Robust Control of an Induction Motor Drive Automat

RobustControlofanInductionMotorDriveHenrikMosskullTRITA–EE2006:008ISSN1653-5146ISBN91-7178-309-1AutomaticControlSchoolofElectricalEngineeringRoyalInstituteofTechnology(KTH)Stockholm,Sweden,2006SubmittedtotheSchoolofElectricalEngineering,RoyalInstituteofTechnology,inpartialfulfillmentoftherequirementsforthedegreeofDoctorofPhilosophy.Copyright©2006byHenrikMosskullRobustControlofanInductionMotorDriveAutomaticControlSchoolofElectricalEngineeringRoyalInstituteofTechnology(KTH)SE-10044Stockholm,SwedenAbstractThisthesisconsidersrobustcontrolofaninductionmotordrive,consistingofaninputfilter,avoltagesourceinverterandoneorseveralinductionmotorsinparallel.ThemotortorqueisherecontrolledbyusingthemethodIndirectSelfControl(ISC),andpoweroscillationsbetweentheinverterandtheinputfilteraredampedbymeansofastabilizationcontrollerinanouterfeedbackloop.Closed-loopperformancewithISCisanalyzedundertheassumptionofastiffinverterinputvoltage.Itisshownhowparametererrorsinfluencethetorqueloopandtheconclusionisthatthemotorleakageinductanceshouldnotbeoverestimated,especiallynotwithalargedesiredcontrolbandwidth.Itisalsoshownthatmodelerrorsenhancecrosscoupling,butthattheperformanceisquiteinsensitiveeventolargeparametricerrors.Basedontheclosed-loopmodel,expressionsforthecontrollerparametersarederivedtoobtainrequiredstabilitymargins.Fordesignofthestabilizationcontrollertosuppressoscillationsbetweentheinverterandtheinputfilter,itisshownthattheeffectsoftimedelaysandlimitedtorque(orcurrent)controlbandwidthareimportantandcannotbeneglected.Frommodelsincludingthesenon-idealpropertiesofthecontrolsystem,explicitexpressionsforstabilizationcontrollerstousewithISCaswellasfield-orientedcontrol(FOC)arederived.Thisisvaluableasstabilizationoftenisdesignedthroughcostlyandtime-consumingmanualtuning.Inthecontrollerdesign,thetrade-offbetweentighttorquecontrolandstabilityoftheDC-linkisalsoexplicitlyconsidered.Inthiswayreasonablestabilitymarginsareobtained,whileminimizingthenegativeeffectsontorquecontrol.Stabilityoftheclosed-loopdrivewiththeproposedstabilizationisvalidatedthroughrealistichardware-in-the-loopsimulationsusingrealcontrolHWandSW.Usingmodelsobtainedfromfrequencydomainsystemidentification,stabilityofthenon-linearclosed-loopdriveisverifiedbycombiningstabilityresultsforlinearsystemswiththesmallgaintheoremforthenon-linearmodelerrors.Thisthesisconsiderstheinputfilterdynamicsinconnectionwithtorquecontrolofaninductionmotor.Thekeyresultisamodel-basedframeworkforsimultaneoustreatmentofDC-linkstabilityandefficienttorquecontrol.AcknowledgementsThisworkistheresultofacollaborationbetweenBombardierTransportationinVästeråsandKTHinStockholm.Iwouldfirstofallliketoexpressmygratitudetothepeoplewhomadethisworkpossibleinthefirstplace.TheseincludemysupervisoratKTH,Prof.BoWahlbergandPeterOomandDr.KentÖhrnatBombardierTransportation.MytechnicalsupervisoratBombardierTransportationwasJohannGalic.Withouthisexperienceanddeepknowledgeofdrives,powerelectronicsandcontrol,thisworkwouldnothavebeencompleted.Thanksforsharingyourtimeandyourwisdom,Johann!IwouldalsoliketothankProf.StefanÖstlundforsupportregardinggeneralissuesrelatedtoinductionmotorcontrolandthepeopleintroducingmetothesubject,Dr.SteffenRichter,Dr.PeterKrafkaandMichaelRampe,whomIhavehadthepleasuretoworkwith.IwanttothankProf.AndersHelmerssonforvaluablehelpwithnumericallysolvingtheLMIsinChapter9andProf.EllingJacobsenforteachingmerobustmultivariablefeedbackcontrol.EvaSandbergwaskindtohelpmewiththelayoutinMicrosoftWordandKarinKarlsson-EklundguidedmethroughtheadministrativeroutinesatKTH.ThisworkwaspartlysupportedbyTheSwedishScienceFoundation,whichisgratefullyacknowledged.Finally,Iwouldliketothankmyfamilyforsupportandencouragement.Contents1Introduction.........................................................................11.1Background.....................................................................................21.2InductionMotorDrive....................................................................31.3TorqueControlofanInductionMotor............................................61.3.1Field-OrientedControl(FOC).............................................61.3.2DirectTorqueControl(DTC)..............................................71.4DC-LinkStability..........................................................................101.4.1ConstantPowerOperation.................................................101.4.2StabilizationwithPerfectTorqueControl.........................121.4.3ImprovedStabilizationStructure.......................................141.4.4ImprovedModelingforStabilizationSynthesis................161.4.5InputFilterOscillationswithDC-DCConverters.............181.5NotationandNomenclature..........................................................191.6OutlineandContributions.............................................................202VoltageSourceInverter....................................................252.1Three-PhaseVoltageSourceInverter...........................................252.2Modulation...................