PID中英文对照翻译.docx
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PID中英文对照翻译
中英文互译
PIDControl
Introduction
ThePIDcontrolleristhemostcommonformoffeedback。
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.
6。
2TheAlgorithm
WewillstartbysummarizingthekeyfeaturesofthePIDcontroller。
The“textbook”versionofthePIDalgorithmisdescribedby：
6.1
whereyisthemeasuredprocessvariable，rthereferencevariable，uisthecontrolsignalandeisthecontrolerror（e=
−y）.Thereferencevariableisoftencalledthesetpoint。
Thecontrolsignalisthusasumofthreeterms：
theP—term（whichisproportionaltotheerror），theI-term（whichisproportionaltotheintegraloftheerror），andtheD—term（whichisproportionaltothederivativeoftheerror）.ThecontrollerparametersareproportionalgainK，integraltimeTi,andderivativetimeTd。
Theintegral，proportionalandderivativepartcanbeinterpretedascontrolactionsbasedonthepast，thepresentandthefutureasisillustratedinFigure2.2。
ThederivativepartcanalsobeinterpretedaspredictionbylinearextrapolationasisillustratedinFigure2.2.Theactionofthedifferenttermscanbeillustratedbythefollowingfigureswhichshowtheresponsetostepchangesinthereferencevalueinatypicalcase。
EffectsofProportional，IntegralandDerivativeAction
ProportionalcontrolisillustratedinFigure6。
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。
PIDControl
Figure6。
1
Figure6。
2
DerivativeactionsceasetobeeffectivewhenTdislargerthana1s（onesixthoftheperiod）.Alsonoticethattheperiodofoscillationincreaseswhenderivativetimeisincreased.
APerspective
ThereismuchmoretoPIDthanisrevealedby（6.1）。
Afaithfulimplementationoftheequationwillactuallynotresultinagoodcontroller。
ToobtainagoodPIDcontrolleritisalsonecessarytoconsider。
Figure6.3
∙Noisefilteringandhighfrequencyrolloff
∙Setpointweightingand2DOF
∙Windup
∙Tuning
∙Computerimplementation
InthecaseofthePIDcontrollertheseissuesemergedorganicallyasthetechnologydevelopedbuttheyareactuallyimportantintheimplementationofallcontrollers。
Manyofthesequestionsarecloselyrelatedtofundamentalpropertiesoffeedback,someofthemhavebeendiscussedearlierinthebook。
6.3FilteringandSetPointWeighting
Differentiationisalwayssensitivetonoise。
ThisisclearlyseenfromthetransferfunctionG（s）=sofadifferentiatorwhichgoestoinfinityforlarges。
Thefollowingexampleisalsoilluminating。
wherethenoiseissinusoidalnoisewithfrequencyw。
Thederivativeofthesignalis
Thesignaltonoiseratiofortheoriginalsignalis1/anbutthesignaltonoiseratioofthedifferentiatedsignalisw/an.Thisratiocanbearbitrarilyhighifwislarge。
Inapracticalcontrollerwithderivativeactionitistherefornecessarytolimitthehighfrequencygainofthederivativeterm.Thiscanbedonebyimplementingthederivativetermas
6.2
insteadofD=sTdY。
Theapproximationgivenby（6。
2）canbeinterpretedastheidealderivativesTdfilteredbyafirst—ordersystemwiththetimeconstantTd/N。
Theapproximationactsasaderivativeforlow—frequencysignalcomponents。
Thegain,however，islimitedtoKN。
Thismeansthathigh-frequencymeasurementnoiseisamplifiedatmostbyafactorKN.TypicalvaluesofNare8to20。
Furtherlimitationofthehigh-frequencygain
ThetransferfunctionfrommeasurementytocontrolleroutputuofaPIDcontrollerwiththeapproximatederivativeis
Thiscontrollerhasconstantgain
athighfrequencies。
ItfollowsfromthediscussiononrobustnessagainstprocessvariationsinSection5。
5thatitishighlydesirabletorolloffthecontrollergainathighfrequencies。
Thiscanbeachievedbyadditional
lowpassfilteringofthecontrolsignalby
whereTfisthefiltertimeconstantandnistheorderofthefilter.ThechoiceofTfisacompromisebetweenfilteringcapacityandperformance。
ThevalueofTfcanbecoupledtothecontrollertimeconstantsinthesamewayasforthederivativefilterabove。
Ifthederivativetimeisused，Tf=Td/Nisasuitablechoice。
IfthecontrollerisonlyPI,Tf=Ti/Nmaybesuitable。
Thecontrollercanalsobeimplementedas
6。
3
ThisstructurehastheadvantagethatwecandevelopthedesignmethodsforanidealPIDcontrolleranduseaniterativedesignprocedure。
ThecontrollerisfirstdesignedfortheprocessP（s）。
ThedesigngivesthecontrollerparameterTd.AnidealcontrollerfortheprocessP（s）/（1+sTd/N）2isthendesignedgivinganewvalueofTdetc。
Suchaprocedurewillalsogiveaclearpictureofthetradeoffbetweenperformanceandfiltering。
SetPointWeighting
Whenusingthecontrollawgivenby（6.1）itfollowsthatastepchangeinthereferencesignalwillresultinanimpulseinthecontrolsignal。
Thisisoftenhighlyundesirablethereforderivativeactionisfrequentlynotappliedtothereferencesignal.Thisproblemcanbeavoidedbyfilteringthereferencevaluebeforefeedingittothecontroller。
Anotherpossibilityistoletproportionalactionactonlyonpartofthereferencesignal。
Thisiscalledsetpointweighting。
APIDcontrollergivenby（6。
1）thenbecomes
6。
4
wherebandcareadditionalparameter。
Theintegraltermmustbebasedonerrorfeedbacktoensurethedesiredsteadystate。
ThecontrollergivenbyD6。
4Ehasastructurewithtwodegreesoffreedombecausethesignalpathfromytouisdifferentfromthatfromrtou。
Thetransferfunctionfromrtouis
6.5
Timet
Figure6。
4Responsetoastepinthereferenceforsystemswithdifferentsetpointweightsb=0dashed,b=0.5fullandb=1.0dashdotted。
TheprocesshasthetransferfunctionP（s）=1/（s+1）3andthecontrollerparametersarek=3,ki=1.5andkd=1.5。
andthetransferfunctionfromytouis
6。
6
Setpointweightingisthusaspecialcaseofcontrollershavingtwodegreesoffreedom.
Thesystemobtainedwiththecontroller（6.4）respondtoloaddisturbancesandmeasurementnoiseinthesamewayasthecontroller（6.1）。
Theresponsetoreferencevaluescanbemodifiedbytheparametersbandc。
ThisisillustratedinFigure6。
4,whichshowstheresponseofaPIDcontrollertoset—pointchanges，loaddisturbances,andmeasurementerrorsfordifferentvaluesofb。
Thefigureshowsclearlytheeffectofchangingb。
Theovershootforset-pointchangesissmallestforb=0,whichisthecasewherethereferenceisonlyintroducedintheintegralterm，andincreaseswithincreasingb。
Theparametercisnormallyzerotoavoidlargetransientsinthecontrolsignalduetosuddenchangesintheset—point.
6。
4DifferentParameterizations
ThePIDalgorithmgivenbyEquation（6。
1）canberepresentedbythetransferfunction
6.7
6。
8
6。
9
AninteractingcontrolleroftheformEquationD6。
8Ethatcorrespondstoanon—interactingcontrollercanbefoundonlyif
Theparametersarethengivenby
6。
10
Thenon—interactingcontrollergivenbyEq
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