Основен преглед
PID контролер(ProportionIntegrationDifferentiation.ProportionIntegrationDifferentiation.Proportion-Integral-DerivativeController), състоящ се от пропорционална единицаP, интегрална единицаIи производна единицаDcomposition.Чрез настройката наKp,KiиKdтри параметъра.PID контролерите са подходящи главно за системи, чиято основна линейност и динамични характеристики не се променят с времето.
PIDcontrollerisacommonfeedbackloopcomponentinindustrialcontrolapplications.Thiscontrollercomparesthecollecteddatawithareferencevalue,andthenusesthisdifferencetocalculateanewinputvalue.Thepurposeofthisnewinputvalueistoallowthesystemdatatoreachormaintainthereferencevalue.Differentfromothersimplecontrolcalculations,PIDcontrollercanadjusttheinputvalueaccordingtohistoricaldataandtheoccurrencerateofdifference,whichcanmakethesystemmoreaccurateandmorestable.ItcanbeprovedbymathematicalmethodsthataPIDfeedbackloopcankeepthesystemstablewhenothercontrolmethodsleadtosystemstabilityerrorsorprocessrepetitions.
Обратна връзка
Контролна верига се състои от три части:
Themeasurementresultsobtainedbythesystem’ssensors,thecontrollermakesthedecisionandreactsthroughanoutputdevicetocontrolThedeviceobtainsthemeasurementresultfromthesensor,andthensubtractsthemeasurementresultfromthedemandresulttogettheerror.Thenusetheerrortocalculateacorrectionvaluetothesystemastheinputresult,sothatthesystemcaneliminatetheerrorfromitsoutputresult.
InaPIDloop,therearethreealgorithmsforthiscorrectionvalue,eliminatingerrors,averagingpasterrors,andpredictingfutureerrorsthroughchangesinerrors.
Forexample,ifawatertankisprovidingwaterforaplant,thewaterinthistankneedstobekeptatacertainheight.Asensorwillbeusedtochecktheheightofthewaterinthetank,sothatthemeasurementresultisobtained.Thecontrollerwillhaveafixeduserinputvaluetoindicatetherequiredwatersurfaceheightofthewatertank,assumingthisvalueistomaintain65%ofthewatervolume.Theoutputdeviceofthecontrollerwillbeconnectedtoamotor-controlledwatervalve.Openingthevalvewillfillthewatertank,andclosingthevalvewillreducetheamountofwaterinthewatertank.Thecontrolsignalofthisvalveisthevariablewecontrol,anditisalsotheinputofthissystemtokeepthewatertankfixed.
PIDcontrollercanbeusedtocontrolanyvariablethatcanbemeasuredandcontrolled.Forexample,itcanbeusedtocontroltemperature,pressure,flow,chemicalcomposition,speedandsoon.Thecruisecontrolfunctiononacarisanexample.
SomecontrolsystemsconnectseveralPIDcontrollersinseries,orchainthemintoanetwork.Inthiscase,amaincontrollermayoutputresultsforothercontrols.Acommonexampleisthecontrolofmotors.Wewilloftenneedthemotortohaveacontrolledspeedandstopatacertainposition.Inthisway,asub-controllermanagesthespeed,butthespeedofthissub-controllerismanagedbythemaincontrollerthatcontrolsthepositionofthemotor.
Combinationandseriescontrolareverycommoninchemicalprocesscontrolsystems.
Theory
PIDisnamedafteritsthreecorrectionalgorithms.Allthreealgorithmsuseadditiontoadjustthecontrolledvalue.Infact,mostoftheseadditionoperationsbecomesubtractionoperationsbecausetheaddendisalwaysnegative.Thesethreealgorithmsare:
Пропорция-За контролиране на тока, стойността на грешката се умножава по отрицателна константаP(пропорция) и след това предварително определенаДобавя стойноститена.Pе вярно само когато изходът на контролера е пропорционален на грешката на системата.Промяната на изхода на контролера е пропорционална на отклонението на входния контролер .Например обхватът на скалата на контролера за електрически нагревател е 10° C, а предварително определената му стойност е 20°C. Той ще изведе 100% при 10°C, 50% при 15°C и 10% при 19°C. Имайте предвид, че когато грешката е 0, изходът на контролера също е 0.
