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PowerElectronicsinMotorDrives:WhereisitNagarajanSridharProductMarketingManagerHighPerformanceIsolatedPowerSolutionsPowerManagementTexasInstrumentsPowerElectronicsinMotorDrives:Whereisit2October2019WhatisamotordriveAnelectricmotorisadevicethatconvertselectricalenergytomechanicalenergy.
Italsocanbeviewedasadevicethattransfersenergyfromanelectricalsourcetoamechanicalload.
Thesysteminwhichthemotorislocatedandmakesitspiniscalledthedrive,alsoreferredtoastheelectricdriveormotordrive.
Thefunctionofthemotordriveistodrawelectricalenergyfromtheelectricalsourceandsupplyelectricalenergytothemotor,suchthatthedesiredmechanicaloutputisachieved.
Typically,thisisthespeedofthemotor,torque,andthepositionofthemotorshaft.
Figure1showstheblockdiagramofamotordrive.
Motordriveshaveanundeniablepresenceinkeysystemsusedinourdailylives.
Assuch,energysavingsthroughefficiencyandreliabilityimprovementisofparamountimportanceandisthekeyfocusforsuppliersandregulatorystandardsbodies.
Everydayweseesystemsinmotionallaroundus.
WhatmakesthemmoveOntheoutset,itmaybeduetowheelsasinthecaseofanautomobile.
Whatactuallydrivesthesemovements,though,aremotors.
Additionally,manyhouseholdappliancessuchrefrigerators,air-conditioners,ventilationfans,washers,driersandsomanyothersallrequireelectricmotors.
Onecanseethatmotorsarepartofourday-to-daylife.
Thegoalofthispaperistodiscusstheroleofpowerelectronics–thevariouscomponentsandrequirements–inmotordrivesthroughapplicationsthatweuseandencounterinhouseholdandindustrialenvironments.
Figure1.
Blockdiagramofamotordrivesystem.
MotorDriveMotorElectricalSourcePowerConverterMechanicalLoadSensorControllerPowerElectronicsinMotorDrives:Whereisit3October2019Thefunctionsofthepowerconvertercircuitinthemotordriveare:Transferelectricalenergyfromasourcethatcouldbeofagivenvoltage,currentatacertainfrequencyandphaseastheinputToanelectricaloutputofdesiredvoltage,current,frequencyandphasetothemotorsuchthattherequiredmechanicaloutputofthemotorisachievedtodrivetheloadControllerregulatesenergyflowthroughfeedbackcomingfromthesensorblockSignalsmeasuredbysensorsfromthemotorarelow-power,whicharethensenttothecontrollerControllertellstheconverterwhatitneedstobedoing.
Aclosed-loopfeedbacksystemisthemethodofcomparingwhatisactuallyhappeningtowhatthemotorshouldbeoutputting,thenadjustingtheoutputaccordinglytomaintainthetargetoutputMotordriveefficiencyElectricmotorsrepresent45percentofallelectricalenergyconsumptionacrossallapplications.
Increasingtheefficiencyofmotor-drivesystemscouldpotentiallyresultinasignificantreductioninglobalelectricityconsumption[1].
Withincreasingdemandofelectricityalongwithindustrializationandurbanizationacrosstheglobe,theabilitytosupplyenergyisbecomingevenmorechallenging.
Aspartofaglobalefforttoreduceenergyconsumptionandcarbonemissionsontheenvironment,variousregulationsacrossmanycountrieshaveputforthandarecontinuallyworkingongovernmentalmandatestoimprovemotordriveefficiency.
Alltheserequirementsmakeitcompellingtohaveanefficientpowerconvertersystemusingswitched-modepowersupplies(SMPS).
TheSMPSusessemiconductorpowerswitches(alsocalledpowerelectronicswitches)inaswitchmodeandonandoffstatesonly,thatyields100percentefficiencyinanidealsituation.
Powerelectronicssystemsareprimarilydesignedusingsilicon-basedpowermanagementwithpowersemiconductorswitches.
TheseswitchesarepowerMOSFETs,bipolarjunctiontransistors(BJTs),andisolatedgatebipolartransistors(IGBTs)thathavemadesignificantimprovementsintheirperformances.
Examplesincludeloweron-stateresistance,increasedblockingvoltage,andhigherdrivecurrents.
Furthermore,alotofdevelopmentistakingplaceusingwide-band-gapsemiconductorssuchassiliconcarbide(SiC).
SiCisofparticularinteresttomotordrivesthattransferveryhighpowerathigh-voltagelevels.
MotordriveclassificationsBeforewedelveintomotordriveapplicationsandtheroleofpowerelectronicsinthesesystems,hereisaquickoverviewonhowmotordrivesareclassified(Figure2).
