毕业设计英文翻译.docx

毕业设计英文翻译.docx

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毕业设计英文翻译

英文翻译

系别机电工程系

专业自动化

班级163803

学生姓名田琨

学号081470

指导教师张科、王敏

DesignOfFuzzyControllers

1.1Introduction

WhileitisrelativelyeasytodesignaPIDcontroller,andtheinclusionofthefuzzyrulescreatesalotofextradesignproblems,andalthoughalotofintroductorytextbooksexplainfuzzycontroltherearefewgeneralguidelinesforsettingtheparametersofasimplefuzzycontroller.

Theapproachhereisbasedonathreestepdesignprocedure,thatbuildsonPIDcontrol:

1.StartwithaPIDcontroller.

2.Insertanequivalent,linearfuzzycontroller.

3.Makeitgraduallynonlinear.

Guidelinesrelatedtothedifferentcomponentsofthefuzzycontrollerwillbeintroducedshortly.Inthenextthreesectionsthreesimplerealisationsoffuzzycontrollersaredescribed:

atable-basedcontroller,aninput-outputmappingandaTakagi-Sugenotypecontroller.Ashortsectionsummarisesthemaindesignchoicesinasimplefuzzycontrollerbyintroducingachecklist.Theterminologyisbasedonaninternationalstandardwhichisunderway（IEC,1996）.Fuzzycontrollersareusedtocontrolconsumerproducts,suchaswashingmachines,videocameras,andricecookers,aswellasindustrialprocesses,suchascementkilns,undergroundtrains,androbots.Fuzzycontrolisacontrolmethodwhichisbasedonfuzzylogic.Justasfuzzylogiccanbedescribedsimplyas“computingwithwordsratherthannumbers”,fuzzycontrolcanbedescribedsimplyas“controlwithsentencesratherthanequations”.

Afuzzycontrollercanincludetheempiricalrules,andthatisespeciallyusefulinoperatorcontrolledplants.

Takeforinstanceatypicalfuzzycontroller

1.IferrorisNegandchangeinerrorisNegthenoutputisNB

2.IferrorisNegandchangeinerrorisZerothenoutputisNM

……

Thecollectionofrulesiscalledarulebase.Therulesareinthefamiliarif-thenformat,andformallytheif-sideiscalledtheconditionandthethen-sideiscalledtheconclusion（moreoften,perhaps,thepairiscalledtheantecedent-consequentorpremise-conclusion）.Theinputvalue“Neg”isalinguisticshortforthewordNegative,theoutputvalue“NB”standsforNegativeBigand“NM”forNegabiveMeduim.Thecomputerisabletoexecutetherulesandcomputeacontrolsignaldependingonthemeasuredinputserrorandchangeinerror.

Theobjectivehereistoidentifyandexplainthevariousdesignchoicesforengineers.

Inarulebasedcontrollerthecontrolstrategyisstoredinamoreorlessnaturallanguage.Thecontrolstrategyisisolatedinarulebaseopposedtoanequationbaseddescription.Arulebasedcontrolleriseasytounderstandandeasytomaintainforanon-specialistend-user.Anequivalentcontrollercouldbeimplementedusingconventionaltechniquesinfact,anyrulebasedcontrollercouldbeemulatedin,say,Fortran-itisjustthatitisconvenienttoisolatethecontrolstrategyinarulebaseforoperatorcontrolledsystems.

Fuzzycontrollersarebeingusedinvariouscontrolschemes（IEC,1996）.Themostobviousoneisdirectcontrol,wherethefuzzycontrollerisintheforwardpathinafeedbackcontrolsystem.Theprocessoutputiscomparedwithareference,andifthereisadeviation,thecontrollertakesactionaccordingtothecontrolstrategy.Inthefigure,thearrowsmaybeunderstoodashyper-arrowscontainingseveralsignalsatatimeformultiloopcontrol.Thesub-componentsinthefigurewillbeexplainedshortly.Thecontrollerishereafuzzycontroller,anditreplacesaconventionalcontroller,say,aPID（proportional-integral-derivative）controller.

Infeedforwardcontrol（Fig.1）ameasurabledisturbanceisbeingcompensated.Itrequiresagoodmodel,butifamathematicalmodelisdifficultorexpensivetoobtain，afuzzymodelmaybeuseful.Figure1showsacontrollerandthefuzzycompensator,theprocessandthefeedbackloopareomittedforclarity.Thescheme,disregardingthedisturbanceinput,canbeviewedasacollaborationoflinearandnonlinearcontrolactions;thecontrollerCmaybealinearPIDcontroller,whilethefuzzycontrollerFisasupplementarynonlinearcontroller.

Fuzzyrulesarealsousedtocorrecttuningparametersinparameteradaptivecontrolschemes（Fig.2）.Ifanonlinearplantchangesoperatingpoint,itmaybepossibletochangetheparametersofthecontrolleraccordingtoeachoperatingpoint.Thisiscalledgainschedulingsinceitwasoriginallyusedtochangeprocessgains.Againschedulingcontrollercontainsalinearcontrollerwhoseparametersarechangedasafunctionoftheoperatingpointinapreprogrammedway.Itrequiresthoroughknowledgeoftheplant,butitisoftenagoodwaytocompensatefornonlinearitiesandparametervariations.Sensormeasurementsareusedasschedulingvariablesthatgovernthechangeofthecontrollerparameters,oftenbymeansofatablelook-up.

