pid简介及英语翻译

PIDControlIntroductionThePIDcontrolleristhemostcommonformoffeedback.Itwasanessentialelementofearlygovernorsanditbecamethestandardtoolwhenprocesscontrolemergedinthe1940s.Inprocesscontroltoday,morethan95%ofthecontrolloopsareofPIDtype,mostloopsareactuallyPIcontrol.PIDcontrollersaretodayfoundinallareaswherecontrolisused.Thecontrollerscomeinmanydifferentforms.Therearestandalonesystemsinboxesforoneorafewloops,whicharemanufacturedbythehundredthousandsyearly.PIDcontrolisanimportantingredientofadistributedcontrolsystem.Thecontrollersarealsoembeddedinmanyspecialpurposecontrolsystems.PIDcontrolisoftencombinedwithlogic,sequentialfunctions,selectors,andsimplefunctionblockstobuildthecomplicatedautomationsystemsusedforenergyproduction,transportation,andmanufacturing.Manysophisticatedcontrolstrategies,suchasmodelpredictivecontrol,arealsoorganizedhierarchically.PIDcontrolisusedatthelowestlevel;themultivariablecontrollergivesthesetpointstothecontrollersatthelowerlevel.ThePIDcontrollercanthusbesaidtobethe“breadandbutterofcontrolengineering.Itisanimportantcomponentineverycontrolengineer’stoolbox.PIDcontrollershavesurvivedmanychangesintechnology,frommechanicsandpneumaticstomicroprocessorsviaelectronictubes,transistors,integratedcircuits.ThemicroprocessorhashadadramaticinfluencethePIDcontroller.PracticallyallPIDcontrollersmadetodayarebasedonmicroprocessors.Thishasgivenopportunitiestoprovideadditionalfeatureslikeautomatictuning,gainscheduling,andcontinuousadaptation.TheAlgorithmWewillstartbysummarizingthekeyfeaturesofthePIDcontroller.The“textbook”versionofthePIDalgorithmisdescribedby:dttdedeteKtuTTdti016.1whereyisthemeasuredprocessvariable,rthereferencevariable,uisthecontrolsignalandeisthecontrolerror（e=spy−y）.Thereferencevariableisoftencalledthesetpoint.Thecontrolsignalisthusasumofthreeterms:theP-term（whichisproportionaltotheerror）,theI-term（whichisproportionaltotheintegraloftheerror）,andtheD-term（whichisproportionaltothederivativeoftheerror）.ThecontrollerparametersareproportionalgainK,integraltimeTi,andderivativetimeTd.Theintegral,proportionalandderivativepartcanbeinterpretedascontrolactionsbasedonthepast,thepresentandthefutureasisillustratedinFigure2.2.ThederivativepartcanalsobeinterpretedaspredictionbylinearextrapolationasisillustratedinFigure2.2.Theactionofthedifferenttermscanbeillustratedbythefollowingfigureswhichshowtheresponsetostepchangesinthereferencevalueinatypicalcase.EffectsofProportional,IntegralandDerivativeActionProportionalcontrolisillustratedinFigure6.1.ThecontrollerisgivenbyD6.1EwithTi=andTd=0.Thefigureshowsthatthereisalwaysasteadystateerrorinproportionalcontrol.Theerrorwilldecreasewithincreasinggain,butthetendencytowardsoscillationwillalsoincrease.Figure6.2illustratestheeffectsofaddingintegral.ItfollowsfromD6.1EthatthestrengthofintegralactionincreaseswithdecreasingintegraltimeTi.Thefigureshowsthatthesteadystateerrordisappearswhenintegralactionisused.Comparewiththediscussionofthe“magicofintegralaction”inSection2.2.ThetendencyforoscillationalsoincreaseswithdecreasingTi.ThepropertiesofderivativeactionareillustratedinFigure6.3.Figure6.3illustratestheeffectsofaddingderivativeaction.TheparametersKandTiarechosensothattheclosedloopsystemisoscillatory.Dampingincreaseswithincreasingderivativetime,butdecreasesagainwhenderivativetimebecomestoolarge.RecallthatderivativeactioncanbeinterpretedasprovidingpredictionbylinearextrapolationoverthetimeTd.UsingthisinterpretationitiseasytounderstandthatderivativeactiondoesnothelpifthepredictiontimeTdistoolarge.InFigure6.3theperiodofoscillationisabout6sforthesystemwithoutderivativeChapter6.PIDControlFigure6.1Figure6.2DerivativeactionsceasetobeeffectivewhenTdislargerthana1s(onesixthoftheperiod).Alsonoticethattheperiodofoscillationincreaseswhenderivativetimeisincreased.ThereismuchmoretoPIDthanisrevealedby（6.1）.Afaithfulimplementationoftheequationwillactuallynotresultinagoodcontroller.ToobtainagoodPIDcontrolleritisalsonecessarytoconsider。Figure6.3DifferentParameterizationsThePIDalgorithmgivenbyEquation（6.1）canberepresentedbythetransferfunctionTTdissKsG116.7TTTidiKK6.8TTTdii6.9TTTTTdididAninteractingcontrolleroftheformEquationD6.8Ethatcorrespondstoanon-interactingcontrollercanbefoundonlyifTTdi4TheparametersarethengivenbyTTidKK4112TTTTidii41126.10TTTTidid4112Thenon-interactingcontrollergivenbyEquation（6.7）ismoregeneral,andwewillusethatinthefuture.Itis,however,sometimesclaimedthattheinteractingcontrolleriseasiertotunemanually.ItisimportanttokeepinmindthatdifferentcontrollersmayhavedifferentstructureswhenworkingwithPIDcontrollers.Ifacontrollerisreplacedbyanothertypeofcontroller,thecontrollerparametersmayhavetobechanged.Theinteractingandthenon-interactingformsdifferonlywhenbothIandtheDpartsofthecontrollerareused.IfweonlyusethecontrollerasaP,PI,orPDcontroller,thetwoformsareequivalent.YetanotherrepresentationofthePIDalgorithmisgivenbykkdissksG6.11TheparametersarerelatedtotheparametersofstandardformthroughKkTkiiKTk