BrushedMotorsBrushlessMotorsInductionMotorsPMSM*MotorsElectricalMotorsDCMotorsACMotorsFigure2.
Classificationofmotors.
*PMSM=permanentmagnetsynchronousmotors.
PowerElectronicsinMotorDrives:Whereisit4October2019Table1summarizeswhereAC(induction)andDC(brushedandbrushless)motorsareusedintermsofvoltageandpowerlevels,alongwiththeprosandconsofeach.
PowerconverterinmotordrivesThedriveconfigurationformotorssummarizedinTable1aregenerallythesame.
However,whatdiffersisthepowerconvertertopologyinthepowerconvertercircuit.
SincethebulkoftheseapplicationsaremovingtowardsbrushlessDC(BLDC)orinductionmotors,ourfocuswillbeonapplicationsthatusethesetwotypesofmotors.
Ingeneral,selectingamotordrivemayrequirelookingatthepowerandvoltagelevelswhileaddressingquestionsthatdependontheapplication.
Examplescouldbethestartingtorque,loadinertia,patternofoperation,environmentalconditions,orthemotor'sabilitytoregenerate.
Addressingthesequestionsisoutsidethescopeofthispaper.
ACmotordrivesTheACmotordrive,asthenamesuggests,requiresanACinputtotheinductionmotorusedtodrivelargeindustrialloadssuchasHVACforcommercialbuildings–pumpsandcompressors,factoryautomation,industrialequipmentthatrequiresprovisionsforspeedadjustmentssuchasconveyorbelts,tunnelboring,mining,papermills,andmanyothers.
AnACmotordrivetakesanACenergysource,rectifiesittoaDCbusvoltageand,implementingcomplexcontrolalgorithms,invertstheDCbacktoACintothemotorusingcomplexcontrolalgorithmsbasedonloaddemand.
Figure3showsablockdiagramofanACmotordrive.
Thepowerstageandpowersuppliesaremarkedinteal.
PowerstageThepowerconvertertopologyusedinthepowerstageisthatofathree-phaseinverterwhichtransferspowerintherangeofkWtoMW.
InvertersconvertDCtoACpower.
TypicalDCbusvoltagelevelsare600Vto1200V.
Consideringthehighpowerandvoltagelevels,thethree-phaseinverterusessixisolatedgatedrivers(Figure3).
Eachphaseusesahigh-sideandlow-sideinsulatedgatebipolartransistor(IGBT)switch.
Operatingusuallyinthe20-kHzto30-kHzrange,eachphaseappliespositiveandnegativehigh-voltageDCpulsestothemotorwindingsinanalternatingmode.
High-powerIGBTrequiresisolatedgatedriverstocontroltheiroperations.
EachIGBTisdrivenbyasingleisolatedgatedriver.
Theisolationisgalvanicbetweenthehigh-voltageoutputofthegatedriverandthelow-voltagecontrolinputsthatcomefromthecontroller.
TheemitterofthetopIGBTfloats,whichnecessitatesusinganisolatedgate-driver.
Inordertoisolateahigh-voltagecircuitwiththatofalow-voltagecontrolcircuit,isolatedgate-driversareusedtocontrolthebottomIGBTs.
MotorTypeVoltageLevelsPowerLevelsApplicationsAdvantagesDisadvantagesBrushedDC600V>750WIndustrialandfactoryautomationLowcost,lessmaintenance,rugged,reliableinwidepowerrangeStartingissues,low-powerfactorcorrection,complicatedspeedcontrolTable1.
Comparativeanalysisofmotors.
PowerElectronicsinMotorDrives:Whereisit5October2019Gatedriversconvertthepulse-widthmodulation(PWM)signalsfromthecontrollerintogatepulsesfortheFETsorIGBTs.
Moreover,thesegatedriversneedtohaveintegratedprotectionfeaturessuchasdesaturation,activeMillerclamping,softturn-offandsoon.
Theseisolatedgatedriversusuallysufferfromlowdrivestrength,especiallywhenthedrivecurrentcapabilityisbelowthe2Arange.
Traditionally,thesedriveapplicationsusediscretecircuitstoboostthedrivecurrent.
Recently,therehavebeenseveralgatedriverICsdevelopedtoreplacethediscretesolution.
Figure4illustratesthistrend.
InordertotakeadvantageofthelowconductionlossesinIGBTs,gatedriversneedtooperateatvoltagesmuchhigherthantheirthresholdvoltageintherangeof15Vto18V.
Furthermore,anIGBTisaminority-carrierdevicewithhighinputimpedanceandlargebipolarcurrent-carryingcapability.
TheswitchingcharacteristicsofanIGBTaresimilartothatofapowerMOSFET.
