionofcurrent.Bipolarmotorshaveasinglewindingperphase.Thecurrentinawindingneedstobereversedinordertoreverseamagneticpole. Bipolarmotorshavehighertorquebutneedmorecomplexdrivercircuits.MaindifferenceSmritiChopraSteppingmodesWaveDrive(1phaseon)A1–B2–A2–B1(25%ofunipolarwindings,50%ofbipolar)FullStepDrive(2phaseson)A1B2–B2A2–A2B1–B1A1(50%ofunipolarwindings,fullbipolarwindingsutilization)HalfStepDrive(1&2phaseson)A1B2–B2–B2A2–A2(increasesresolution)Microstepping(Continuouslyvaryingmotorcurrents)Amicrostepdrivermaysplitafullstepintoasmanyas256microsteps.SmritiChopraTypesofStepperMotorsTherearethreemaintypesofsteppermotors:VariableReluctancesteppermotorPermanentMagnetsteppermotorHybridSynchronoussteppermotorSmritiChopraThistypeofmotorconsistsofasoftironmulti-toothedrotorandawoundstator.WhenthestatorwindingsareenergizedwithDCCurrent,thepolesbecomemagnetized.Rotationoccurswhentherotorteethareattractedtotheenergizedstatorpoles.VariableReluctancemotorSmritiChopraPermanentMagnetmotorTherotornolongerhasteethaswiththeVRmotor.Insteadtherotorismagnetizedwithalternatingnorthandsouthpolessituatedinastraightlineparalleltotherotorshaft.ThesemagnetizedrotorpolesprovideanincreasedmagneticfluxintensityandbecauseofthisthePMmotorexhibitsimprovedtorquecharacteristicswhencomparedwiththeVRtype.SmritiChopraHybridSynchronousmotorTherotorismulti-toothedliketheVRmotorandcontainsanaxiallymagnetizedconcentricmagnetarounditsshaft.Theteethontherotorprovideanevenbetterpathwhichhelpsguidethemagneticfluxtopreferredlocationsintheairgap.SmritiChopraApplications

Steppermotorscanbeagoodchoicewhenevercontrolledmovementisrequired.Theycanbeusedtoadvantageinapplicationswhereyouneedtocontrolrotationangle,speed,positionandsynchronism.

Theseincludeprintersplottersmedicalequipmentfaxmachinesautomotiveandscientificequipmentetc.SmritiChopraLinearMotors

HannesDaeppHannesDaeppBasicsofLinearMotors[1],[4]IAnalogoustoUnrolledDCMotorForce(F)isgeneratedwhenthecurrent(I)(alongvectorL)andthefluxdensity(B)interactF=LIxBHannesDaeppLinearMotorsinAction/video/Braas_Trilogy_T3E_Video.MPGHannesDaeppAnalysisofLinearMotors[1],[5]AnalysisissimilartothatofrotarymachinesLineardimensionanddisplacementsreplaceangularonesForcesreplacetorquesCommutationcycleisdistancebetweentwoconsecutivepolepairsinsteadof360degreesHannesDaeppBenefitsofLinearMotors[2]HighMaximumSpeedLimitedprimarilybybusvoltage,controlelectronicsHighPrecisionAccuracy,resolution,repeatabilitylimitedbyfeedbackdevice,budgetZerobacklash:Nomechanicaltransmissioncomponents.FastResponseResponseratecanbeover100timesthatofamechanicaltransmissionfasteraccelerations,settlingtime(morethroughput)StiffnessNomechanicallinkage,stiffnessdependsmostlyongain¤tDurableModernlinearmotorshavefew/nocontactingpartsnowearHannesDaeppDownsidesofLinearMotors[2]CostLowproductionvolume(relativetodemand)HighpriceofmagnetsLinearencoders(feedback)aremuchmoreexpensivethanrotaryencoders,costincreaseswithlengthHigherBandwidthDrivesandControlsLowerforceperpackagesizeHeatingissuesForcerisusuallyattachedtoloadI2RlossesaredirectlycoupledtoloadNo(minimal)FrictionNoautomaticbrakeHannesDaeppComponentsofLinearMotors[2],[3]Forcer(MotorCoil)Windings(coils)providecurrent(I)WindingsareencapsulatedwithincorematerialMountingPlateontopUsuallycontainssensors(halleffect

andthermal)MagnetRailIronPlate/BasePlateRareEarthMagnetsofalternatingpolarityprovideflux(B)SingleordoublerailF=

lIxBHannesDaeppTypesofLinearMotors[1],[2],[3]IronCoreCoilswoundaroundteethoflaminationsonforcer

IronlessCoreDualbackironseparatedbyspacerCoilsheldtogetherwithepoxy

SlotlessCoilandbackironheldtogetherwithepoxyHannesDaeppLinearMotorTypes:IronCore[1],[2]DistinguishingFeatureCopperwindingsaroundforcerlaminationsoverasinglemagnetrailAdvantages:HighestforceavailableperunitvolumeEfficientCoolingLowercostDisadvantages:Highattractiveforcebetweenforcer&magnettrackCogging:ironforceraffectsthrust

forceasitpassesovereach

magnet(akavelocityripple)HannesDaeppDistinguishingFeatureForcerconstructedofwoundcoilsheldtogetherwithepoxyandrunningbetweentworails(NorthandSouth)Alsoknownas“Aircore”or“U-channel”motorsAdvantages:NoattractiveforcesinforcerNoCoggingLowweightforcer-Noironmeanshigheraccel/decelratesTopViewForcerMountingPlateRareEarthMagnetsHorseshoeShapedbackironWinding,heldbyepoxyHallEffectandThermalSensorsincoilFrontViewLinearMotorTypes:Ironless[1],[2]Disadvantages:LowforceperpackagesizeLowerStiffness;limitedmaxloadwithoutimprovedstructurePoorheatdissipationHighercost(2xMagnets!)HannesDaeppDistinguishingFeatureMixofironlessandironcore:coilswithbackironcontainedwithinaluminumhousingoverasinglemagnetrailAdvantagesoverironless:Lowercost(1xmagnets)BetterheatdissipationStructurallystrongerforcerMoreforceperpackagesizeAdvantagesoverironcore:LighterweightandlowerinertiaforcerLowerattractiveforcesLesscoggingSideViewFrontViewBackironMountingplateCoilassemblyThermalsensorRareEarthMagnetsIronplateLinearMotorTypes:Slotless[1],[2]HannesDaeppDisadvantagesSomeattractiveforceandcoggingLessefficientthanironcoreandironless-moreheattodothesamejobSideViewFrontViewBackironMountingplateCoilassemblyThermalsensorRareEarthMagnetsIronplateLinearMotorTypes:Slotless[2],[3]HannesDaeppLinearBrushlessDCMotorTypeFeatureIronCoreIronlessSlotlessAttractionForceMostNoneModerateCostMediumHighLowestForceCoggingHighestNoneMediumPowerDensityHighestMediumMediumForcerWeightHeaviestLightestModerateLinearMotorTypeComparison[2]HannesDaeppComponentsofa“Complete”LinearMotorSystem[3]Motorc