Integration-Tocontrolthepast,theerrorvalueisthesumoftheerrorsinthepastperiodoftime,andthenmultipliedbyanegativeconstantI,andthencomparedwiththepredeterminedvalueadd.IFindtheaverageerrorbetweentheoutputresultofthesystemandthepredeterminedvaluefromtheaverageerrorvalueinthepast.Asimpleproportionalsystemwilloscillateandchangebackandfortharoundapredeterminedvaluebecausethesystemcannoteliminateredundantcorrections.Byaddinganegativeaverageerrorratiovalue,theaveragesystematicerrorvaluewillalwaysdecrease.Therefore,intheend,thePIDloopsystemwillbesetatapredeterminedvalue.
Производна-За да контролирате бъдещето, изчислете първата производна на грешката, умножете я по отрицателната константаD и накрая добавете към предварително определената стойност. Контролът на тази производна ще реагира на промените в системата. Колкото по-голям е резултатът на производната, толкова по-бързо системата за управление ще реагира на изходния резултат. >параметърът също е причина, поради която PID се нарича предсказуем контролер.D параметърът е много полезен за намаляване на краткосрочните промени на контролера. Някои бавни системи на практика може да не се нуждаят отDпараметъра. С по-професионална гледна точка, PID контролерът може да се нарече филтър в системата на честотния домейн. Това е полезно, когато се изчислява дали в крайна сметка ще се постигне стабилен резултат. Ако стойността не е избрана действа правилно, въведената стойност на системата за управление ще се колебае многократно, което може да доведе до това системата никога да не достигне предварително зададената стойност.
Закон за управление
Въпреки че различните типове контролери имат различни структури и принципи, има само три основни закона за управление: пропорционално (P) управление, интегрално (I) управление и производно (D) управление. Тези правила за управление могат да се използват самостоятелно, но се използват в комбинация в повече случаи. управление, пропорционално-интегрално (PI) управление, пропорционално -интегрално-производно (PID) управление и др.
Пропорционално (P) управление
Singleproportionalcontrolisalsocalled"differencecontrol",theoutputchangeisproportionaltothedeviationoftheinputcontroller,Thegreaterthedeviation,thegreatertheoutput.Inpracticalapplications,thedegreeofproportionalityshouldbedeterminedaccordingtothespecificsituation.Toolargeaproportionality,tooweakcontroleffect,isnotconducivetothesystemtoovercomedisturbances,themarginistoolarge,thecontrolqualityispoor,andthereisnocontroleffect;theproportionalityistoosmall,Thecontroleffectistoostrong,itiseasytocausethestabilityofthesystemtodeteriorateandcauseoscillation.
Forthecontrolledobjectwithsensitiveresponseandstrongamplificationability,inordertoimprovethestabilityofthesystem,theproportionalityshouldbeslightlylarger;forthecontrolledobjectwithslowresponseandweakamplificationability,theproportionalThedegreecanbeselectedtobesmallertoimprovethesensitivityoftheentiresystemandtoreducetheresidualsaccordingly.
Pureproportionalcontrolissuitableforoccasionswherethedisturbanceissmall,thehysteresisissmall,theloadchangeissmall,therequirementsarenothigh,andacertainmarginisallowed.Theuseofproportionalcontrollawinindustrialproductionismorecommon.