Whetherafuzzycontroldesignwillbestableisasomewhatopenquestion.Stablityconcernsthesystem’sabilitytoconvergeorstayclosetoanequilibrium.Astablelinearsystemwillconvergetotheequilibriumasymptoticallynomatterwherethesystemstatevariablesstartfrom.Itisrelativelystraightforwardtocheckforstabilityinlinearsystems,forexamplebycheckingthatalleigenvaluesareinthelefthalfofthecomplexplane.Fornonlinearsystems,andcheckingthatalleigenvaluesareinthelefthalfofthecomplexplane.Fornonlinearsystems,andfuzzysystemsaremostoftennonlinear,thestabilityconceptismorecomplex.Anonlinearsystemissaidtobeasymptoticallystableif,whenitstartsclosetoanequilibrium,itwillconvergetoit.Evenifitjuststaysclosetotheequilibrium,withoutconvergingtoit,itissaidtobestable（inthesenseofLyapunov）.Tocheckconditionsforstabilityismuchmoredifficultwithnonlinearsystems,partlybecausethesystembehaviourisalsoinfluencedbythesignalamplitudesapartfromthefrequencies.TheliteratureissomewhattheoreticalandinterestedreadersarereferredtoDriankov,Hellendoorn&Reinfrank（1993）orPassino&Yurkovich（1998）.Theyreportonfourmethods（

Lyapunovfunctions,Popov,circle,andconicity）,andtheygiveseveralreferencestoscientificpapers.

Figure1：

Feedforwardcontrol

Itischaracteristic,however,thatthemethodsgiveratherconservativeresults,whichtranslateintounrealisticallysmallmagnitudesofthegainfactorsinordertoguaranteestability.Anotherpossibilityistoapproximatethefuzzycontrollerwithalinearcontroller,andthenapplytheconventionallinearanalysisanddesignproceduresontheapproximation.Itseemslikelythatthestabilitymarginsofthenonlinearsystemwouldbecloseinsomesensetothestabilitymarginsofthelinearapproximationdependingonhowclosetheapproximationis.Thispapershowshowtobuildsuchalinearapproximation,butthetheoreticalbackgroundisstillunexplored.

Thereareatleastfourmainsourcesforfindingcontrolrules（Takagi&SugenoinLee,1990）.

1.Expertexperienceandcontrolengineeringknowledge.Oneclassicalexampleistheoperator’shandbookforacementkiln（Holmblad&Ostergaard,1982）.Themostcommonapproachtoestablishingsuchacollectionofrulesofthumb,istoquestionexpertsoroperatorsusingacarefullyorganizedquestionnaire.

2.Basedontheoperator’scontrolactionrulescanbededucedfromobservationsofanoperator’scontrolactionsoralogbook.Thisrulesexpressinput-outputrelationships.

Figure2：

Fuzzyparameteradaptivecontrol

3.Basedonafuzzymodeloftheprocess.Alinguisticrulebasemaybeviewedasaninversemodelofthecontrolledprocess.Thusthefuzzycontrolrulesmightbeobtainedbyinvertingafuzzymodeloftheprocess.Thismethodisrestrictedtorelativelylowordersystems,butitprovidesanexplicitsolutionassumingthatfuzzymodelsoftheopenandclosedloopsystemsareavailable（Braae&RutherfordinLee,1990）.Anotherapproachisfuzzyidentification（Tong;Takagi&Sugeno;Sugeno–allinLee,1990;Pedrycz,1993）orfuzzymodel-basedcontrol（seelater）.

4.Basedonlearning.Theself-organisingcontrollerisanexampleofacontrollerthatfindstherulesitself.Neuralnetworksisanotherpossibility.

Thereisnodesignprocedureinfuzzycontrolsuchasroot-locusdesignandthe

frequencyresponsedesign,poleplacementdesign,orstabilitymargins,becausetherulesareoftennonlinear.Thereforewewillsettlefordescribingthebasiccomponentsandfunctionsoffuzzycontrollers,inordertorecogniseandunderstandthevariousoptionsincommercialsoftwarepackagesforfuzzycontrollerdesign.

Thereismuchliteratureonfuzzycontrolandmanycommercialsoftwaretools（MIT,1995）,butthereisnoagreementontheterminology,whichisconfusing.Thereareefforts,however,tostandardisetheterminology,andthefollowingmakesuseofadraftofastandardfromtheInternationalElectrotechnicalCommittee（IEC,1996）.Throughout,lettersdenotingmatricesareinbolduppercase,forexampleA;vectorsareinboldlowercase,forexampleX;scalarsareinitalics,forexamplen;andoperationsareinbold,forexamplemin.

1.2Structureofafuzzycontroller

Therearespecificcomponentscharacteristicofafuzzycontrollertosupportadesignprocedure.IntheblockdiagraminFig.3,thecontrollerisbetweenapreprocessingblockandapost-processingblock.Thefollowingexplainsthediagramblockbyblock.

Figure3:

Blocksofafuzzycontroller.

1.3Preprocessing

Theinputsaremostoftenhardorcrispmeasurementsfromsomemeasuringequipment,ratherthanlinguistic.Apreprocessor,thefirstblockinFig.3,conditionsthemeasurementsbeforetheyenterthecontroller.Examplesofpreprocessingare:

1.Quanti