Foragivenconditionwhenturnedon,theIGBTbehavesmuchliketoapowerMOSFET,showingsimilarcurrentriseandvoltagefalltimes.
However,theswitchingcurrentduringturn-offisdifferent.
Attheendoftheswitchingevent,theIGBThasa"tailcurrent"thatdoesnotexistfortheMOSFET.
Thistailiscausedbyminoritycarrierstrappedinthe"base"ofthebipolaroutputsectionoftheIGBT.
ThiscausestheIGBTtoremainturnedon.
Unlikeabipolartransistor,itisnotpossibletoextractthesecarrierstospeedupswitching,asthereisnoexternalconnectiontothebasesection.
Therefore,thedeviceremainsturnedonuntilthecarriersrecombine.
Thistailcurrentincreasestheturn-offlosswhichrequiresanincreaseinthedeadtimebetweentheconductionoftwodevicesforagivenphaseofahalf-bridgecircuit.
Figure3.
BlockdiagramofanACmotordrive.
PositionFeedbackCommunicationInterface24VDCSystemPowerBus100to1200VLinePowerCommunicationOff-linePowerSupplyAC/DC(optional)IndustrialEthernetPHYIndustrial485PHYIndustrialCANPHYIndustrialEthernetPHYIndustrial485PHYIndustrialCANPHYMCUControl(withFieldbusIntegration)MotorDriveControlMCUInternalADCsPRUVREFSARADCSafetyMCUPROTDC/DCConverters&LDOsIsolatedDC/DCPowerStagePhase/VoltageFeedback(options)OPASensorsSDMIGBTsEncoderIsolatedGateDriversOPAAMPPowerElectronicsinMotorDrives:Whereisit6October2019Havinganegativevoltage(–5Vto–10V)atthegatehelpstoreducetheturn-offtimebyhelpingtorecombinethetrappedcarriers.
WhentheIGBTisturnedonthehighdv/dtandparasiticcapacitancebetweengateandemittergeneratesvoltagespikesacrossthegateterminal.
Thesespikescancauseafalseturn-onofthebottomIGBT.
Havinganegativevoltageatthegatehelpstoavoidthisfalseturn-ontrigger.
Usually15Vto18Visappliedtothegatetoturn-onthedeviceandanegativevoltageof–5Vto–8VisappliedtoturnofftheIGBT.
ThisrequirementiskeytodeterminethepowersupplyratingtotheIGBTdriver.
Typically,suchapowersupplyisaPWMcontrollerwithatopologythathastheabilitytoscaletheoutputpowerwhiledrivingthesehigh-powerIGBTs.
Typicalinputsforthesepowersuppliesareregulatedto24V(tobeexplainedshortly).
Oneexampleofaclassictopologyusedforthispowersupplyisthepush-pullisolatedconverter.
Thistopologyissimilartoaforwardconverterwithtwoprimarywinding.
Theadvantagethatpush-pullconvertershaveoverfly-backandforwardconvertersisthattheycanbescaleduptohigherpowers,inadditiontohigherefficiency.
MoredetailsandconstructionofthistopologywithapushpullconvertercanbefoundintheTIdesignguide[2].
PowerFETtrendsinMotorDrivesSiliconCarbide(SiC)MOSFETsaregainingtractioninthepowerstageformotordrives.
IGBTsandSiCMOSFETs,areagoodfitinhigh-powerACpowerstageapplicationsduetotheirhighvoltageratingsandhighcurrentratings.
SiCMOSFETshoweverdifferfromIGBTsintheswitchingfrequencyrequirement.
IGBTstypicallyoperateinthelowerswitchingfrequencyrange(5kHzto20kHz)whereasSiCMOSFETsoperateatamuchhigherswitchingfrequencyrange(50kHzto+300kHz).
Theabilitytoswitchathigherfrequenciesallowssystembenefitssuchashigherpowerdensity,higherefficiencyandlowerheatdissipation.
Asswitchingfrequencyrequirementsincrease,itisMicrocontrollerGateDriverICforCurrentBoostMicrocontrollerIsolatedGateDriverGateDriverGateDriverGateDriverGateDriverGateDriverM12345CGateDriverFigure4.
Three-phaseinvertertopologywithboostgatedriverpowersuppliesforIGBTgatedriversinthepowerstage.
PowerElectronicsinMotorDrives:Whereisit7October2019criticaltoselectagatedriverwithhighCMTIrating.
Highpowerswitchesareabletochangevoltageandcurrentwithinhundredsofnanoseconds.
Thisgeneratesverylargevoltagetransients,commonly>100V/ns.
Thegatedriverexperiencesthesevoltageswingsateveryswitchinginstant,particularlywhenthedriverisreferencedtotheswitchnode.
