第10章 直流无刷电机-4

IntroductionBLDCmotorsareoneofthemotortypesrapidlygainingpopularity.BLDCmotorsareusedinindustriessuchasAutomotive,Aerospace,Consumer,Medical,IndustrialAutomationEquipmentandInstrumentation.Asthenameimplies,BLDCmotorsdonotusebrushesforcommutation;instead,theyareelectronicallycommutated.BrushlessDCelectricmotor(BLDCmotors)alsoknownaselectronicallycommutatedmotorsaresynchronousmotorsthatarepoweredbyaDCelectricsourceviaaninverter,whichproducesanACelectricsignaltodrivethemotor(AC,alternatingcurrent,doesnotimplyasinusoidalwaveformbutratherabi-directionalcurrentwithnorestrictiononwaveform);additionalsensorsandelectronicscontroltheinverteroutputamplitudeandwaveformandfrequency(i.e.rotorspeed).ABrushlessDCmotorconsistsofthreeparts,amotor,therotorpositionsensorsandelectronicswitchingcircuit.principleblockdiagramofabrushlessDCmotorisshowninfig.10-1.DCpowersupplySwitchingcircuitMotorPositionSensorOutputFig.10-1principleblockdiagramofbrushlessDCmotorsScooterFigure10-1BLDCmotorsBLDCmotorshavemanyadvantagesoverbrushedDCmotorsandinductionmotors.Afewoftheseare:•Betterspeedversustorquecharacteristics•Highdynamicresponse•Highefficiency•Longoperatinglife•Noiselessoperation•HigherspeedrangesInaddition,theratiooftorquedeliveredtothesizeofthemotorishigher,makingitusefulinapplicationswherespaceandweightarecriticalfactors.Wewilldiscussindetailtheconstruction,workingprinciple,characteristicsandtypicalapplicationsofBLDCmotors.10.2FUNDAMENTALCONSTRUCTIONANDOPERATINGPRINCIPLE

BLDCmotorsareatypeofsynchronousmotor.Thismeansthemagneticfieldgeneratedbythestatorandthemagneticfieldgeneratedbytherotorrotatesatthesamefrequency.BLDCmotorsdonotexperiencethe“slip”thatisnormallyseenininductionmotors.BLDCmotorscomeinsingle-phase,2-phaseand3-phaseconfigurations.Correspondingtoitstype,thestatorhasthesamenumberofwindings.Outofthese,3-phasemotorsarethemostpopularandwidelyused.10.2.1CONSTRUCTIONFigure10-2Construction1)StatorThestatorofaBLDCmotorconsistsofsteellaminationswithwindingsplacedintheslotsthatareaxiallycutalongtheinnerperiphery.Traditionally,thestatorresemblesthatofaninductionmotor;however,thewindingsaredistributedinadifferentmanner.MostBLDCmotorshavethreestatorwindingsconnectedinstarfashion.Eachofthesewindingsareconstructedwithnumerouscoilsinterconnectedtoformawinding.OneormorecoilsareplacedintheslotsandtheyareFigure10-3Statorinterconnectedtomakeawinding.Eachofthesewindingsaredistributedoverthestatorperipherytoformanevennumbersofpoles.Figure10-3Thearmaturewindingconnectionsareshowninfigure10-4.(a)3-phase,star,3-state;(b)4-phase,star,4-state(c)3-phase,star,6-state(d)2-phase,orthogonal,4-state

Figure10-4Armaturewindingconnection (e)3-phase,delta,6-state;(f)4-phase,closed,4-state2)RotorThefollowingfigure10-6showscrosssectionsofdifferentarrangementsofmagnetsinarotor.Figure10-6UnlikeabrushedDCmotor,thecommutationofaBLDCmotoriscontrolledelectronically.TorotatetheBLDCmotor,thestatorwindingsshouldbeenergizedinasequence.Itisimportanttoknowtherotorpositioninordertounderstandwhichwindingwillbeenergizedfollowingtheenergizingsequence.RotorpositionissensedusingHalleffectsensorsembeddedintothestator.3)HallSensorsMostBLDCmotorshavethreeHallsensorsembeddedintothestatoronthenon-drivingendofthemotor.WhenevertherotormagneticpolespassneartheHallsensors,theygiveahighorlowsignal,indicatingtheNorSpoleispassingnearthesensors.BasedonthecombinationofthesethreeHallsensorsignals,theexactsequenceofcommutationcanbedetermined.CDROMHallSensorPositions(4)Electro-magneticpositionsensor10.2.2TheoryofOperation1)Theoperationprincipleof3-phase,star,3-statesystemisexplainedwithfigure8.Figure10-8Operationprincipleelectricalangle02π/34π/32πconductionanglesofstatewindingABCconductingtransistorV1V2V3Table10-1Conductionsequencetableof3-phase,star,3-statesystemFigure10-9PhasevoltageswaveformsofBLDCFig.10-10Torquewaveform2)3-phase,star,bridgeconnectionFig.10-123-phase,star,bridgeconnectionV1V6(A+C-)→V6V2(B+C-)→V2V4(B+A-)→V4V3(C+A-)→V3V5(C+B-)→V5V1(A+B-)→V1V6(A+C-)Table10-2Conductionsequencetableof3-phase,star,6-statesystemElectricalangle0π/32π/3π

4π/35π/32πConductionsequenceABCBCABV1TurnonV2TurnonV3TurnonV4TurnonV5TurnonTurnonV6TurnonFigure10-13Torquevectordiagram3)3-phase,closed,bridgeconnection.Figure10-143-phase,closed,bridgeconnection

V1V6[A+//(C-→B-)]→V6V2[B-//(C+→A+)]→V2V4[C+//(B-→A-)]→V4V3[A-//(B+→C+)]→V3V5[B+//(A-→C-)]→V5V1[C-//(A+→B+)]→V1V6[A+//(C-→B-)]Table10-3Conductionsequencetableofclosed,star,6-statesystemElectricalangle0π/32π/3π

4π/35π/32πConductionsequenceACBACBC→BA→BA→CB→CB→AC→AV1TurnonV2TurnonV3TurnonV4TurnonV5TurnonV6TurnonTurnon10.3COMPARINGBLDCMOTORSTOOTHERMOTORTYPESComparedtobrushedDCmotorsandinductionmotors,BLDCmotorshavemanyadvantagesandfewdisadvantages.Brushlessmotorsrequirelessmaintenance,sotheyhavealongerlifecomparedwithbrushedDCmotors.BLDCmotorsproducemoreoutputpowerperfr