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外文翻译--直流电机速度控制.doc

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外文翻译--直流电机速度控制.doc

SpeedControlofDCMotorRegulatorSystemsAregulatorsystemisonewhichnormallyprovidesoutputpowerinitssteadystateoperation.Forexample,amotorspeedregulatormaintainsthemotorspeedataconstantvaluedespitevariationsinloadtorque.Eveniftheloadtorqueisremoved,themotormustprovidesufficienttorquetoovercometheviscousfrictioneffectofthebearings.OtherformsofregulatoralsoprovideoutputpowerAtemperatureregulatormustmaintainthetemperatureof,say,anovenconstantdespitetheheatlossintheoven.Avoltageregulatormustalsomaintainmustoutputvoltageconstantdespitevariationintheloadcurrent.Foranysystemtoprovideanoutput,e.g.,speed,temperature,voltage,etc,anerrorsignalmustexistundersteadystateconditions.ElectricalBrakingInmanyspeedcontrolsystem,e.g.,rollingmillsminewinders,etc.,theloadhastobefrequentlybroughttoastandstillandreversed.Therateatwhichthespeedreducesfollowingareducedspeeddemandisdependentonthestoredenergyandthebrakingsystemused.Asmallspeedcontrolsystemsometimesknownasavelodynecanemploymechanicalbraking,butthisisnotfeasiblewithlargespeedcontrollerssinceitisdifficultandcostlytoremovetheheatgenerated.Thevariousmethodsofelectricalbrakingavaiableare1Regenerativebraking.2Eddycurrentbraking.3Dynamicbraking.4Reversecurrentbrakingplugging.Regenerativebrakingisthebestmethod,thoughnotnecessarilythemosteconomic.Thestoredenergyintheloadisconvertedintoelectricalenergybytheworkmotoractingtemporarilyasageneratorandisreturnedtothepowersupplysystem.Thesupplysystemthusactsasasinkintowhichtheunwantedenergyisdelivered.Providingthesupplysystemhasadequatecapacity,theconsequentriseinterminalvoltagewillbesmallduringtheshortperiodsofregeneration.IntheWardLeonardmethodofspeedcontrolofDCmotors,regenerativebrakingisinherent,butthyristordriveshavetobearrangedtoinverttoregenerate.Inductionmotordrivercanregenerateiftherotorshaftisdrivenfasterthanspeedoftherotatingfield.Theadventoflowcostvariablevariablefrequencysuppliesfromthyristorinvertershavebroughtaboutconsiderablechargesintheuseofinductionmotorsinvariablespeeddrives.Eddycurrentbrakingcanbeappliedtoanymachine,simplybymountingacopperoraluminiumdiscontheshaftandrotatingitinamagneticfield.Theproblemofremovingtheheatgeneratedissevereinlargesystemasthetemperatureoftheshaft,bearing,andmotorwillberaisedifprolongedbrakingisapplied.Indynamicbreaking,thestoredenergyisaresistorinthecircuit.WhenappliedtosmallDCmachines,thearmaturesupplyisdisconnectedandaresistorisconnectedacrossthearmatureusuallybyarelay,contactor,orthyristor.Thefieldvoltageismaintained,andbrakingisapplieddowntothelowestspeed.Inductionmotorsrequireasomewhatmorecomplexarrangement,thestatorwindingsbeingdisconnectedfromtheACsupplyandreconnectedtoaDCsupply.Theelectricalenergygeneratedisthendissipatedintherotorcircuit.DynamicbrakingisappliedtomanylargeAChoistsystemwherethebrakingdutyisbothsevereandprolonged.Anyelectricalmotorcanbebroughttoastandstillbysuddenlyreconnectingthesupplytoreversethedirectionofrotationreversecurrentbraking.Appliedundercontrolledconditions,thismethodofbrakingissatisfactoryforalldrivers.Itsmajordisadvantageisthattheelectricalenergyconsumedbythemachinewhenbrakingisequaltothestoredenergyintheload.Thisincreasestherunningcostsignificantlyinlargedrives.EqualpulsewidthPWMlawVVVFVariableVoltageVariableFrequencyinstallsintheearlytimeisusesPAMPulseAmplitudeModulationtocontrol,itsinventorpartwhichthetechnologyrealizesbutonlycanoutputthefrequencyadjustablesquarewavevoltagenottobeabletoadjustthepressure.ThepulsewidthPWMlawarepreciselyinordertoovercome,isinthePWMlawwhichthePAMlawthisshortcomingdevelopmentcomesthesimplestonekind.ItiseachpulsewidthequalpulserowtookthePWMwave,throughachangepulserowcyclemaythefrequencymodulation,thechangepulsewidthorthedutyfactormayadjustthepressure,usesthesuitablecontrolmethodthentocausethevoltageandthefrequencycoordinationchange.IsoppositeinthePAMlaw,thismethodmeritsimplifiedtheelectriccircuitstructure,enhancedtheinputendpowerfactor,butsimultaneouslyalsohasintheoutputvoltagebesidesthefundamentalwave,butalsocontainsthebigharmoniccomponent.StochasticPWMThattimethehighefficiencytransistormainlyforthebipolarityDaringtontriode,thecarrierfrequencygenerallydidnotsurpass5kHz,thevibrationwhichtheelectricalmachinerywindingelectromagnetismnoiseandtheovertonecreatedhasarousedpeoplesinterest.Inordertoobtaintheimprovement,thestochasticPWMmethodarisesatthehistoricmoment.Itsprincipleisthestochasticchangeturnonfrequencycausestheelectricalmachineryelectromagnetismnoisetobelimitedtoapproximatelythebeltwhitenoiseinlinearfrequencycoordinatesystem,variousfrequenciesenergydistributioniseven,althoughthenoiseadecibelnumberhasnotalwayschanged,butweakensgreatlytakethefixedturnonfrequencyasthecharacteristiccolorednoiseintensity.Becauseofthis,evenifinIGBTbywidespreadapplicationtoday,hashadtolimitregardingthecarrierfrequencyiscomparingthelowfrequencythesituation,stochasticPWMstillhaditsspecialvalueOntheotherhandexplainedeliminatesthemachineryandtheelectromagnetismnoisebestmethodenhancestheoperatingfrequencyblindly,thestochasticPWMtechnologywaspreciselyprovidesananalysis,hassolvedthiskindofquestionbrandnewmentality.SpatialvoltagevectorcontrolPWMSpatialvoltagevectorcontrolPWMSVPWMalsocallsthemagneticfluxsinePWMlaw.Ittakethethreephaseprofilewholeproductioneffectasthepremise,takeapproachestheelectricalmachineryairgaptheidealcircularrotaryfieldpathasthegoal,hastheactualmagneticfluxwiththeinventordifferentswitchpatterntoapproachthebasedirectorcirclemagneticflux,bytheirscomparisonresultdecidedtheinventortheswitch,formsthePWMprofile.Thislawembarksfromtheelectricmotorangle,regardsastheinventorandtheelectricalmachineryawhole,inscribesthepolygontoapproachthecirclethewaytocarryonthecontrol,causestheelectricalmachinerytoobtainthepeaktopeakvalueconstantcircularmagneticfieldsinemagneticflux.Theconcretemethoddividesintothemagneticfluxsplitringtypeandthemagneticfluxclosedlooptype.Themagneticfluxsplitringlawsynthesizesanequivalentvoltagevectorwithatwononvanishingvectorsumnullvector,ifthesamplingtimeenoughissmall,maysynthesizetherandomvoltagevector.Whenthislawoutputratiovoltagesinewavemodulationenhances15close,sumoftheharmoniccurrenteffectivevaluesmallest.Themagneticfluxclosedlooptypeintroducesthemagneticfluxfeedback,controlsthemagneticfluxthesizeandthechangespeed.Estimatesthemagneticfluxafterthecomparisonandassignsthemagneticflux,accordingtotheerrordecidedhasthenextvoltagevector,formsthePWMprofile.Thismethodhasovercomethemagneticfluxsplitringmethodinsufficiency,whenhassolvedtheelectricalmachinerylowspeed,thestatorresistanceaffectsthemajorproblem,reducedtheelectricalmachinerypulsationandthenoise.Butbecausehasnotintroducedthetorquetheadjustment,thesystemperformancehasnothadthefundamentalimprovement.VectorControlPWMThevectorcontrolalsocalledthemagneticfielddirectiondetectioncontrol,itsprincipleisasynchronousmotorunderthreephasecoordinatesystemstatorcurrentIa,IbandIc,throughthethreephase/twophasetransformation,equivalentbecomesundertwostaticcoordinatesystemsalternatingcurrentIa1andIb1,againthroughpressestherotormagneticfielddirectiondetectionrevolvingtransformation,equivalentbecomesunderthesynchronizedrevolvingcoordinatesystemdirectcurrentIm1andIt1Im1isequaltothedirectcurrentmotorexcitingcurrentIt1isequaltothearmatureelectriccurrentwhichisproportionalwiththetorque,thentheimitationdirectdischargemotivecontrolmethod,realizestothemotorcontrol.Itsessenceisthemotorequivalentisthedirectcurrentmotor,separatelytothespeed,themagneticfieldtwocomponentscarriesontheindependentcontrol.Throughthecontrolrotorfluxlinkage,thenthedecompositionstatorcurrentobtainsthetorqueandthemagneticfieldtwocomponents,aftercoordinatetransformation,realizationorthogonalordecouplingcontrol.But,becausetherotorfluxlinkageaccuratelyobserveswithdifficulty,aswellasthevectortransformationcomplexity,causestheactualcontroleffectoftenwithdifficultytoachievetheoreticalanalysiseffect,thisisthevectorcontroltechnologyinthepracticeinsufficiency.Inaddition,Itmustdirectlyorindirectlyobtainstherotorfluxlinkagetobeabletorealizethestatorcurrentdecouplingcontrolinspaceposition,needstodisposetherotorpositionorthevelocitygeneratorinthiskindofvectorcontrolsystem,thisgivesmanyapplicationsituationstobringinconvenientlyobviously.TheanalyticalfunctionsofthearmaturereactionofpermanentmagnetbrushlessDCmotorwithconcentratedcoilsareproposedbyusingthemethodofimage,

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