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外文翻译--内嵌于可编程控制器的先进控制算法 英文文版.pdf

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外文翻译--内嵌于可编程控制器的先进控制算法 英文文版.pdf

ControlEngineeringPracticeembeddedVrancLjubljana,bNovaGoricaPolytechnic,NovaGorica,Sloveniaidentificationstepstoprovidereliableoperation.Thecontrollermonitorsandevaluatesthecontrolperformanceoftheclosedloopsystem.ThecontrollerwasimplementedonaprogrammablelogiccontrollerPLC.Theperformanceisillustratedonafieldtestinindustrialapplications,assummarisedbelowARTICLEINPRESSwww.elsevier.com/locate/conengpracC3Correspondingauthor.Tel.386147739941.Becauseofthediversityofreallifeproblems,asinglenonlinearcontrolmethodhasarelativelynarrow09670661/seefrontmatterr2005ElsevierLtd.Allrightsreserved.doi10.1016/j.conengprac.2005.05.006fax38614257009.Emailaddresssamo.gerksicijs.siS.Gerksˇicˇ.applicationforcontrolofpressureonahydraulicvalve.r2005ElsevierLtd.Allrightsreserved.KeywordsControlengineeringFuzzymodellingIndustrialcontrolModelbasedcontrolNonlinearcontrolProgrammablelogiccontrollersSelftuningregulators1.IntroductionModerncontroltheoryoffersmanycontrolmethodstoachievemoreefficientcontrolofnonlinearprocessesthanprovidedbyconventionallinearmethods,takingadvantageofmoreaccurateprocessmodelsBequette,1991HensonSeborg,1997MurraySmithJohansen,1997.SurveysTakatsu,Itoh,Araki,1998Seborg,1999indicatethatwhilethereisaconsiderableandgrowingmarketforadvancedcontrollers,relativelyfewvendorsofferturnkeyproducts.Excellentresultsofadvancedcontrolconcepts,basedonfuzzyparameterschedulingTan,Hang,Chai,1997Babusˇka,Oosterhoff,Oudshoorn,Bruijn,2002,multiplemodelcontrolDoughertyCooper,2003Gundala,Hoo,Piovoso,2000,andadaptivecontrolHensonSeborg,1994Ha¨gglundA˚strom,2000,havebeenreportedintheliterature.However,thereareseveralrestrictionsforapplyingthesemethodsdINEAd.o.o.,Ljubljana,SloveniaeComputerTechnologyInstitute,Athens,GreecefUniversityofChemicalTechnologyandMetallurgySofia,Sofia,BulgariaReceived23April2004accepted15May2005AbstractThispaperpresentsaninnovativeselftuningnonlinearcontrollerASPECTadvancedcontrolalgorithmsforprogrammablelogiccontrollers.Itisintendedforthecontrolofhighlynonlinearprocesseswhosepropertieschangeradicallyoveritsrangeofoperation,andincludesthreeadvancedcontrolalgorithms.Itisdesignedusingtheconceptsofagentbasedsystems,appliedwiththeaimofautomatingsomeoftheconfigurationtasks.Theprocessisrepresentedbyasetofloworderlocallinearmodelswhoseparametersareidentifiedusinganonlinelearningprocedure.ThisprocedurecombinesmodelidentificationwithpreandpostcUniversityofLjubljana,FacultyofElectricalEngineering,Ljubljana,SloveniaAdvancedcontrolalgorithmslogiccontrollerSamoGerksˇicˇa,C3,GregorDolanca,DamirSasˇoBlazˇicˇc,IgorSˇkrjancc,ZoranMarinsRobertKinge,MinchoHadjiskiaJozˇefStefanInstitute,inaprogrammableˇic´a,JusˇKocijana,b,StankoStrmcˇnika,ˇekd,MihaBozˇicˇekd,AnnaStathakie,f,KostaBoshnakovfSlovenia–friendmaticindustfromling,procedcontrollermonitorstheresultingcontrolperformanceARTICLEINPRESSanonlinearprocessmodel.Themodelisobtainedoperatingprocesssignalsbyexperimentalmodelusinganovelonlinelearningprocedure