计算机控制技术-(2.5、2.6、3.1、3.2)ppt课件.ppt

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1、HowtoselectsamplingcycletimeControlperformance,anti-disturbancequickresponseActuatorcharacteristics,computingloadcostDemandsfromdifferentviewpoints-------faster-------slowerTheoretically:Shannon’stheoremTorestoretheoriginalcontinuoussignal,thesamplingrate

2、shouldsatisfytheeqt.Practically,toselectthesamplinginterval,thefollowinginfluentialfactorsshouldbetakenintoaccount1.frequencyofmaindisturbancetotheplant.2.dominanttimeconst.oftheplant.3.responsespeedofactuator.----shorter----shorter(e.g.servovalve100Hzban

3、dwidth.-->Looptime10ms)4.Requiredaccuracy/responsespeed(Tsperformance)5.Ratioofperformancetocost6.Computingload(numberofloopsTs)Therefore,determiningsamplingrateisatrade-offoption.Normally,wechoose:Timeconst.oftheplant[ifnotimedelayor<0.5Tp][if0.5Tp]Ifpra

4、ctical,Tsshouldbechosenassmallaspossible2.4ApplicationsofDigitalPIDControllerIntroducehowthePIDcontrollersareincorporatedintoacontrolsystem1)Single—loopPIDcontrol“PID”couldbeahardwaredevicewithdigitalPIDcontrolfunctionorsimplyacontrolprogramrunningincompu

5、terPIDD/AplantA/Dr(t)+-e(t)u(t)c(t)2)CascadecontrolsystemFeatures:1.twoPIDcontrollers,twocontrolloops(innerloopandouterloop)2.u1istheref.signalofinnerloop3.asynchronous/synchronoussamplingcontrolDecidedbyinnerloopsamplingratePID1A/Dr(k)+_+PID2D/Aplant1A/D

6、_plant2Merits:Reducesensitivitytothedisturbancesandpara.changeintheinnerloopCompensatetheinnerloopinertiatoimprovesystemresponse3)Feedforward—feedbacksystemPIDG(s)D/AA/Dr(k)+-++e(k)Ud(f)++c(t)d(t):disturbanceNotice:[deviation/errorcontrol+disturbancecontr

7、ol]Tomaked(t)beingcompensatedcompletely:[ignoringD/Aeffect]Notes:①Inpractice,verydifficulttorealize.however,partialcompensationhelps.②Havetoknowthesystemmodelforfeedforwardcompensation→onlytrueforlimitedcases.2.5DigitalControloftheSystemswithtimedelayWhe

8、re/whythetimedelayappears:①Transportationofmaterialsortransferofenergyneedtime→timedelay.②Incontrolsystemdesignpractice,high-ordersystemsareapproximatedbyafirst-orderlagwithtimedelay.Problemcaused:timedelay→delayedc