外文文献及翻译基于matlabddesimulink力控的液位控制系统.docx

外文文献及翻译基于matlabddesimulink力控的液位控制系统.docx

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外文文献及翻译基于matlabddesimulink力控的液位控制系统

外文翻译

Theliquidlevelcontrolsystembasedondde\matlab\simulink

Processcontrolisanimportantapplicationfieldofautomatictechnology,itistopointtothelevel,temperature,flowcontrolprocessvariables,suchasinmetallurgy,machinery,chemical,electricpower,etccanbewidelyused.Especiallyliquidlevelcontroltechnologyinreallife,playedanimportantroleinproduction,forexample,thewatersupply,civilwatertoweriflowwaterlevels,canaffectpeople'slivesinwater;Industrialenterpriseswithwater,ifthedrainagewaterdrainageorcontrolledproperlyornot,inrelationtotheworkshopofcondition;Boilerdrum,ifthecontrollevelboileristoolow,canmakelevelboileroverheating,possibleaccident;Jingflow,liquidlevelcontroltowercontrolaccuracyandlevelofthecraftcaninfluencethequalityoftheproductsandthecost,etc.Intheseproductionfield,arebasicallylaborstrengthortheoperationhascertainrisknatureofwork,extremelypronetoaccidentscausedbyoperatingerror,thelosses,killingmanufacturer.Visible,inactualproduction,liquidlevelcontrolaccuracyandcontroleffectsdirectlyaffectthefactoryproductioncostandeconomicbenefitofsafetycoefficient.EvenequipmentSo,inordertoensuresafety,convenientoperation,youhavetoresearchthedevelopmentofadvancedlevelcontrolmethodsandstrategies.

Thegraduationdesigntopicistheliquidlevelcontrolsystembasedondde\matlab\simulink\forcecontrol,Amongthemwascontrolledobjectfortanklevel,CommunicationmodeforDDEcommunications,Matlabismainlyusedinthesimulationtest,Andforcecontrolsoftwareusedformodeling,Thissystemmainlythroughcombinationofhardwareandsoftwaredevicetoachieveprecisecontrolofliquidlevel,Inmodernindustrylevelcontrolofimportantcomponent,itinfluenceuponproductionnotallowtoignore,inordertoensuresafetyinproductionandtheproductqualityandquantity,thelevelandperformeffectivecontrolisverynecessary,Thefollowingisadescriptionofallaspects：

一PIDcontroller

Aproportional–integral–derivativecontroller（PIDcontroller）isageneric.controlloopfeedbackmechanismwidelyusedinindustrialcontrolsystems.APIDcontrollerattemptstocorrecttheerrorbetweenameasuredprocessvariableandadesiredsetpointbycalculatingandthenoutputtingacorrectiveactionthatcanadjusttheprocessaccordingly.

ThePIDcontrollercalculation（algorithm）involvesthreeseparateparameters;theProportional,theIntegralandDerivativevalues.TheProportionalvaluedeterminesthereactiontothecurrenterror,theIntegraldeterminesthereactionbasedonthesumofrecenterrorsandtheDerivativedeterminesthereactiontotherateatwhichtheerrorhasbeenchanging.Theweightedsumofthesethreeactionsisusedtoadjusttheprocessviaacontrolelementsuchasthepositionofacontrolvalveorthepowersupplyofaheatingelement.By"tuning"thethreeconstantsinthePIDcontrolleralgorithmthePIDcanprovidecontrolactiondesignedforspecificprocessrequirements.Theresponseofthecontrollercanbedescribedintermsoftheresponsivenessofthecontrollertoanerror,thedegreetowhichthecontrollerovershootsthesetpointandthedegreeofsystemoscillation.NotethattheuseofthePIDalgorithmforcontroldoesnotguaranteeoptimalcontrolofthesystemorsystemstability.

Someapplicationsmayrequireusingonlyoneortwomodestoprovidetheappropriatesystemcontrol.Thisisachievedbysettingthegainofundesiredcontroloutputstozero.APIDcontrollerwillbecalledaPI,PD,PorIcontrollerintheabsenceoftherespectivecontrolactions.PIcontrollersareparticularlycommon,sincederivativeactionisverysensitivetomeasurementnoise,andtheabsenceofanintegralvaluemaypreventthesystemfromreachingitstargetvalueduetothecontrolaction.

1.Controlloopbasics

Afamiliarexampleofacontrolloopistheactiontakentokeepone'sshowerwaterattheidealtemperature,whichtypicallyinvolvesthemixingoftwoprocessstreams,coldandhotwater.Thepersonfeelsthewatertoestimateitstemperature.Basedonthismeasurementtheyperformacontrolaction:

usethecoldwatertaptoadjusttheprocess.Thepersonwouldrepeatthisinput-outputcontrolloop,adjustingthehotwaterflowuntiltheprocesstemperaturestabilizedatthedesiredvalue.

