Peruskatsaus
PID-säädin(ProportionIntegrationDifferentiation.ProportionIntegrationDifferentiation.Proportion-Integration-DifferentiationController),joka koostuu suhteellisesta yksiköstäP,integralunitIandderivativemittersofthrought,Kposition. ID-ohjaimetsoveltuvat pääasiassa järjestelmiin, joiden peruslineaarisuus ja dynaamiset ominaisuudet eivät muutu ajan myötä.
PIDcontrollerisacommonfeedbackloopcomponentinindustrialcontrolapplications.Thiscontrollercomparesthecollecteddatawithareferencevalue,andthenusesthisdifferencetocalculateanewinputvalue.Thepurposeofthisnewinputvalueistoallowthesystemdatatoreachormaintainthereferencevalue.Differentfromothersimplecontrolcalculations,PIDcontrollercanadjusttheinputvalueaccordingtohistoricaldataandtheoccurrencerateofdifference,whichcanmakethesystemmoreaccurateandmorestable.ItcanbeprovedbymathematicalmethodsthataPIDfeedbackloopcankeepthesystemstablewhenothercontrolmethodsleadtosystemstabilityerrorsorprocessrepetitions.
Palautesilmukka
Ohjaussilmukka koostuu kolmesta osasta:
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:
Osuus-Virran ohjaamiseksi virhearvo kerrotaan negatiivisella vakiollaP(osuus)ja sitten ennalta määrättyLisää .Esimerkiksi sähkövahvistimen säätimen asteikko on10° C,ja sen ennalta määrätty arvo on20 °C.Sillointulostaa100% 10 °C:ssa, 50% 15 °C:ssa ja 10% 19 °C:ssa.Huomaa, että jos virhe on0,säätimen lähtö on0.
Integration-Tocontrolthepast,theerrorvalueisthesumoftheerrorsinthepastperiodoftime,andthenmultipliedbyanegativeconstantI,andthencomparedwiththepredeterminedvalueadd.IFindtheaverageerrorbetweentheoutputresultofthesystemandthepredeterminedvaluefromtheaverageerrorvalueinthepast.Asimpleproportionalsystemwilloscillateandchangebackandfortharoundapredeterminedvaluebecausethesystemcannoteliminateredundantcorrections.Byaddinganegativeaverageerrorratiovalue,theaveragesystematicerrorvaluewillalwaysdecrease.Therefore,intheend,thePIDloopsystemwillbesetatapredeterminedvalue.
Johdannainen-Jos haluat hallita tulevaisuutta, laske virheenensimmäinen johdannainen, kerro se negatiivisella vakiollaD ja lisää lopuksi ennalta määrättyyn arvoon. Tämän johdannaisen ohjaus reagoi järjestelmän muutoksiin. parametrit ovat myös siitä syystä, että PID:tä kutsutaan ennustettavaksi ohjaimeksi.D parametrit ovat erittäin hyödyllisiävähentämäänlyhytaikaisia ohjaimenmuutoksia. Käytännössä jotkut hitaat järjestelmät eivät välttämättä vaadiD-parametria. Ammattimaisemmissa ehdoissa PID-ohjain voidaan kutsua suodattimeksi taajuusalueen pääjärjestelmässä. ohjausjärjestelmän syöttöarvo heilahtelee toistuvasti, mikä voi aiheuttaa sen, että järjestelmä saavuttaa aina esiasetetun arvon.
Ohjauslaki
Vaikka erityyppisillä ohjaimilla on erilaisia rakenteita ja periaatteita, on olemassa vain kolmeperussäätölakia: suhteellinen(P)ohjaus, integraalinen(I)ohjausJa johdannainen(D)ohjaus.Näitä ohjauslakeja voidaankäyttääyksin,mutta)yhteydessä tai yhteiskäytössä. tional-integral(PI)ohjaus,suhteellinen -integraalijohdannainen (PID) ohjaus jne.
Suhteellinen (P)ohjaus
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.
Suhteellisen integraalin (PI) ohjaus
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.
Suhteellisen johdannaisen (PD) ohjaus
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-ohjaus
Themostidealcontrolistheproportional-integral-derivativecontrollaw.Itcombinestheadvantagesofthethree:boththeproportionalactionistimelyandrapid,theintegralactioncaneliminatetheresidualerror,andthedifferentialactionhastheadvancedcontrolfunction.
Whenthedeviationstepoccurs,thederivativewillactimmediatelytosuppressthisleapofdeviation;theratioalsoplaysaroleineliminatingthedeviation,sothatthedeviationrangeisreduced,becausetheproportionaleffectislastingandeffective.Themaineffectofthecontrollaw,sothatthesystemcanbemorestable;andtheintegraleffectgraduallyovercomestheresidualerror.Aslongasthecontrolparametersofthethreefunctionsareselectedproperly,theadvantagesofthethreecontrollawscanbefullyutilizedandamoreidealcontroleffectcanbeobtained.
Virheenkorjausmenetelmä
Suhteellisuuskertoimen säätö
Suhteellisuuskertoimen säätöalue on yleensä 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.
Adaptiivinen hallinta
Ensinnäkin, selvitä mikä on mukautuva ohjaus
Intheproductionprocess,inordertoimproveproductquality,increaseoutput,saverawmaterials,productionmanagementandTheproductionprocessisalwaysinoptimalworkingcondition.Therefore,anoptimalcontrolmethodisproduced,whichiscalledadaptivecontrol.Inthiskindofcontrol,thesystemisrequiredtobeabletoautomaticallyadjustthesystemaccordingtothechangesinthemeasuredparameters,theenvironmentandthecostofrawmaterials,sothatthesystemisinthebeststateatanytime.Adaptivecontrolincludesthreelinks:performanceestimation(discrimination),decision-makingandmodification.Itisthedevelopmentdirectionofthemicrocomputercontrolsystem.However,becausethecontrollawisdifficulttograsp,therearestillsomedifficultproblemstopromote.
Addingadaptivepidcontrolbringssomeintelligentfeatures,whichcanadapttochangesinexternalconditionslikeacreature.
On myös itseoppimisjärjestelmä, joka tekee siitä älykkäämmän.
Säätimen suorituskyky
PID-ohjauksen ongelmat
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.
PID-suorituskyvyn arviointi
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.