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1、PIDTHEORYContentsWhat’sPIDPIDconceptPIDadvantagePIDtheoryExampleComplexcontrolloopWhat’sPIDcontrolsystem?Onecontrolsystemcomprisescontroller,sensor,executerunit,objectandI/Ounit.Forthedifferentcontrolsystem,sensor,executeraredifferent.Pressure,temperature,level,flowandsoon…PIDcontrolsystemusePIDalg
2、orithmtorealizecontrol.Close-loopcontrolsystemThebasicfunctionofclosed-loopcontrolistomaintainaprocesscharacteristic(temperature,flow,pressure,speed,torque)atadesiredvalue.Theprocesscandeviatefromthisdesiredsetpoint(SP)valueasaresultofchangingmaterial,loadrequirements,interactionwithotherprocesses,
3、andsoon.Theactualconditionoftheprocesscharacteristicmeasuredistheprocessvariable(PV).Thedeviationofthemeasuredprocessvariablefromthedesiredsetpointistheerror(E).Theformulaforprocesserroristhus:E=SP–PVOnceanerrorisdetermined,thefunctionofthecontrolloopistooutputacontrolvariabletotheprocesstoforcethe
4、errorEtozero.LeveltransmitterLevelcontrollerSetpointExecutervalveLevelcontrolloopPIDconceptionP:ProportionI:Integral∫D:DerivativeThecontrollerusethreetypesalgorithmtorealizethecontrolfunction,PIDThecontrollercalculatestheintegralandderivativeoftheerrorbetweentheprocessvariableandsetpointthengenerat
5、esacontroleffortbyaddingthosetwoquantitiestotheerroritself.Auserchoosesthetuningparameters—proportionalgain(P),integralgain(I)andderivativegain(D)—togivemoreorlessweighttoeachterm,therebyadjustingthecontroller'sperformance.PIDalgorithmTheformulaOutput=P*Input+I*∫+D*d/d(t)Coefficient:P=KpI=Ki/Ti D=K
6、d·TdP,I,DfunctionP:Proportioncontrolthesimplestcontrolformat.Output=P*InputSteady-state errorI:IntegralcontrolOutput=I*∫I=Ki/TiSystem with Steady-state ErrorTi:value↑,function↑，speedD:Derivativecontrolpre-actmodeOutput=D*d/d(t)D=Kd·TdKd:value↓,function↑,precision“three-modecontrol”canincludeone,two
7、,orthreeterms,ormodes,ofcontrol.Three-modecontrolisknownasPID,whichrepresentsproportional,integral,andderivative.proportionalcontrolactionprovidesacontroloutputcomponentproportionaltothevalueoftheinstantane