Feelingthewatertemperatureistakingameasurementoftheprocessvalueorprocessvariable（PV）.Thedesiredtemperatureiscalledthesetpoint（SP）.Theoutputfromthecontrollerandinputtotheprocess（thetapposition）iscalledthemanipulatedvariable（MV）.Thedifferencebetweenthemeasurementandthesetpointistheerror（e）,toohotortoocoldandbyhowmuch.Asacontroller,onedecidesroughlyhowmuchtochangethetapposition（MV）afteronedeterminesthetemperature（PV）,andthereforetheerror.ThisfirstestimateistheequivalentoftheproportionalactionofaPIDcontroller.TheintegralactionofaPIDcontrollercanbethoughtofasgraduallyadjustingthetemperaturewhenitisalmostright.Derivativeactioncanbethoughtofasnoticingthewatertemperatureisgettinghotterorcolder,andhowfast,andtakingthatintoaccountwhendecidinghowtoadjustthetap，Makingachangethatistoolargewhentheerrorissmallisequivalenttoahighgaincontrollerandwillleadtoovershoot.Ifthecontrollerweretorepeatedlymakechangesthatweretoolargeandrepeatedlyovershootthetarget,thiscontrolloopwouldbetermedunstableandtheoutputwouldoscillatearoundthesetpointineitheraconstant,growing,ordecayingsinusoid.Ahumanwouldnotdothisbecauseweareadaptivecontrollers,learningfromtheprocesshistory,butPIDcontrollersdonothavetheabilitytolearnandmustbesetupcorrectly.Selectingthecorrectgainsforeffectivecontrolisknownastuningthecontroller.

Ifacontrollerstartsfromastablestateatzeroerror（PV=SP）,thenfurtherchangesbythecontrollerwillbeinresponsetochangesinothermeasuredorunmeasuredinputstotheprocessthatimpactontheprocess,andhenceonthePV.VariablesthatimpactontheprocessotherthantheMVareknownasdisturbancesandgenerallycontrollersareusedtorejectdisturbancesand/orimplementsetpointchanges.Changesinfeedwatertemperatureconstituteadisturbancetotheshowerprocess.

Intheory,acontrollercanbeusedtocontrolanyprocesswhichhasameasurableoutput（PV）,aknownidealvalueforthatoutput（SP）andaninputtotheprocess（MV）thatwillaffecttherelevantPV.Controllersareusedinindustrytoregulatetemperature,pressure,flowrate,chemicalcomposition,speedandpracticallyeveryothervariableforwhichameasurementexists.Automobilecruisecontrolisanexampleofaprocesswhichutilizesautomatedcontrol.

Duetotheirlonghistory,simplicity,wellgroundedtheoryandsimplesetupandmaintenancerequirements,PIDcontrollersarethecontrollersofchoiceformanyoftheseapplications.

2.PIDcontrollertheory

Note:

Thissectiondescribestheidealparallelornon-interactingformofthePIDcontroller.ForotherformspleaseseetheSection"AlternativenotationandPIDforms".

ThePIDcontrolschemeisnamedafteritsthreecorrectingterms,whosesumconstitutesthemanipulatedvariable（MV）.Hence:

wherePout,Iout,andDoutarethecontributionstotheoutputfromthePIDcontrollerfromeachofthethreeterms,asdefinedbelow.

2.1.Proportionalterm

Theproportionaltermmakesachangetotheoutputthatisproportionaltothecurrenterrorvalue.TheproportionalresponsecanbeadjustedbymultiplyingtheerrorbyaconstantKp,calledtheproportionalgain.

Theproportionaltermisgivenby:

Where

Pout:

Proportionaloutput

Kp:

ProportionalGain,atuningparameter

e:

Error=SP−PV

t:

Timeorinstantaneoustime（thepresent）

ChangeofresponseforvaryingKpAhighproportionalgainresultsinalargechangeintheoutputforagivenchangeintheerror.Iftheproportionalgainistoohigh,thesystemcanbecomeunstable（SeethesectiononLoopTuning）.Incontrast,asmallgainresultsinasmalloutputresponsetoalargeinputerror,andalessresponsive（orsensitive）controller.Iftheproportionalgainistoolow,thecontrolactionmaybetoosmallwhenrespondingtosystemdisturbances.

Intheabsenceofdisturbances,pureproportionalcontrolwillnotsettleatitstargetvalue,butwillretainasteadystateerrorthatisafunctionoftheproportionalgainandtheprocessgain.Despitethesteady-stateoffset,bothtuningtheoryandindustrialpracticeindicatethatitistheproportionaltermthatshouldcontributethebulkoftheoutputchange.

2.2.Integralterm

Thecontributionfromtheintegraltermisproportionaltoboththemagnitudeoftheerrorandthedurationoftheerror.Summingtheinstantaneouserrorovertime（integratingtheerror）givestheaccumulatedoffsetthatshouldhavebeencorrectedpreviously.Theaccumulatederroristhenmultipliedbytheintegralgainandaddedtothecontrolleroutput.Themagnitudeofthecontributionoftheintegraltermtotheoverallcontrolactionisdeterminedbytheintegralgain,Ki.

Theintegraltermisgivenby:

Iout:

Integraloutput

Ki:

IntegralGain,atuningparameter

e:

Error=SP−PV

τ:

Timeinthepastcontributingtotheintegralresponse

Theintegralterm（whenaddedtotheproportionalterm）acceleratesthemovementoftheprocesstowardssetpointandeliminatestheresidualsteady-stateerrorthatoccurswithaproportionalonlycontroller.However,sincetheintegraltermisrespondingtoaccumulatederrorsfromth