外文翻譯--直流電機(jī)速度控制.doc

SpeedControlofDCMotorRegulatorSystemsAregulatorsystemisonewhichnormallyprovidesoutputpowerinitssteady-stateoperation.Forexample,amotorspeedregulatormaintainsthemotorspeedataconstantvaluedespitevariationsinloadtorque.Eveniftheloadtorqueisremoved,themotormustprovidesufficienttorquetoovercometheviscousfrictioneffectofthebearings.Otherformsofregulatoralsoprovideoutputpower；Atemperatureregulatormustmaintainthetemperatureof,say,anovenconstantdespitetheheatlossintheoven.Avoltageregulatormustalsomaintainmustoutputvoltageconstantdespitevariationintheloadcurrent.Foranysystemtoprovideanoutput,e.g.,speed,temperature,voltage,etc,anerrorsignalmustexistundersteady-stateconditions.ElectricalBrakingInmanyspeedcontrolsystem,e.g.,rollingmillsminewinders,etc.,theloadhastobefrequentlybroughttoastandstillandreversed.Therateatwhichthespeedreducesfollowingareducedspeeddemandisdependentonthestoredenergyandthebrakingsystemused.Asmallspeedcontrolsystem(sometimesknownasavelodyne)canemploymechanicalbraking,butthisisnotfeasiblewithlargespeedcontrollerssinceitisdifficultandcostlytoremovetheheatgenerated.Thevariousmethodsofelectricalbrakingavaiableare:(1)Regenerativebraking.(2)Eddycurrentbraking.(3)Dynamicbraking.(4)Reversecurrentbraking(plugging).Regenerativebrakingisthebestmethod,thoughnotnecessarilythemosteconomic.Thestoredenergyintheloadisconvertedintoelectricalenergybytheworkmotor(actingtemporarilyasagenerator)andisreturnedtothepowersupplysystem.Thesupplysystemthusactsasa“sink”intowhichtheunwantedenergyisdelivered.Providingthesupplysystemhasadequatecapacity,theconsequentriseinterminalvoltagewillbesmallduringtheshortperiodsofregeneration.IntheWard-LeonardmethodofspeedcontrolofDCmotors,regenerativebrakingisinherent,butthyristordriveshavetobearrangedtoinverttoregenerate.Inductionmotordrivercanregenerateiftherotorshaftisdrivenfasterthanspeedoftherotatingfield.Theadventoflow-costvariablevariable-frequencysuppliesfromthyristorinvertershavebroughtaboutconsiderablechargesintheuseofinductionmotorsinvariablespeeddrives.Eddycurrentbrakingcanbeappliedtoanymachine,simplybymountingacopperoraluminiumdiscontheshaftandrotatingitinamagneticfield.Theproblemofremovingtheheatgeneratedissevereinlargesystemasthetemperatureoftheshaft,bearing,andmotorwillberaisedifprolongedbrakingisapplied.Indynamicbreaking,thestoredenergyisaresistorinthecircuit.WhenappliedtosmallDCmachines,thearmaturesupplyisdisconnectedandaresistorisconnectedacrossthearmature(usuallybyarelay,contactor,orthyristor).Thefieldvoltageismaintained,andbrakingisapplieddowntothelowestspeed.Inductionmotorsrequireasomewhatmorecomplexarrangement,thestatorwindingsbeingdisconnectedfromtheACsupplyandreconnectedtoaDCsupply.Theelectricalenergygeneratedisthendissipatedintherotorcircuit.DynamicbrakingisappliedtomanylargeAChoistsystemwherethebrakingdutyisbothsevereandprolonged.Anyelectricalmotorcanbebroughttoastandstillbysuddenlyreconnectingthesupplytoreversethedirectionofrotation(reversecurrentbraking).Appliedundercontrolledconditions,thismethodofbrakingissatisfactoryforalldrivers.Itsmajordisadvantageisthattheelectricalenergyconsumedbythemachinewhenbrakingisequaltothestoredenergyintheload.Thisincreasestherunningcostsignificantlyinlargedrives.EqualpulsewidthPWMlawVVVF(VariableVoltageVariableFrequency)installsintheearlytimeisusesPAM(PulseAmplitudeModulation)tocontrol,itsinventorpartwhichthetechnologyrealizesbutonlycanoutputthefrequencyadjustablesquare-wavevoltagenottobeabletoadjustthepressure.ThepulsewidthPWMlawarepreciselyinordertoovercome,isinthePWMlawwhichthePAMlawthisshortcomingdevelopmentcomesthesimplestonekind.ItiseachpulsewidthequalpulserowtookthePWMwave,throughachangepulserowcyclemaythefrequencymodulation,thechangepulsewidthorthedutyfactormayadjustthepressure,usesthesuitablecontrolmethodthentocausethevoltageandthefrequencycoordinationchange.IsoppositeinthePAMlaw,thismethodmeritsimplifiedtheelectriccircuitstructure,enhancedtheinputendpowerfactor,butsimultaneouslyalsohasintheoutputvoltagebesidesthefundamentalwave,butalsocontainsthebigharmoniccomponent.StochasticPWMThattimethehighefficiencytransistormainlyforthebipolarityDaringtontriode,thecarrierfrequencygenerallydidnotsurpass5kHz,thevibrationwhichtheelectricalmachinerywindingelectromagnetismnoiseandtheovertonecreatedhasarousedpeoplesinterest.Inordertoobtaintheimprovement,thestochasticPWMmethodarisesatthehistoricmoment.Itsprincipleisthestochasticchangeturn-onfrequencycausestheelectricalmachineryelectromagnetismnoisetobelimitedtoapproximatelythebeltwhitenoise(inlinearfrequencycoordinatesystem,variousfrequenciesenergydistributioniseven),althoughthenoiseadecibelnumberhasnotalwayschanged,butweakensgreatlytakethefixedturn-onfrequencyasthecharacteristiccolorednoiseintensity.Becauseofthis,evenifinIGBTbywidespreadapplicationtoday,hashadtolimitregardingthecarrierfrequencyiscomparingthelowfrequencythesituation,stochasticPWMstillhaditsspecialvalue；Ontheotherhandexplainedeliminatesthemachineryandtheelectromagnetismnoisebestmethodenhancestheoperatingfrequencyblindly,thestochasticPWMtechnologywaspreciselyprovidesananalysis,hassolvedthiskindofquestionbrand-newmentality.SpatialvoltagevectorcontrolPWMSpatialvoltagevectorcontrolPWM(SVPWM)alsocallsthemagneticfluxsinePWMlaw.Ittakethethree-phaseprofilewholeproductioneffectasthepremise,takeapproachestheelectricalmachineryairgaptheidealcircularrotaryfieldpathasthegoal,hastheactualmagneticfluxwiththeinventordifferentswitchpatterntoapproachthebasedirectorcirclemagneticflux,bytheirscomparisonresultdecidedtheinventortheswitch,formsthePWMprofile.Thislawembarksfromtheelectricmotorangle,regardsastheinventorandtheelectricalmachineryawhole,inscribesthepolygontoapproachthecirclethewaytocarryonthecontrol,causestheelectricalmachinerytoobtainthepeak-to-peakvalueconstantcircularmagneticfield(sinemagneticflux).Theconcretemethoddividesintothemagneticfluxsplit-ringtypeandthemagneticfluxclosedlooptype.Themagneticfluxsplit-ringlawsynthesizesanequivalentvoltagevectorwithatwonon-vanishingvectorsumnullvector,ifthesamplingtimeenoughissmall,maysynthesizetherandomvoltagevector.Whenthislawoutputratio-voltagesine-wavemodulationenhances15%close,sumoftheharmoniccurrenteffectivevaluesmallest.Themagneticfluxclosedlooptypeintroducesthemagneticfluxfeedback,controlsthemagneticfluxthesizeandthechangespeed.Estimatesthemagneticfluxafterthecomparisonandassignsthemagneticflux,accordingtotheerrordecidedhasthenextvoltagevector,formsthePWMprofile.Thismethodhasovercomethemagneticfluxsplit-ringmethodinsufficiency,whenhassolvedtheelectricalmachinerylowspeed,thestatorresistanceaffectsthemajorproblem,reducedtheelectricalmachinerypulsationandthenoise.Butbecausehasnotintroducedthetorquetheadjustment,thesystemperformancehasnothadthefundamentalimprovement.VectorControlPWMThevectorcontrolalsocalledthemagneticfielddirectiondetectioncontrol,itsprincipleisasynchronousmotorunderthree-phasecoordinatesystemstatorcurrentIa,IbandIc,throughthethree-phase/twophasetransformation,equivalentbecomesundertwostaticcoordinatesystemsalternatingcurrentIa1andIb1,againthroughpressestherotormagneticfielddirectiondetectionrevolvingtransformation,equivalentbecomesunderthesynchronizedrevolvingcoordinatesystemdirectcurrentIm1andIt1(Im1isequaltothedirectcurrentmotorexcitingcurrent；It1isequaltothearmatureelectriccurrentwhichisproportionalwiththetorque),thentheimitationdirectdischargemotivecontrolmethod,realizestothemotorcontrol.Itsessenceisthemotorequivalentisthedirectcurrentmotor,separatelytothespeed,themagneticfieldtwocomponentscarriesontheindependentcontrol.Throughth