Пропорционалноинтегрално (PI) управление
Proportionalcontrollawisthemostbasicandmostcommonlyusedoneofthebasiccontrollaws.ItsgreatestadvantageisControlistimelyandrapid.Aslongasthereisadeviation,thecontrollerimmediatelytakescontrol.However,thedisadvantageofnotbeingabletofinallyeliminatetheresiduallimitsitsusealone.Thewaytoovercometheresidualistoaddintegralcontrolonthebasisofproportionalcontrol.
Theoutputoftheintegralcontrollerisproportionaltotheintegraloftheinputdeviationovertime.The"points"heremeans"accumulation".Theoutputoftheintegralcontrollerisnotonlyrelatedtothemagnitudeoftheinputdeviation,butalsorelatedtothetimethedeviationexists.Aslongasthedeviationexists,theoutputwillcontinuetoaccumulate(theoutputvalueisgettinglargerorsmaller),andtheaccumulationwillstopuntilthedeviationiszero.Therefore,integralcontrolcaneliminateresiduals.Theintegralcontrollawisalsocalledthenon-differencecontrollaw.
Thesizeoftheintegraltimecharacterizesthestrengthofintegralcontrol.Thesmallertheintegraltime,thestrongerthecontroleffect;onthecontrary,theweakerthecontroleffect.
Althoughintegralcontrolcaneliminatetheresidualerror,ithasthedisadvantageofnottimelycontrol.Becausetheaccumulationofintegraloutputisgradual,thecontroleffectitproducesalwayslagsbehindthechangeofthedeviation,andtheinfluenceofinterferencecannotbeovercomeintimeandeffectively,anditisdifficulttostabilizethecontrolsystem.Therefore,inpractice,integralcontrolisgenerallynotusedalone,butcombinedwithproportionalcontroltoformproportionalintegralcontrol.Inthisway,theadvantagesofthetwoareusedtomakeupforeachother,whichnotonlyhastherapidandtimelyeffectofproportionalcontrol,butalsohastheabilityofintegralcontroltoeliminatetheresidualerror.Therefore,proportionalintegralcontrolcanachieveamoreidealprocesscontrol.
Proportionalintegralcontrolleristhemostwidelyusedcontroller,whichismostlyusedinthecontrolsystemofliquidlevel,pressure,flow,etc.inindustrialproduction.Sincetheintroductionofintegralactioncaneliminatetheresidualerror,makeupfortheshortcomingsofpureproportionalcontrol,andobtainbettercontrolquality.Buttheintroductionofintegralactionwillmakethestabilityofthesystemworse.Forcontrolsystemswithlargeinertialag,trytoavoidusingthem.
Пропорционално производно (PD) управление
Proportionalintegralcontrolisnotidealforthecontrolledobjectwithtimelag.Theso-called"timelag"refersto:whenthecontrolledobjectisdisturbed,thecontrolledvariabledoesnotchangeimmediately,butthereisatimedelay,suchasacapacitylag,whentheproportionalintegralcontrolappearssluggishanduntimely.Forthisreason,peopleimagined:Canthecorrespondingcontrolactionbemadeaccordingtothechangingtrendofthedeviation?Justlikeexperiencedoperators,theycanchangethevalveopeningaccordingtothemagnitudeofthedeviation(proportionaleffect),andcanpredictthesituationthatwilloccuraccordingtothespeedofthedeviationchange,andcarryoutexcessivecontrolinadvanceto"preventproblemsbeforetheyoccur.".Thisisthedifferentialcontrollawwith"advanced"controlfunction.Theoutputofthederivativecontrollerdependsonthespeedatwhichtheinputdeviationchanges.
Thedifferentialoutputisonlyrelatedtothechangespeedofthedeviation,andhasnothingtodowiththesizeofthedeviationandwhetherthedeviationexistsornot.Ifthedeviationisafixedvalue,nomatterhowlarge,aslongasitdoesnotchange,theoutputchangemustbezero,andthecontrollerhasnocontroleffect.Thelongerthederivativetime,thelongerthederivativeoutputismaintained,sothestrongerthederivativeaction;otherwise,theweaker.Whenthederivativetimeis0,thereisnoderivativecontroleffect.Inthesameway,theselectionofthedifferentialtimealsoneedstobedeterminedaccordingtotheactualsituation.
