电机学（第七版）（修订版）课件 Chapter-3-Electromechanical-Energy-Conversion-Principles

Chapter3

Electromechanical-Energy-ConversionPrinciples7/10/2024ElectromechanicalEnergyConversion1IntroductionConversionofenergyfromelectricaltomechanicalformorfrommechanicaltoelectricalformthroughthemediumofelectricormagneticfieldsDevicesincludeTransducers(sensorsandspeakersForce-producingdevices(actuators)Continuousenergyconverters(motorsandgenerators)7/10/2024ElectromechanicalEnergyConversion23.1Forceandtorque

inmagnetic-fieldsystemsLorentzforcelawgivestheforceF[N]onachargeq[C]movingwithvelocityv[m/s]throughanelectricfieldE[V/m]andamagneticfluxdensityB[T]F=q(E+v×B)7/10/2024ElectromechanicalEnergyConversion3Right-handrulefordirectionofforceduetomagneticfield3.2EnergybalancemethodThismethodusesasimplerphysicalpicturebasedonenergyconservationDoesnotrequireddetailedfielddistributionsFocusesonthemostimportantforcesortorquesCanbeappliedeasilytopracticaldevicesEnergybalanceforamagnetic-fielddevice7/10/2024ElectromechanicalEnergyConversion4Signconventionisfor:electricalenergyinputandmechanicalenergyoutputInamotor,signswillbepositiveInagenerator,signswillbenegative7/10/2024ElectromechanicalEnergyConversion5SimpleenergyconversiondeviceEnergybalanceforadevice7/10/2024ElectromechanicalEnergyConversion63.3Energyinsinglyexcitedmagnetic-fieldsystemsAmagneticcircuitwithacoil,anairgap,andamovablesectionofthecoreThedeviceisanelectromagneticrelay7/10/2024ElectromechanicalEnergyConversion77/10/2024ElectromechanicalEnergyConversion8IntegrationpathsforWfldConservativesystemhasenergythatdoesnotdependontheparticularpathWeusepath2forevaluatingWfld7/10/2024ElectromechanicalEnergyConversion97/10/2024ElectromechanicalEnergyConversion103.4Determinationofmagneticforceandtorquefromenergy7/10/2024ElectromechanicalEnergyConversion11Forceortorque?Inatranslationalsystem,useforcefandpositionxInananalogousrotatingsystem,useTandangularpositionqTorqueisforcetimeradiusarm,tendingturnarotoraboutanaxis7/10/2024ElectromechanicalEnergyConversion123.5DeterminationofmagneticforcefromcoenergyAstatefunctionrelatedtoenergyiscalledcoenergyW’7/10/2024ElectromechanicalEnergyConversion13RemarksCoenergyisoftenconvenientsincecurrentisamoreeasilymeasuredthanfluxlinkageEitherformulation(energyorcoenergy)willgivethecorrectresults,ifusedcorrectlySeefigures3.10and3.11inthetexttoverifythattheygiveidenticalresults7/10/2024ElectromechanicalEnergyConversion143.6Multiplyexcitedmagnetic-fieldsystemsSystemswithmorethanonecoilarecalledmultiplyexcitedConsideradoublyexcitedrotatingsystem(twocoilsandtwoelectricalsources)butonerotatingshaft7/10/2024ElectromechanicalEnergyConversion157/10/2024ElectromechanicalEnergyConversion16Rememberthatpartialderivativesaretakenwithrespecttoonevariableasifallothervariableswereconstant7/10/2024ElectromechanicalEnergyConversion17IntegrationpathtoobtainfieldenergyforadoublyexcitedmagneticfieldsystemLinearmagneticcoreSpecialcaseoflinearmagnetics7/10/2024ElectromechanicalEnergyConversion18SystemswithpermanentmagnetsPermanent-magnetsystemswillneedspecialconsideration,sincetheenergyinthemagneticfieldwillbezeroonlyifthemagnetisdemagnetizedWemodelthisbyafictitiouswindingthathasacurrenttocounteractthefluxofmagnetforthepurposeoffindinganenergyexpression7/10/2024ElectromechanicalEnergyConversion197/10/2024ElectromechanicalEnergyConversion20Thefictitiouscurrentif=0atnormalconditions,butanonzerovalueonpath1atogivenomagneticforceonthatpath(theintegraliszeroonpath1a)Forsystemswithbothpermanentmagnetsandwindings:Useafictitiouscoiltoreplacethemagnet:(Ni)equiv=-H’cd7/10/2024ElectromechanicalEnergyConversion21Analysisnowproceedsasifthemagneticcircuithadtwocoils.Seeexample3.9fordetailsDynamicequations7/10/2024ElectromechanicalEnergyConversion22TheelectromagneticforceffldandtheinductanceL(x)arecalculatedbythemethodsdevelopedearlierTheequationsarenon-linearanddifficulttosolveSection3.9.1discussessimulationwithMATLAB/SimulinkSection3.9.2discusseslinearization(whichisequivalenttosmall-signalanalysis7/10/2024ElectromechanicalEnergyConversion23SummaryEnergyinanelectromechanicalsystemreliesoncouplingmagneticorelectricfieldWehavelookedatsingly-anddoubly-excitedmagneticfieldsystems,with