外文翻译-蒸汽发生器水位模糊控制研究

英文原文ResearchonFuzzyControlforSteamGeneratorWaterLevelThomasSowellElgianNuclearResearchCentreSCKoCENBoertang200,8-2400Mol,Belgium(Received15March2012)AbstractSinceSGlevelcontrolsystemisahighlycomplex,non-linear,time-varyingandnon-minimumphasesystem.Thefalsewaterlevelwhichiscausedbythereversethermal-dynamiceffectsknownasshrinkandswelleffects,makestheSGwaterlevelprocessdynamicsdifficulttocontrol.However,traditionalPIDmethodscannotobtainsatisfactoryeffectswhoseparametersaredifficulttobeadjustedonline.Moderncontroltheoryrelysoncontrolledplantsprecisemathematicsmodelcompletely.Thefuzzycontroltechnologydoesntrelyonprecisemathematicsmodelandhasexcellentcapabilityofadaptingtothechangedparameters.ItissuitablefortheSGwaterlevelcontrol.I.INTRODUCTIONThesteamgeneratorisoneofthemaindevicesinPWRnuclearpowerplant,inordertoensurethesafetyofnuclearpowerplantduringoperation;thesteamgeneratorswaterlevelmustbecontrolledinacertainrange.Whenthenuclearpowerplantisrunning,asthesteamfloworthewaterflowchanging,theamountofboilingbubblesinthesteamgeneratorwillchangeduetolocalpressureortemperaturechange,theinstantaneouswaterlevelshowed“falsewaterlevel”phenomenon.Theexistenceof“falsewaterlevel”madeitdifficulttocontrolthewaterlevel.Theintroductionoffeed-forwardcontroltothetraditionalsingle-loopPIDcontrolcan,inacertainextent,overcomethefalsewaterlevelphenomenon.ButtheconventionalPIDcontrolmethodintheprocessofsteamgeneratorwaterlevelcontrolhassomeshortcomings.Tothesteamgeneratorthathashighlycomplex,largetime-delayandnonlineartime-varyingcharacteristics,thePIDparameterstuningisatediousjobandthecontroleffectisverypoor.Furthermore,toachievegoodcontrolperformancestillasconditionschanging,itoftenneedstochangethePIDcontrollerparameters.ButtheanalogPIDcontrollerparametersaredifficulttoregulateonline.Fuzzycontrolisakindofnonlinearcontrolstrategybasedonfuzzyreasoning,whichexpressoperatingexperienceofskilledmanipulationmenandcommonsenserulesofinferencethroughvaguelanguage.Fuzzycontroldonotneedtoknowprecisemathematicalmodelofcontrolledobject,isnotsensitivetothechangeofprocessparameters,ishighlyrobustandcanovercomenon-linearfactors,so,fuzzycontrolhasfasterresponseandsmallerultra-tone,cangetbettercontroleffect.Basedonunderstandingabove,thispaperdesignasteamgeneratorwaterlevelfuzzycontroller,thesimulationshowsthatthecontrollerhasgoodcontrolperformanceandpracticalvalue.II.DYNAMICCHARACTERISTICSOFSTEAMGENERATORThetransferfunctionofPWRsteamgeneratorsmathematicalmodelofthegeneralformshowsbelow:()=()()+()()（1）Whereyisthesteamgeneratorwaterlevel;QWforthewaterflow;QSforthesteamflow;GW(s)fortheimpactofthewaterflowtothesteamgeneratorwaterlevel;GS(s)fortheeffectofthesteamflow(load)tothesteamgeneratorwaterlevel.Thebalanceofthesteamgeneratorwaterlevelismaintainedthroughthematchbetweenthewaterflowandsteamflow.Theprocessthatwaterlevelchangeswiththesteamfloworwaterflowchangingcanberegardedasasimpleintegrationprocess,butimpactofthewaterflowandsteamflowschangeonwaterlevelisdifferent.A.DynamicsCharacteristicsunderWaterFlowDisturbanceSupposesteamflowGSremainsunchanged,andwaterflowGWstepincreases,ontheonehandbecausethetemperatureoffeedwaterismuchlowerthanthetemperatureofsaturatedwaterinthesteamgenerator,sothat,whenfeedwaterentering,itwillabsorbalotofextraheat,thevaporphasebubblecontentswillreduce,resultinginwaterleveldecreasing;ontheotherhand,theincreaseinwaterflowGWmadeitgreaterthansteamload,andcausewaterlevelincreaseslinearly.Comprehensivetwofactors,afterthestepincreaseofthewaterflow,thewaterlevelrisehasatimedelayprocess,showingadownthenup.B.DynamicCharacteristicsunderSteamLoadDisturbanceSupposefeedwaterflowGWremainsunchanged,andsteamloadGSstepincreases,ontheonehandthewaterlevelwillflowdownbecausethesteamflowrateisgreaterthanthewaterflowrate.Ontheotherhand,asthesteamloadincreased,vaporpressureisreduced;thebubblevolumeontheliquidsurfaceincreases,causingthewaterlevelincreased.Comprehensivetwofactors,afterthestepincreaseofthesteamflowrate,thewaterleveldownhasatimedelayprocess,showingaupthendown.Theimpactonthewaterlevelofwaterfloworsteamflowsteppingdecreasedhassimilarprincipleasabove.Asanalysiscanbeseenasabove,whenthewaterfloworsteamloadchange,thewaterleveldidnotfollowthechangeimmediately,butthereisanoppositeprocessatfirst.Thisphenomenoniscalledfalsewaterlevelphenomenon.III.DESIGNOFWATERLEVELFUZZYCONTROLLERTheconventionalPIDcontrollerhasapoorcontrolperformancetothesteamgeneratorthatexist“falsewaterlevel”characteristics,showingagreaterovershootinthetrackingtime.Butawell-designedfuzzycontrollerisabletoovercomethefalsewaterlevelphenomenon,andhasgoodcontrolperformance.A.StructureofFuzzyControllerThestructureshowedinFigure1.FuzzyControllerK1ValveGW(s)Dx/dtK2GS(s)ExpectedWaterleverStreamflowWaterleverWaterFloweec+-+-+Figure1.StructureofsteamgeneratorwaterlevelfuzzycontrollerChoosethewaterlevelerror(e)andchangerateoferror(ec)asinputofthefuzzycontroller,theoutputofthefuzzycontrolleristheaddedvalueofthevalveopeningsignalu.Meanwhile,usethesteamflowfeed-forwardtoovercomethefalsewaterlevelphenomenon,usewaterflowfeedbacktoovercomefluctuationsinwatersupplyside.k1,k2werewaterflowandsteamflowtransmitterconversionfactor.Toensurethewaterflowtomatchthesteamflow,k1andk2valuesshouldbeequalto.B.Fuzzytheory,fuzzysubsetandMembershipFunctionThefuzzyAnalectsofe,ecanduare-6,6,bothwithsevenfuzzysetsNB(negativebig),NM(negativemiddle),NS(negativesmall),ZO(zero),PS(positivesmall),PM(positivemiddle)andPB(positivebig)todescribe.e,ecand,uareallusingtriangularmembershipfunction(seeFigure2).Figure2.InputandoutputvariablemembershipfunctionC.FuzzycontrolruletableTheestablishmentprincipleoffuzzycontrolrulesare:whentheerrorislarge,theoutputcontrolvolumeshouldgiveprioritytoeliminateerrorassoonaspossible;whentheerrorissmall,theoutputcontrolvolumeshouldgiveprioritytopreventovershoot.Whereecisnegative,itshowsthatwaterlevelhasarisingtrend,ifthewaterlevelishighatthistime,thenweshouldreducethevalveopeningsignal;whereas,weshouldopenthevalvemore.Throughacomprehensiveanalysisofexpertise,theestablishmentofruletableshowninTable1.Table1.FuzzycontrolruletableD.FuzzyReasoningandSolutionThisfuzzyinferencesystemusesMamdani.Thebasicpropertiesoffuzzyinferencesystemsetto:andoperationwithaverysmalloperation;oroperationusesthemaximumoperation.Usingaverysmalloperationfuzzyimplication,fuzzyrulesintegratedwithgreatoperationscenterDefuzzificationmethodused.IV.SIMULATIONEXAMPLESApressurizedwaterreactorsteamgeneratorinChineseQinshannuclearpowerstationhasempiricalmodelG1(s),G2(s)below:7%15,)28(4.0)1329(.69,.)