您好,欢迎访问三七文档
Ch3Feedbackcontrolsystemcharacteristics•Open-andclosed-loopcontrolsystems•SensitivitytoParametervariations•Transientresponseofcontrolsystem•DisturbanceinfeedbackcontrolsystemMaincontent:continue•Steady-stateerror•Thecostoffeedback•ExamplesandsimulationMaincontent:3.1Open-loopandclosed-loopcontrolsystems•Reviewtheconceptsandstructure•RefertoP174-175Therolesoffeedback•Reduceerror(eliminatingtheerror)•ReducesensitivityorEnhancerobustness•Disturbancerejectionorelimination•Improvedynamicperformanceoradjustthetransientresponse(suchasreducetimeconstant)Benefits:3.2SensitivityofsystemtoparametervariationsSystemaretime-varyinginitsnaturebecauseofinevitableuncertaintiessuchaschangingenvironment,aging,andotherfactorsthataffectacontrolprocess.Alltheseuncertaintiesinopen-loopsystemwillresultininaccurateoutputorlowperformance.However,aclosed-loopsystemcanovercomethisdisadvantage.Aprimaryadvantageofaclosed-loopfeedbackcontrolsystemisitsabilitytoreducethesystem’ssensitivitytoparametervariation.SensitivityanalysisRobustcontrolContinueEffectofparametervariationsIfprocessischangeas)(sG)()(sGsG•Open-loopsystem)()()(sRsGsY•Closed-loopsystem)()1()()()1)(1()()(2sRGHsGsRGHGHGHsGsYcontinueInthelimit,forsmallincrementalchanges,lastformulaisInGInTsGsGsTsTS)(/)()(/)(Sensitivitycomparison•Open-loopsystem•Closed-loopsystem1TGS)()(11sHsGSTGSensitivitytoparametersIfsystemTFis),(),(),(sDsNsTSystemsensitivitytoisDNTSSInInDInInNInInTSExampleofsensitivity•Feedbackamplifier•Goal:Reducethesensitivitytoparametersvariation,thatisenhancetherobustnesstochangeinamplifiergain.Referto178-1793.3Transientresponseofsystem•Transientresponseistheresponseofasystemasafunctionoftime.Itisoneofthemostimportantcharacteristicsofcontrolsystem.•Iftransientresponseisnotsatisfying,whatshallwedo?Controloftransientresponse(Takespeedcontrolsystemasexample)•Cascadecontroller•FeedbackcontrollerRefertoP180(Figure4.6andFigure4.7)RefertoP181(Figure4.8)3.4Disturbanceinafeedbackcontrolsystem•Disturbancesignalisanunwantedextraneousinputsignalthataffectsthesystem’soutputsignal,suchasnoiseforamplifier,windgustsforradarantennas,etc.•Feedbackcontrolcancompletelyorpartiallyeliminatetheeffectofdisturbancesignal.Exampleofsteelrollingmill•RefertoP183-187•Loadchangesordisturbances+Noise•Feedbackcanalleviatetheeffectsofdisturbancesandnoisesignaloccurringwithinthefeedbackloop.•Ifsystemexistsnoiseattheinputpoint,wecandesignalow-passfiltertoimproveSNR(signal-noiseratio)SystemsensitivitySystemsensitivityisdefinedastheratioofthepercentagechangeinthesystemtransferfunctiontothepercentagechangeoftheprocesstransferfunction.Itisdefinedas)(/)()(/)(sGsGsTsTS3.5Steady-stateerror•Steady-stateerroristheerrorafterthetransientresponsehasdecayed,leavingonlythecontinuousresponse.•Feedbackcanreducethesteady-stateerrorofcontrolsystemHowtodefinetheerror?•Frominputpoint:•Fromoutputpoint:Ea(s)=R(s)-H(s)Y(s)E(s)=R(s)-Y(s)OnlyforunitfeedbackH(s)=1,WehaveEa(s)=E(s)Comparisonoferror)())(1()()()(sRsGsYsRsEo1)(,)()(11)(sHforsRsGsEo•Open-loopsystem•Closed-loopsystemcontinue•Open-loopsystemunderunitstepinput•Closed-loopsystemunderunitstepinput)0(11))(1(lim)(lim)(00GssGsssEesoso)0(111))(11(lim)(lim)(00GssGsssEescscExampleillustration•RefertoP189-190Anexampleoffirst-ordersystem3.6Thecostoffeedback•Increaseofcomplexity•Lossofgain•InstabilityAnunrealisticdream•WhynotsimplysetG(s)=Y(s)/R(s)=1?•Transferfunctionrepresentthephysicalsystemorprocess,ThereforeG(s)=1isunrealizable.3.7Designexamples•Englishchannelboringmachines•MarsrovervehiclePDcontroller,andhowtoselectK?Tocomparethesensitivityandsteady-stateerrorbetweenopen-loopandclosed-loopsystem3.8SimulationusingMATLAB•RefertoP196-202•Self-learningafterclassSummary•Decreasethesensitivitytoparametervariation•Improvetransientordynamicperformance•Enhancetherobustness•Reducethesteady-stateerrorThefundamentalreasonsforusingfeedbackareasfollows:RefertoP205-207Assignment•E4.1•E4.3•E4.4•E4.6•E4.8•P4.2,P4.5,P4.7
本文标题:open-and closed-loop control systems sensitivity t
链接地址:https://www.777doc.com/doc-3458826 .html