Thecharacteristicsofthedifferentialcontrolfunctionare:rapidaction,withadvancedadjustmentfunction,whichcaneffectivelyimprovethecontrolqualityofthecontrolledobjectwithalargetimelag;butitcannoteliminatetheresidual,especiallyfortheconstantdeviationinputThereisnocontroleffectatall.Therefore,thedifferentialcontrollawcannotbeusedalone.
Thecombinationofproportionalanddifferentialactionisfasterthanpureproportionalaction.Especiallyforobjectswithlargecapacitylag,theamplitudeofdynamicdeviationcanbereduced,controltimecanbesaved,andcontrolqualitycanbesignificantlyimproved.
PID контрол
Themostidealcontrolistheproportional-integral-derivativecontrollaw.Itcombinestheadvantagesofthethree:boththeproportionalactionistimelyandrapid,theintegralactioncaneliminatetheresidualerror,andthedifferentialactionhastheadvancedcontrolfunction.
Whenthedeviationstepoccurs,thederivativewillactimmediatelytosuppressthisleapofdeviation;theratioalsoplaysaroleineliminatingthedeviation,sothatthedeviationrangeisreduced,becausetheproportionaleffectislastingandeffective.Themaineffectofthecontrollaw,sothatthesystemcanbemorestable;andtheintegraleffectgraduallyovercomestheresidualerror.Aslongasthecontrolparametersofthethreefunctionsareselectedproperly,theadvantagesofthethreecontrollawscanbefullyutilizedandamoreidealcontroleffectcanbeobtained.
Метод за отстраняване на грешки
Коригиране на пропорционалния коефициент
Обхватът на регулиране на пропорционалния коефициентP обикновено е 0,1--100.
Ifthegainvalueis0.1,thePIDregulatoroutputchangestoone-tenthofthedeviationvalue.Ifthegainvalueis100,theoutputofthePIDregulatorchangestoonehundredtimesthedeviationvalue.
Itcanbeseenthatthelargerthevalue,thegreaterthegaineffectproducedbytheratio.Intheinitialadjustment,chooseasmallervalue,andthenslowlyincreaseituntilthesystemfluctuationissmallenough,andthenadjusttheintegralordifferentialcoefficient.AtoolargePvaluewillcausethesystemtobeunstableandcontinuetooscillate;atoosmallPvaluewillmakethesystemunresponsive.Theappropriatevalueshouldenablethesystemtohavesufficientsensitivitybutnottoosensitive.Thedelayforacertainperiodoftimeshouldbeadjustedbytheintegrationtime.
Adjustmentoftheintegralcoefficient
Thedefinitionoftheintegraltimeconstantisthetimethatthedeviationcausestheoutputtoincrease.Iftheintegrationtimeissetto1second,thetimerequiredfora100%outputchangeis1second.Intheinitialadjustment,settheintegrationtimelonger,andthenslowlyadjustituntilthesystemisstable.
Adjustmentofthedifferentialcoefficient
Thedifferentialvalueistherateofchangeofthedeviationvalue.Forexample,iftheinputdeviationvaluechangeslinearly,aconstantadjustmentamountissuperimposedontheoutputsideoftheregulator.Mostcontrolsystemsdonotneedtoadjustthederivativetime.Becauseonlysystemswithtimelagneedtoaddthisparameter.Ifsuperfluousandaddingthisparameter,thecontrolofthesystemwillbeaffected.Iftheidealcontrolrequirementisstillnotreceivedthroughtheadjustmentoftheproportionalandintegralparameters,thederivativetimecanbeadjusted.Intheinitialadjustment,setthiscoefficienttoasmallvalue,andthenslowlyincreaseituntilthesystemisstable.
