电气工程专业毕业设计外文翻译文档格式.docx
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电气工程专业毕业设计外文翻译文档格式.docx
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ControlofInductionMachineDrives
6.1Introduction
6.2ScalarInductionMachineControl
6.3VectorControlofInductionMachines
VectorFormulationoftheInductionMachine•Induction
MachineDynamicModel•Field-OrientedControlofthe
InductionMachine•DirectTorqueControlofthe
InductionMachine
6.4Summary
Inductionmachineshavebecomethestapleforelectromechanicalenergyconversionintoday’sindustry;
theyareusedmoreoftenthanallothertypesofmotorscombined.Severalfactorshavemadethemthemachineofchoiceforindustrialapplicationsvs.DCmachines,includingtheirruggedness,reliability,andlowmaintenance[1,2].Thecage-inductionmachineissimpletomanufacture,withnorotorwindingsorcommutatorforexternalrotorconnection.Therearenobrushestoreplacebecauseofwear,andnobrusharcingtopreventthemachinefrombeingusedinvolatileenvironments.Theinductionmachinehasahigherpowerdensity,greatermaximumspeed,andlowerrotorinertiathantheDCmachine.
TheinductionmachinehasonesignificantdisadvantagewithregardtotorquecontrolascomparedwiththeDCmachine.Thetorqueproductionofagivenmachineisrelatedtothecross-productofthestatorandrotorflux-linkagevectors[3–5].Iftherotorandstatorfluxlinkagesareheldorthogonaltooneanother,theelectricaltorqueofthemachinecanbecontrolledbyadjustingeithertherotororstatorflux-linkageandholdingtheotherconstant.ThefieldandarmaturewindingsinaDCmachineareheldorthogonalbyamechanicalcommutator,makingtorquecontrolrelativelysimple.Withaninductionmachine,thestatorandrotorwindingsarenotfixedorthogonaltooneanother.Theinductionmachineissinglyexcited,withtherotorfieldinducedbythestatorfield,furthercomplicatingtorquecontrol.Untilafewyearsago,theinductionmachinewasmainlyusedforconstant-speedapplications.Withrecentimprovementsinsemiconductortechnologyandpowerelectronics,theinductionmachineisseeingwideruseinvariable-speedapplications[6].
ThischapterdiscusseshowthesechallengesrelatedtotheinductionmachineareovercometoeffecttorqueandspeedcontrolcomparablewiththatoftheDCmachine.Thefirstsectioninvolveswhatistermedvolts-per-hertz,orscalar,control.Thiscontrolmethodisderivedfromthesteady-statemachinemodelandissatisfactoryformanylow-performanceindustrialandcommercialapplications.Therestofthechapterwillpresentvector-controlledmethodsappliedtotheinductionmachine[7].Thesemethodsareaimedatbringingaboutindependentcontrolofthemachinetorque-andflux-producingstatorcurrents.Developedusingthedynamicmachinemodel,vector-controlledinductionmachinesexhibitfarbetterdynamicperformancethanthosewithscalarcontrol[8].
6.2ScalarInductionMachineControl
Inductionmachinescalarcontrolisderivedusingtheinductionmachinesteady-statemodelshowninFig.11.1[1].Thephasorformofthemachinevoltagesandcurrentsisindicatedbycapitalletters.Thestatorseriesresistanceandleakagereactanceareand,respectively.Thereferredrotorseriesresistanceandleakagereactanceareand,respectively.Themagnetizingreactanceis;
thecorelossduetoeddycurrentsandthehysteresisoftheironcoreisrepresentedbytheshuntresistance.Themachineslipsisdefinedas[1](11.1)
(6-1)
whereisthesynchronous,orexcitationfrequency,andisthemachineshaftspeed,bothinelectricalradians-per-second.Thepowersuppliedtothemachineshaftcanbeexpressedas
(6-2)
SolvingforandusingEq.(11.2),theshafttorquecanbeexpressedas
(6-3)
wherethenumeral3inthenumeratorisusedtoincludethetorquefromallthreephases.Thisexpressionmakesclearthatinductionmachinetorquecontrolispossiblebyvaryingthemagnitudeoftheappliedstatorvoltage.Thenormalizedtorquevs.slipcurvesforatypicalinductionmachinecorrespondingtovariousstatorvoltagemagnitudesareshowninFig.11.2.Speedcontrolisaccomplishedbyadjustingtheinputvoltageuntilthemachinetorqueforagivenslipmatchestheloadtorque.However,thedevelopedtorquedecreasesasthesquareoftheinputvoltage,buttherotorcurrentdecreaseslinearlywiththeinputvoltage.Thisoperationisinefficientandrequiresthattheloadtorquedecreasewithdecreasingmachinespeedtopreventoverheating[1,2].Inaddition,thebreakdowntorqueofthemachinedecreasesasthesquareoftheinputvoltage.Fansandpumpsareappropriateloadsforthistypeofspeedcontrolbecausethetorquerequiredtodrivethemvarieslinearlyorquadraticallywiththeirspeed.
LinearizationofEq.(11.3)withrespecttomachineslipyields
(6-4)
Thecharacteristictorquecurvecanbeshiftedalongthespeedaxisbychangingωewiththecapabilityfordevelopi
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