过程控制复习资料

PRECESSCONTROLSYSTEM20105107DAN1PROCESSCONTROLSYSTEMREVIEWCHAPTER1INTRODUCTION1.TypicalControlledVariablesTemperature,Pressure,Flow,Level,Concentration,Physicalproperty2.TerminologyintheprocessTheControlledVariable(CV),theManipulatedVariable(MV)FactorscausingCVtodeviatefromtheirsetpointsiscalledtheDisturbanceor“LoadVariables3.TwoClassesofProcessControlRegulatorycontrol-disturbancechange,Servoingcontrol-setpointchange4.ControlEquipmentProcessEquipment5.Modeling1)TheoreticalModeling:Physical/chemicallaws(fundamental,global)Material/energybalancesHeat,mass,andmomentumtransferThermodynamics,chemicalkineticsPhysicalpropertyrelationships2)EmpiricalModeling(BlackBox)LargenumberofunknownparametersBeingobtainedquickly(e.g.,linearregression)ModelstructureissubjectiveDangeroustoextrapolatePRECESSCONTROLSYSTEM20105107DAN2CHAPTER3DYNAMICRESPONSE1.Analysisofthe1stOrderProcess1)Property1:yincreasesfrom0toanewsteadystateMK,thusself-regulating(Integratingprocess:Non-self-regulating)2)Property2:SteadystategainK=y/M,ThelargergainK,themoresensitiveistheoutputtothechangeintheinput3)Property3:Att=τ,theoutputisy=0.632MK4)Property4:Theshorterthespacetimeτ,thefasterreachesthenewsteadystate2.Analysisofthe2ndOrderProcess)(01222tbxyadtdyadtyda1)4variables3.ProcesseswithDeadTime1)PadéapproximationThe1ndorderPadéapproximationThe2ndorderPadéapproximation2)Twoplantshavedifferentintermediatevariablesbuthavethesameinput-outputbehavior!SteadystategaintransferfunctionPRECESSCONTROLSYSTEM20105107DAN3CHAPTER5ANALYSISOFSISOSYSTEM1.PIDControllers1)TheProportionalBand(PB)istheinverseoftheGain.InthesenseofproportionalbandPBThehigherPB,theslower(andmorestable)control.ThelowerPB,thefaster(andlessstable)control.2)KcThehighergain,thefaster(lessstable)control;Thelowergain,theslower(morestable)control.ThelargerKc,thefasteristhechangetoagivenerror;ToolargeKcwillmaketheprocessunstable3)Integralactionmakestheprocesssaturation,resetwindupA.Integraltermtakesonafinalnonzerovalue,thuspermittingestostayatzero,astimeprogressesB.theresetelementofthecontrollercontinuestoincrease(ordecrease)thecontrolleroutputC.evenwhenthechangeinoutputdoesnotcauseanychangeintheprocessmeasurement(controlledvariable).D.withnoresultingdecreaseinerror,theoutputwillcontinuetoincreaseuntilitreachesitslimit.4)Asmallchangeinerrormayproduceabigcontrolleroutputoccurringinchangingsetpoint(derivativekick),exhibitinginhigh-frequencynoise5)ThePropertiesofP,I,DControl:fromtimestandpointt=0t=tt=T(Tt)ProportionalModeP-ControlPersistentModeI-ControlPredictiveModeD-ControlHistoricalperiodCurrentTimeFutureTimePRECESSCONTROLSYSTEM20105107DAN42.Thestirred-tankheaterThetransferfunctionsforthesystemareGpfortheprocess(plant)GLfortheload(disturbance)GcforthecontrollerGmforthemeasuringdevice,withthesteadystategainKmGafortheactuator1）２）３）４）1.inletTi,and2.jackettemperatureTHPRECESSCONTROLSYSTEM20105107DAN5５）DerivingthesinglelooptransferfunctionAtthesummingpoint:Fortheprocess:SubstitutingEintoC,wehave:３．ConsiderationsofChoosingVariables１）ChoiceofcontrolledvariablesThosethataredictatedbytheproblemThosethatarenotself-regulatingThosethatmayexceedequipmentorprocessconstraintsThosethatmyinteractwithothervariable２）ChoiceofmanipulatedvariablesThosethathaveadirecteffectontheprocess,especiallytheoutputvariable.Thosethathavealargesteadystategain.(Goodsensitivity)Thosethathavenodeadtime(usuallynotsatisfied).Thosethathavenointeractionwithothercontrolloops.４．使用终值定理求解ess5.SelectionandActionofControllers--Air-to-OpenandFail-ClosedValve1)Ifhdropsbelowthesetpoint,controllerincreasesthesignaltoopenthevalvewith+Kv,thusair-to-openUnderthesystemfailurewherepowerislost,thevalveisclosed,thusfail-closedvalve2)ThecontrollerdesignalsohastwoscenariosaUsingthecontrollerwithpositivegain+Kc,orb.Usingthecontrollerwithnegativegain-Kc3)Scenario1whileKpisnegativeaIfusingacontrollerwithpositivegain+Kc,Wecanonlyuseanair-to-closevalve(-Kv)toreducingtheflow;bInthecaseofpoweroutage,thevalvewillstayopen,thusThefail-openvalvecandraintheentiretank(disaster)4)Scenario2whileKpisnegativeaIfusinganair-to-openvalve(Kv)attheoutletlocationWecanonlyusecontrollerwith-KctoreducingtheflowbWith-Kcastheproportionalgain,aliquidleveldropwillleadtoadecreaseincontrolleroutput,thusWehaveafail-closedvalve(desirable)PRECESSCONTROLSYSTEM20105107DAN6CHAPTER6DesignandTuningofSingle-LoopControlSystem1.TuningControllerswithEmpiricalRelations1)ApracticeofdesigningthecontrollersettingsMakinganopen(orclosed)loopexperimentFittingthesystemresponsetoamodel2)Calculatingthecontrollergainsusingthefittingcurve(empiricalmodel)Followingsomeempiricalrelations3)EmpiricaltuninggivesaquickstartingpointThoughitdoesnot’tdictatesystemdynamicspecificationsItisseldomoptimal,involvingfieldtuning4)WaysCohen-CoonRelationZiegler-NicholsRelation,ITAErelation,Ancon-Marlinrelation,Ziegler-Nicholsultimatemethod2.ControllersettingsBasedonPRC(processreactioncurve)1)Obtainingprocessreactioncurve(PRC)DisablingthecontrollerIntroducingastepchangetotheactuatorMeasuringtheopenloopstepresponse,resultinginPRC2)