Parametertuning
PIDcontrollerparametertuningisthecorecontentofcontrolsystemdesign.Itdeterminestheproportionalcoefficient,integraltimeandderivativetimeofthePIDcontrolleraccordingtothecharacteristicsofthecontrolledprocess.TherearemanymethodsforPIDcontrollerparametertuning,whichcanbesummarizedintotwocategories:Oneisthetheoreticalcalculationtuningmethod.Itismainlybasedonthemathematicalmodelofthesystemtodeterminethecontrollerparametersthroughtheoreticalcalculations.Thecalculateddataobtainedbythismethodmaynotbedirectlyusable,andmustbeadjustedandmodifiedthroughactualengineering.Thesecondistheengineeringtuningmethod,whichmainlyreliesonengineeringexperienceandiscarriedoutdirectlyinthetestofthecontrolsystem,andthemethodissimpleandeasytomaster,andiswidelyusedinengineeringpractice.TheengineeringtuningmethodsofPIDcontrollerparametersmainlyincludecriticalproportionmethod,responsecurvemethodandattenuationmethod.Thethreemethodshavetheirowncharacteristics.Thecommonpointisthattheypassthetest,andthenadjustthecontrollerparametersaccordingtotheengineeringexperienceformula.However,nomatterwhichmethodisused,thecontrollerparametersobtainedneedtobeadjustedandperfectedinactualoperation.Thecriticalratiomethodisgenerallyusednow.ThestepsfortuningPIDcontrollerparametersusingthismethodareasfollows:(1)First,pre-selectashortenoughsamplingperiodforthesystemtowork;(2)Onlyaddproportionalcontrollinksuntilthesystemhascriticaloscillationsinitsstepresponsetotheinput.Writedowntheproportionalamplificationfactorandcriticaloscillationperiodatthistime;(3)Underacertaindegreeofcontrol,theparametersofthePIDcontrollercanbecalculatedbyformulas.
Адаптивно управление
Firstofall, разберете какво е адаптивно управление
Intheproductionprocess,inordertoimproveproductquality,increaseoutput,saverawmaterials,productionmanagementandTheproductionprocessisalwaysinoptimalworkingcondition.Therefore,anoptimalcontrolmethodisproduced,whichiscalledadaptivecontrol.Inthiskindofcontrol,thesystemisrequiredtobeabletoautomaticallyadjustthesystemaccordingtothechangesinthemeasuredparameters,theenvironmentandthecostofrawmaterials,sothatthesystemisinthebeststateatanytime.Adaptivecontrolincludesthreelinks:performanceestimation(discrimination),decision-makingandmodification.Itisthedevelopmentdirectionofthemicrocomputercontrolsystem.However,becausethecontrollawisdifficulttograsp,therearestillsomedifficultproblemstopromote.
Addingadaptivepidcontrolbringssomeintelligentfeatures,whichcanadapttochangesinexternalconditionslikeacreature.
Има и система за самообучение, която я прави по-интелигентна.
Ефективност на контролера
Проблем в PID контрола
Therearedocumentsthatpointoutthat60%ofcontrollersintheactualindustryhaveperformanceproblems.Intheindustrialprocess,thereasonsforthepoorperformanceofthecontrolloopcanbeattributedtooneormoreofthefollowingsituations:1)Thecontrollerispoorlytunedandlacksmaintenance.Thereasonsforthissituationinclude:thecontrollerhasneverbeentunedoristunedbasedonamismatchmodel,oranimpropertypeofcontrollerhasbeenused.Intheindustrialprocessautomaticcontrolsystem,morethan90%ofthecontrollersarePIDtypecontrollers,evenifothercontrollersmaybeusedinsomecases,betterperformancemaybeobtained.Infact,themostcommoncauseofpoorcontrolloopperformanceisthelackofmaintenanceofthecontroller.Afteryearsofoperation,thedynamiccharacteristicsoftheactuatorandthecontrolledobjectmaychangeduetowearandotherreasons.Onlyafewengineersmaintainthecontrolloop,andoperatorsandengineersoftenlackunderstandingofthereasonsforthepoorperformanceofthecontrolloop.
