直流电机毕业论文中英文资料对照外文翻译文献

IntroductiontoD.C.MachinesD.C.machinesarecharacterizedbytheirversatility.Bymeansofvariouscombinationsofshunt-,series-,andseparatelyexcitedfieldwindingstheycanbedesignedtodisplayawidevarietyofvolt-ampereorspeed-torquecharacteristicsforbothdynamicandsteadystateoperation.Becauseoftheeasewithwhichtheycanbecontrolled,systemsofD.C.machinesareoftenusedinapplicationsrequiringawiderangeofmotorspeedsorprecisecontrolofmotoroutput.TheessentialfeaturesofaD.C.machineareshownschematically.Thestatorhassalientpolesandisexcitedbyoneormorefieldcoils.Theair-gapfluxdistributioncreatedbythefieldwindingissymmetricalaboutthecenterlineofthefieldpoles.Thisiscalledthefieldaxisordirectaxis.Asweknow,theA.C.voltagegeneratedineachrotatingarmaturecoilisconvertedtoD.C.intheexternalarmatureterminalsbymeansofarotatingcommutatorandstationarybrushestowhichthearmatureleadsareconnected.Thecommutator-brushcombinationformsamechanicalrectifier,resultinginaD.C.armaturevoltageaswellasanarmaturem.m.f.Wavethenis90electricaldegreesfromtheaxisofthefieldpoles,i.e.inthequadratureaxis.Intheschematicrepresentationthebrushesareshowninquadratureaxisbecausethisisthepositionofthecoilstowhichtheyareconnected.Thearmaturem.m.f.Wavethenisalongthebrushaxisasshown.(Thegeometricalpositionofthebrushesinanactualmachineisapproximately90electricaldegreesfromtheirpositionintheschematicdiagrambecauseoftheshapeoftheendconnectionstothecommutator.)Themagnetictorqueandthespeedvoltageappearingatthebrushesareindependentofthespatialwaveformofthefluxdistribution;forconvenienceweshallcontinuetoassumeasinusoidalflux-densitywaveintheairgap.Thetorquecanthenbefoundfromthemagneticfieldviewpoint.Thetorquecanbeexpressedintermsoftheinteractionofthedirect-axisair-gapfluxperpoledandspace-fundamentalcomponent1Faofthearmaturem.m.f.wave.Withthebrushesinthequadratureaxistheanglebetweenthesefieldsis90electricaldegrees,anditssineequalsunity.ForaPpolemachine2122dPTFa（1-1）Inwhichtheminussigngasbeendroppedbecausethepositivedirectionofthetorquecanbedeterminedfromphysicalreasoning.Thespacefundamental1Faofthesawtootharmaturem.m.f.waveis28timesitspeak.Substitutioninaboveequationthengives()2aaaPCTiNmm（1-2）Where,aI=currentinexternalarmaturecircuit;aC=totalnumberofconductorsinarmaturewinding;m=numberofparallelpathsthroughwinding.And2aaPCKm（1-3）isaconstantfixedbythedesignofthewinding.Therectifiedvoltagegeneratedinthearmaturehasalreadybeendiscussedbeforeforanelementarysingle-coilarmature.Theeffectofdistributingthewindinginseveralslotsisshowninfigure.Inwhicheachoftherectifiedsinewaveisthevoltagegeneratedinoneofthecoils,commutationtakingplaceatthemomentwhenthecoilsidesareintheneutralzone.Thegeneratedvoltageasobservedfromthebrushesandisthesumoftherectifiedvoltagesofallthecoilsinseriesbetweenbrushesandisshownbytheripplinglinelabeledaeinfigure.Withadozenorsocommutatorsegmentsperpole,theripplebecomesverysmallandtheaveragegeneratedvoltageobservedfromthebrushesequalsthesumoftheaveragevaluesoftherectifiedcoilvoltages.Therectifiedvoltageaebetweenbrushes,Knownalsoasthespeedvoltage,is2aadmadmPCeKm（1-4）whereaKisthedesignconstant.Therectifiedvoltageofadistributedwindinghasthesameaveragevalueasthatofaconcentratedcoil.Thedifferenceisthattherippleisgreatlyreduced.Fromtheaboveequations,withallvariableexpressedinSIunits,aameiT（1-5）Thisequationsimplysaysthattheinstantaneouspowerassociatedwiththespeedvoltageequalstheinstantaneousmechanicalpowerwiththemagnetictorque.Thedirectionofpowerflowbeingdeterminedbywhetherthemachineisactingasamotororgenerator.Thedirect-axisair-gapfluxisproducedbythecombinedm.m.f.ffNiofthefieldwindings.Theflux-m.m.f.Characteristicbeingthemagnetizationcurvefortheparticularirongeometryofthemachine.Inthemagnetizationcurve,itisassumedthatthearmature–m.m.f.Waveisperpendiculartothefieldaxis.Itwillbenecessarytoreexaminethisassumptionlaterinthischapter,wheretheeffectsofsaturationareinvestigatedmorethoroughly.Becausethearmaturee.m.f.isproportionaltofluxtimesspeed,itisusuallymoreconvenienttoexpressthemagnetizationcurveintermsofthearmaturee.m.f.0aeataconstantspeed0m.Thevoltageaeforagivenfluxatanyotherspeedmisproportionaltothespeed,i.e.00maamee（1-6）Thereisthemagnetizationcurvewithonlyonefieldwindingexcited.Thiscurvecaneasilybeobtainedbytestmethods,noknowledgeofanydesigndetailsbeingrequired.Overafairlywiderangeofexcitationthereluctanceoftheironisnegligiblecomparedwiththatoftheairgap.Inthisregionthefluxislinearlyproportionaltothetotalm.m.f.ofthefieldwindings,theconstantofproportionalitybeingthedirect-axisair-gappermeance.TheoutstandingadvantagesofD.C.machinesarisefromthewidevarietyofoperatingcharacteristicsthatcanbeobtainedbyselectionofthemethodofexcitationofthefieldwindings.ThefieldwindingsmaybeseparatelyexcitedfromanexternalD.C.source,ortheymaybeself-excited;i.e.themachinemaysupplyitsownexcitation.Themethodofexcitationprofoundlyinfluencesnotonlythesteady-statecharacteristics,butalsothedynamicbehaviorofthemachineincontrolsystems.Theconnectiondiagramofaseparatelyexcitedgeneratorisgiven.Thereq