.ThisThefromforimplementationonPLCoropencontrollerrialhardwareplatforms.controllerparametersareautomaticallytunedfeatuadaptedssioningofthecontrollerissimplifiedbyautoexperimentationandtuning.AdistinguishingreofthecontrolleristhatthealgorithmsaremetecommiTheASPECTcontrollerisanefficientanduserlyengineeringtoolforimplementationofpararschedulingcontrolintheprocessindustry.Theused,thesensorreadings,specifichardwareplatformsareetc.isdemandedtofieldofapplication.Therefore,moreflexiblemethodsoratoolboxofmethodsarerequiredinindustry.2.Newmethodsareusuallynotavailableinareadytouseindustrialform.Customdesignrequiresconsiderableeffort,timeandmoney.3.Thehardwarerequirementsarerelativelyhigh,duetothecomplexityofimplementationandcomputationaldemands.4.ThecomplexityoftuningBabusˇkaetal.,2002andmaintenancemakesthemethodsunattractivetononspecialisedengineers.5.Thereliabilityofnonlinearmodellingisofteninquestion.6.ManynonlinearprocessescanbecontrolledusingthewellknownandindustriallyprovenPIDcontroller.Aconsiderabledirectperformanceincreasefinancialgainisdemandedwhenreplacingaconventionalcontrolsystemwithanadvancedone.Themaintenancecostsofaninadequateconventionalcontrolsolutionmaybelessobvious.TheaimofthisworkistodesignanadvancedcontrollerthataddressessomeoftheaforementionedproblemsbyusingtheconceptsofagentbasedsystemsABSWooldridgeJennings,1995.Themainpurposeistosimplifycontrollerconfigurationbypartialautomationofthecommissioningprocedure,whichistypicallyperformedbythecontrolengineer.ABSsolvedifficultproblemsbyassigningtaskstonetworkedsoftwareagents.Thesoftwareagentsarecharacterisedbypropertiessuchasautonomyoperationwithoutdirectinterventionofhumans,socialabilityinteractionwithotheragents,reactivityperceptionandresponsetotheenvironment,proactivenessgoaldirectedbehaviour,takingtheinitiative,etc.ThisworkdoesnotaddressissuesofABStheory,butrathertheapplicationofthebasicconceptsofABStothefieldofprocesssystemsengineering.Inthiscontext,anumberoflimitshavetobeconsidered.Forexampleinitiativeisrestricted,ahighdegreeofreliabilityandpredictability,insightintotheproblemdomainislimitedS.Gerksˇicˇetal./ControlEngineerin2ureisbasedonmodelidentificationusingtheandreactstodetectedirregularities.ThecontrollercomprisestheruntimemoduleRTMandtheconfigurationtoolCT.TheRTMrunsonaPLC,performingallthemainfunctionalityofrealtimecontrol,onlinelearningandcontrolperformancemonitoring.TheCT,usedonapersonalcomputerPCduringtheinitialconfigurationphase,simplifiestheconfigurationprocedurebyprovidingguidanceanddefaultparametervalues.TheoutlineofthepaperisasfollowsSection2presentsanoverviewoftheRTMstructureanddescribesitsmostimportantmodulesSection3givesabriefdescriptionoftheCTandfinally,Section4describestheapplicationofthecontrollertoapilotplantwhereitisusedforcontrolofthepressuredifferenceonahydraulicvalveinavalvetestapparatus.2.RunTimeModuleTheRTMoftheASPECTcontrollercomprisesasetofmodules,linkedintheformofamultiagentsystem.Fig.1showsanoverviewoftheRTManditsmainmodulesthesignalpreprocessingagentSPA,theonlinelearningagentOLA,themodelinformationagentMIA,thecontrolalgorithmagentCAA,thecontrolperformancemonitorCPM,andtheoperationsupervisorOS.2.1.MultifacetedmodelMFMTheASPECTcontrollerisbasedonthemultifacetedmodelconceptproposedbyStephanopoulus,Henning,andLeone1990andincorporatesseveralmodelformsrequiredbytheCAAandtheOLA.Specifically,theMFMincludesasetoflocalfirstandsecondorderlocallearningapproachMurraySmithJohansen,1997,p.188.Themeasurementdataareprocessedbatchwise.Additionalstepsareperformedbeforeandafteridentificationinordertoimprovethereliabilityofmodelling,comparedtoadaptivemethodsthatuserecursiveidentificationcontinuouslyHa¨gglundA˚strom,2000.Thenonlinearmodelcomprisesasetoflocalloworderlinearmodels,eachofwhichisvalidoveraspecifiedoperatingregion.Theactivelocalmodelsisselectedusingaconfiguredschedulingvariable.Thecontrollerisspecificallydesignedforsingleinput,singleoutputprocessesthatmayincludeameasureddisturbanceusedforfeedforward.Additionally,theapplicationrangeofthecontrollerdependsontheselectedcontrolalgorithm.Amodularstructureofthecontrollerpermitsuseofarangeofcontrolalgorithmsthataremostsuitablefordifferentprocesses.ThegPractice–discretetimelinearmodelswithtimedelayandoffset,ARTICLEINPRESSS.Gerksˇicˇetal./ControlEngineerinwhicharespecifiedbyagivenschedulingvariablesk.Themodelequationoffirstorderlocalmodelsisyðkþ1Þ¼C0a1jyðkÞþb1juðkC0dujÞþc1jvðkC0dvjÞþrj,1whilethemodelequationofsecondordermodelsisyðkþ1Þ¼C0a1jyðkÞC0a2jyðkC01Þþb1juðkC0dujÞþb2juðkC01C0dujÞþc1jvðkC0dvjÞþc2jvðkC01C0dvjÞþrj,ð2Þwherekisthediscretetimeindex,jisthenumberofthelocalmodel,ykistheprocessoutputsignal,ukistheprocessinputsignal,vkistheoptionalmeasureddisturbancesignalMD,duisthedelayinthemodelbranchfromutoy,dvisthedelayinthemodelbranchfromvtoy,andai,j,bi,j,ci,jandrjaretheparametersofthejthlocalmodel.ThesetoflocalmodelscanbeinterpretedasaTakagi–Sugenofuzzymodel,whichinthecaseofasecondordermodelcanbeexpressedintheFig.1.RuntimemodulegPractice–3followingformyðkþ1Þ¼C0Xmj¼1bjðkÞa1jyðkÞC0Xmj¼1bjðkÞa2jyðkC01ÞþXmj¼1bjðkÞb1juðkC0dujÞþXmj¼1bjðkÞb2juðkC01C0dujÞþXmj¼1bjðkÞc1jnðkC0dnjÞþXmj¼1bjðkÞc2jnðkC01C0dnjÞþXmj¼1bjðkÞrj,ð3Þwherebjkisthevalueofthemembershipfunctionofthejthlocalmodelatthecurrentvalueoftheschedulingvariablesk.Normalisedtriangularmembershipfunctionsareused,asillustratedinFig.2.overview.ARTICLEINPRESSTheschedulingvariableskiscalculatedusingcoefficientskr,ky,ku,andkv,usingtheweightedsumsðkÞ¼krrðkÞþkyyðkÞþkuuðkC01ÞþkvvðkÞ.4Thecoefficientsareconfiguredbytheengineeraccordingtothenatureoftheprocessnonlinearity.2.2.OnlineLearningAgentOLATheOLAscansthebufferofrecentrealtimesignals,preparedbytheSPA,andestimatestheparametersofthelocalmodelsthatareexcitedbythesignals.ThemostrecentlyderivedparametersaresubmittedtotheMIAonlywhentheypasstheverificationtestandareprovedtobebetterthantheexistingset.TheOLAisinvokedupondemandfromtheOSorautonomously,whenanintervaloftheprocesssignalswithsufficientexcitationisavailableforprocessing.Itprocessesthesignalsbatchwiseandusingthelocallearningapproach.Anadvantageofthebatchwiseconceptisthatthedecisiononwhethertoadaptthemodelisnotperformedinrealtimebutfollowingadelaythatallowsforinspectionoftheidentificationresultbeforeitisapplied.Thus,bettermeansforcontroloverdataselectionisprovided.Aproblemofdistributionofthecomputationtimerequiredforidentificationappearswithbatchwiseprocessingofdataopposedtotheonlinerecursiveprocessingthatistypicallyusedinadaptivecontrollers.Thisproblemisresolvedusingamultitaskingoperationsystem.SincetheOLAtypicallyrequiresconsiderablyFig.2.FuzzymembershipfunctionsoflocalmodelsintheMFM.S.Gerksˇicˇetal./ControlEngineerin4morecomputationthantherealtimecontrolalgorithm,itrunsinthebackgroundasalowprioritytask.Thefollowingprocedure,illustratedinFig.3,isexecutedwhentheOLAisinvoked.2.2.1.CopysignalbufferThebufferoftherealtimesignalsismaintainedbytheSPA.WhentheOLAisinvoked,therelevantsectionofthebufferiscopiedforfurtherprocessing.2.2.2.ExcitationcheckAquickexcitationcheckisperformedatthestart,sothatprocessingofthesignalsisperformedonlywhentheycontainexcitation.Ifthestandarddeviationsofthesignalsrk,yk,uk,andvkintheactivebufferarebelowtheirthresholds,theexecutioniscancelled.2.2.3.CopyactiveMFMfromMIATheonlinelearningprocedurealwayscomparesthenewlyidentifiedlocalmodelswiththeprevioussetofparameters.Therefore,theactiveMFMiscopiedfromtheMIAwhereitisstored.AdefaultsetofmodelparametersisusedforthelocalmodelsthathavenotyetbeenidentifiedseeSection2.3.2.2.4.SelectlocalmodelsAlocalmodelisselectedifthesumofitsmembershipfunctionsbjkovertheactivebuffernormalisedbytheactivebufferlengthexceedsagiventhreshold.Onlytheselectedlocalmodelsareincludedinfurtherprocessing.2.2.5.IdentificationThelocalmodelparametersareidentifiedusingthefuzzyinstrumentalvariablesFIVidentificationmethoddevelopedbyBlazˇicˇetal.2003.ItisanextensionofthelinearinstrumentalvariablesidentificationprocedureLjung,1987forthespecifiedMFM,basedonthelocallearningapproachMurraySmithJohansen,1997.Thelocallearningapproachisbasedontheassumptionthattheparametersofalllocalmodelswillnotbeestimatedinasingleregressionoperation.Comparedtotheglobalapproachitislesspronetotheproblemsofillconditioningandlocalminima.Thismethodiswellsuitedtotheneedsofindustrialoperationintuitiveness,gradualbuildingofthenonlinearmodel,modestcomputationaldemands.Itenablesinventoryofthelocalmodelsthatarenotestimatedproperlyduetoinsufficientexcitation.Itisefficientandreliableinearlyconfigurationstages,whenalllocalmodelshavenotbeenestimatedyet.Ontheotherhand,theconvergenceinthevicinityoftheoptimumisslow.Therefore,itislikelytoyieldaworsemodelfitthanmethodsemployingnonlinearoptimisation.Thefollowingbrieflydescribestheprocedure.Modelidentificationisperformedforeachselectedlocalmodeldenotedbytheindexjseparately.TheinitialestimatedparametervectorhjMIAiscopiedfromtheactiveMFM,andthecovariancematrixPj,MIAisinitialisedto105Iidentitymatrix.TheFLSfuzzyleastsquaresestimates,hjFLSandPj,FLS,areobtainedusingweightedleastsquaresidentification,withbjkusedforweighting.Thecalculationisperformedrecursivelytoavoidmatrixinversion.TheFIVfuzzyinstrumentalvariablesestimates,hjFIVandPj,FIV,arecalculatedusingweightedinstrumentalvariablesidentification.Inordertopreventresultdegradationbynoise,agPractice–deadzoneisusedineachstepofFIVandFLSrecursive

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