(51PssseesGssp8%90,1438.0)2(19.3)(PssseGeecNBNMNSZOPSPMPBNBNBNBNMNMNSNSZONMNBNMNMNSNSNSZONSNMNMNSNSZOPSPSZONMNSNSZOPSPSPMPSNSNSZOPSPSPMPMPMNSNSZOPSPSPMPMPBZOPSPSPMPMPBPBwherePsdenotetheratedload.Whenloadat15%90%Ps,use(6)and(8);whenloadlessthan15%Ps,use(7)and(8).Figure3.ExpectedwaterlevelstepresponsediagramThecoefficientsinControlsystemarek1=k2=0.5.Watercontrolvalveisakingoflinearvalve,itsgainis4.Thequantitativecoefficientsofeandecare6and60respectively;thescalefactorofuis0.5.Welimitwaterflowtherangeof0kg/stotheratedflow258kg/swhensimulation.Considertheexpectedlevelstepfromtheinitial0mto10m,waterlevelresponseisshownusethesolidlineinFigure3.Forcontrastingtheincreaseeffectoffuzzycontroller,wealsocarriedoutusingthetraditionalPIDcontrolsimulation.Wecansee,comparedwithtraditionalPIDcontrol,fuzzycontrollerhasreportedsignificantimprovementsinovershoot,settlingtime,steadydegrees.V.CONCLUSIONThispaperdesignedawaterlevelfuzzycontrolsystemaimedatsteamgeneratorscharacteristicsoflargetimedelayandmodeluncertainty.WealsogaveasimulationtothesteamgeneratorofQinshannuclearpowerplant,andachievedsatisfactoryresults.Themethodcanalsobeusedforotherlargetime-delayandtime-varyingprocesscontrolmodel,andhasbroadapplicationprospects.中文译文蒸汽发生器水位模糊控制研究托马斯索沃尔摘要蒸汽发生器是一个高度复杂、非线性、时变的非最小相位系统，由“收缩”与“膨胀”反动力效应引起的“虚假液位”现象使蒸汽发生器水位控制变得复杂。由于传统的PID控制器的参数难以实现在线整定，很难满足核动力装置瞬态情况下的自动控制要求。现代控制理论完全依赖于被控对象动态特性的精确数学模型，而模糊控制技术不依赖于被控对象的精确数学模型，且具有较强的适应对象参数变化的能力，适于蒸汽发生器水位的控制。1.导论蒸汽发生器是压水反应堆式核电厂里的一个重要的设备。为了保证核电厂运行的安全性，蒸汽发生器的水位必须控制在一定的范围内。核电厂的运行中，因为蒸汽流量和给水流量的改变，蒸汽发生器里沸水中的气泡数量会随着局部气压和温度的变化而改变，瞬时水位呈现“虚假液位”现象。正是由于“虚假液位”的存在使得水位控制变得困难。将前馈控制引入到传统的单回路PID控制中，可以在一定程度上克服“虚假液位”的问题。但是蒸汽发生器的传统PID控制仍然存在着一些不足。对于具有高度复杂，大滞后，非线性特征的蒸汽发生系统，不仅PID参数的调整单调乏味，控制效果也很差。并且当条件改变时，为了获得好的控制性能，通常需要改变PID控制器的参数，但是模拟量的PID控制器参数的在线调整是很难的。模糊控制是一种基于模糊推理的非线性的控制方法，它体现了熟练操作人员的实际经验和模糊语言推理的一般规则。模糊控制不需要知道被控对象的精确的数学模型，它对过程参数的变化并不敏感，鲁棒性很强，能够克服非线性因素，因此，模糊控制有更快的响应速度，更小的超调，更好的控制效果。基于以上了解，本文设计了一个蒸汽发生器水位的模糊控制器，仿真结果表明这个控制器有更好的控制效果和实用价值。2.蒸汽发生器的动态特性压水堆蒸汽发生器一般形式的数学模型的传递函数如下所示：()=()()+()()（1）其中，y代表蒸汽发生器的水位；QW代表给水流量；QS代表蒸汽流量；GW代表给水流量对蒸汽发生器水位的作用；GS代表蒸汽流量对蒸汽发生器的水位的作用。蒸汽发生器水位的平衡是靠蒸汽流量和给水流量的匹配来维持的。可以将水位随蒸汽流量或者给水流量变化而变化看作一个简单的一体化过程，蒸汽流量变化和给水流量变化对水位的影响又是不同的。1.给水流量扰动下的动态特性假设蒸汽流量保持不变，而给水流量阶跃增加，一方面，由于新增给水的温度要比蒸汽发生器中的饱和水的温度低很多，因此，当新水进入后就会吸收大量的额外热量，水中的气泡含量大大减少，从而导致水位下降；另一方面，给水流量大于蒸汽负荷，引起水位线性增加。综合以上两点，当给水阶跃增加，水位增长会有一个延迟的过程，表现为先下降后上升。2.蒸汽负荷扰动下的动态特性假设给水流量保持不变，蒸汽负荷阶跃增加，一方面，由于蒸汽流速比给水流速大，水位会下降；另一方面，随着蒸汽负荷的增加，内部蒸汽压力降低，液面的气泡容积增加，从而引起水位增加。综合以上两个因素，当蒸汽流量阶跃增加以后，水位下降会有一个延迟的过程，表现为先上升后下降。给水流量或者蒸汽流量阶跃减少对水位的影响与上述有相似的原理。综上所述，当给水流量或者蒸汽负荷变化，水位不会立即跟随变化，开始会出现一个相反的过程。这个现象就称为“虚假液位”现象。3.水位模糊控制器的设计传统PID控制器对于蒸汽发生器水位的控制效果不佳，存在“虚假液位”的现象，表现为跟踪设定值时有较大的超调。但是，一个设计合理的模糊控制器能够克服“虚假液位”的现象，有较好的控制效果。1.模糊控制器的结构模糊控制器的结构如图1所示。FuzzycontrollerK1valveGW(s)dx/dtK2GS(s)expectedwaterleverStreamflowWaterleverwaterfloweec+-+-+图1蒸汽发生器水位模糊控制器的结构选择水位偏差（e）和偏差变化率（ec）作为模糊控制器的输入，模糊控制器的输出量为阀门开度的增量信号u。同时，以蒸汽流量作为前馈信号来克服“虚假液位”现象，