Itisimportantthatthegatedriverbeabletowithstandtheselargevoltagetransientstopreventnoisecouplingbacktotheprimarysideofthegatedrivertopreventfalsetriggersonthegatedrivelogic.
Theapplicationnote,"CommonmodetransientimmunityforIsolatedgatedrivers"providesmoredetailsonCMTI.
OtherpowersuppliesFigure3showsanofflinepowersupplythatdrawspowerfromthethree-phaseuniversalAClinetoaregulated24-VDCoutput.
Becauseofthelow-powerlevel(below75W),powerfactorcorrection(PFC)isnotneeded.
Theseofflinepowersuppliesaretypicallyfly-backtopologyconverterICsthatcouldbeacontrollerwithexternalMOSFET,oranintegratedMOSFETcontrollerorswitcher.
ThechoiceofthepowersupplyICisflexibleandisinfluencedbythepowerlevel,numberofoutputs,andaccuracyoftheregulation.
Thisofflinepowersupplyisusuallyaseparatemodule.
The24-VDCoutputisthesystempowerbusintheACmotordrivesystemthatisinputintothebiaspowersupplyforthepowerstageandnon-isolatedDC/DCconverter.
Thisnon-isolatedDC/DCregulatorfromthe24-Vsystemprovidespowertothecontroller,communicationsandsafetymicrocontrollers,interfacetransceivers,anddataconverters.
PowerstageABLDCpowerstageisalsoaninvertersimilartoanACmotordrive,exceptthattheinputcanbesingle-orthree-phases.
DC-railvoltagesaretypically48Vto600V,dependingonthepowerlevels.
TheswitchisusuallyapowerMOSFETswitchingataround100kHz.
Gatedriversarehigh-side,low-sideorhalf-bridgedriversperinverterphasewithnoisolationrequirement.
ProtectionfeaturesarenotascriticalasthoseneededfortheACmotordrive,exceptfordead-timecontroltoavoidshoot-throughsincethehigh-sideandlow-sidedriversareoperatingfromoneIC.
PowersuppliesBiaspowertothecontrollerandgatedriverscomesoffaregulatedpowersupplyfromthebattery.
Atypicalbatteryusedinthisspaceisthe18-VnominalLithium-Ion(Li-Ion)five-cellbattery.
Sincethesearecordlesstools,awallchargerisrequiredtochargethedrillperiodically.
Typically,chargingintherangeof50Wto1000Wisdoneusinganisolatedcontrollerthatistopology-specific,dependingonthepowerlevel.
Also,PFCisgenerallynotneededunlessthepowerlevelisinthefewhundredW.
Typicalchargingcontrollersarebasedoffofafly-back,interleavedfly-back,orpush-pulltopologies.
SummaryMotordrivesarebecomingmoreefficientaspowerelectronicdevicessuchaspowerswitches(IGBTsandMOSFETs),gatedriversandbiassuppliesarebeingincorporated.
Wediscussedtwokeyandpopularmotordrivesystems:ACandBLDC,andcoveredthefunctionalitiesandroleofgatedrivecircuitsandassociatedbiassupplies.
Keyareassuchasisolation,voltagelevelsandprotectionfeatureswerehighlighted.
TIhasseveralgatedriversforACdrives,theopto-emulateddriverUCC23513andthevoltageinputbasedisolatedgatedriverUCC53xxaswellastheISO545x/ISO585xfamiliesofdevices.
ForbrushlessDCdrivesusingthethree-phasepre-drivers,TIofferstheDRV8301/2/3/8,orsingle-phase,high-side/low-sidedriverssuchastheUCC272xxandLM510xfamilies.
Todrive100VpowerMOSFETssuchastheCSD19534Q5Aor80VCSD19501KCS,TIofferstheUCC27211A/UCC27201A,LM5105,LM5109andtheUCC272201A-Q1(forautomotiveapplications).
Regardlessofdrives,TIoffersavarietyofPWMcontrollersforbiassuppliessuchasUCC287xx,UCC28910,LM5030andLM5023.
References1.
Energy-EfficiencyPolicyOpportunitiesforElectricMotor-DrivenSystems,InternationalEnergyAgency,20112.
IsolatedIGBTgate-drivepush-pullpowersupplywith4outputs(TIDA-00181),TexasInstruments3.
Downloadthesedatasheets:CSD19534Q5A,CSD19501KCS,DRV8301,DRV8302,DRV8303,DRV8308,ISO5500,ISO5452,ISO5852S,LM5023,LM5030,LM5105,LM5109,UCC27211A,UCC27201A,UCC27531,UCC28710,UCC28910,UCC23513,UCC5320SLYY078A2019TexasInstrumentsIncorporatedTheplatformbarisatrademarkofTexasInstruments.
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