电气专业英语教学课件作者徐志成chapter4.ppt

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1、Chapter4PrinciplesofAutomaticControlUnit17IntroductiontoControlUnit18TransferFunctionsUnit19ModesofControlUnit20ControlLoopsUnit21PIDControllerUnit17IntroductiontoControlNeedforautomaticcontrolTherearethreemajorreasonswhyprocessplantsorbuildingsrequireautomaticcontrol:(1) Safety(2) Stabilit

2、y(3) AccuracyAutomaticcontrolterminologySpecifictermsareusedwithinthecontrolindustry,primarilytoavoidconfusion.Thesamewordsandphrasescometogetherinallaspectsofcontrol,andwhenusedcorrectly,theirmeaningsareuniversal.ThesimplemanualsystemdescribedinExample4.17.1andillustratedinFig. 4.17.1isuse

3、dtointroducesomestandardtermsusedincontrolengineering.下一页返回Unit17IntroductiontoControlExample4.17.1AsimpleanalogyofacontrolsystemExample4.17.2Elementsofautomaticcontrol(Fig.4.17.2)Assessingsafety,stabilityandaccuracyItcanbeassumedthataprocesstypicalofthatinExample4.17.1containsneithervaluab

4、lenorharmfulingredients.Therefore,overfloworwaterstarvationwillbesafe,butnoteconomicorproductive.Intermsofstability,theoperatorwouldbeabletohandlethisprocessprovidinghepaysfullandconstantattention.上一页下一页返回Unit17IntroductiontoControlAccuracyisnotafeatureofthisprocessbecausetheoperatorcanonly

5、respondtoavisibleandrecognizableerror.上一页返回Unit18TransferFunctionsATransferFunctionistheratiooftheoutputofasystemtotheinputofasystem,intheLaplacedomainconsideringitsinitialconditionstobezero.IfwehaveaninputfunctionofX(s),andanoutputfunctionY(s),wedefinethetransferfunctionH(s)tobe:Impulseres

6、ponseForcomparison,wewillconsiderthetime-domainequivalenttotheaboveinput/outputrelationship.Inthetimedomain,wegenerallydenotetheinputtoasystemasx(t),andtheoutputofthesystemasy(t).下一页返回Unit18TransferFunctionsTherelationshipbetweentheinputandtheoutputisdenotedastheimpulseresponse,h(t).Wedefin

7、etheimpulseresponseasbeingtherelationshipbetweenthesystemoutputanditsinput.Wecanusethefollowingequationtodefinetheimpulseresponse:ImpulsefunctionItwouldbehandyatthispointtodefinepreciselywhatan“impulse”is.TheImpulseFunction,denotedwithd(t)isaspecialfunct