2)Equipmentfailureorunreasonablestructuredesign.Poorcontrolloopperformancemaybecausedbysensororactuatorfailure(suchasexcessivefriction).Ifthedesignoftheindustrialdeviceorthecomponentsofthedeviceisnotreasonable,theproblemmaybemoreserious.Theseproblemscannotbeeffectivelysolvedbyre-tuningthecontroller.
3)Lackorinsufficientfeedforwardcompensation.Ifhandledimproperly,externaldisturbanceswilldeterioratetheperformanceoftheloop.Therefore,whenthedisturbanceismeasurable,itisrecommendedtouseFeedforvvardControl(FFC)tocompensateforthedisturbance.
4)Thecontrolstructuredesignisunreasonable.Inappropriateinput/outputpairing,ignoringthemutualcouplingbetweensystemvariables,CompetingControllers,insufficientdegreesoffreedom,strongnonlinearity,andlackofcompensationforlargetimedelaysmayallleadtocontrolstructureproblems.
Оценка на производителността на PID контрола
ExistingdocumentshavepointedoutthatitisfeasibletoestimatetheminimumvariancethatcanbeachievedbyPIDcontrolwithconventionaloperatingdatainaknownprocess;forPIDcontrol,itcanbeachievedbyusingPIDAstheevaluationbenchmark,theevaluationresultsaremorereasonable;thePIDcontrollerparametersestimatedafterfittingthemodelcansignificantlyreducetheprocessoutputvariance.
Controlperformancemonitoring/assessment(CPM/CPA)forcontrolsystemsisoneofthemostconcernedresearchdirectionsintheworldofprocesscontrol.ControllerperformancemonitoringandevaluationcanbetracedbacktotheworkofAstrom(1967),DeVrieWu(1978)andothersinthe1960sand1970s;by1970,Box,Jenkins(1976),Astrominimumvariancecontrol(minimumvariancecontrol),MVC);In1989,Harris(1989)usedtheminimumvariancecontroltoevaluatethevarianceperformanceoftheSISOsystem,whichmadethisfieldhavepioneeringresultsandnewgoalsinrandomperformancemonitoringandevaluation.Sincethen,CPM/CPAtechnologyhasattractedtheattentionandresearchofalargenumberofcontroltheoryscholarsandhasachievedrapiddevelopment.Throughtheeffortsofpredecessors,thistechnologyhasdevelopedintoacross-integratedtechnologyinvolvingcontroltheory,systemidentification,signalprocessing,probabilityandstatistics,etc.Itisusuallyreferredtoastheperformancemonitoringandevaluationofthecontrolloop,andtheperformancemonitoringandevaluationofthecontroller.Evaluation,performanceevaluation,etc.
InordertosolvetheproblemofPIDcontrollerloopperformancedegradationcausedbysystemtime-varyingintheindustrialsystem,LiuXiaoyanofZhejiangUniversityputforwardthePIDaccessibilityevaluationbenchmarkproposedbyEdgar.Amethodforperformanceevaluation,optimizationandmonitoringofPIDcontrollers,namely:PIDloopevaluationoptimizationalgorithm.Thealgorithmusestheclosed-loopinputandoutputdataofthesystemtoperformonlineslidingwindowidentification,usestheMVC(MinimumVarianceControl)-basedPIDminimumvarianceaccessibilitycriteriontoevaluatetheperformanceofthePIDcontroller,andcalculatestheoptimalPIDcontrollerparametersinthesenseoftheminimumvariance;Comparethetheoreticalminimumvariancewiththeoutputvarianceasthestart-stopthresholdforonlineoptimizationofthePIDsystem.Simulationhasproveditseffectiveness.