S-Function-使用及应用举例

高范强@IEE版权所有1S-Function使用及应用举例【说明】近来在论坛中很多朋友问及Simulink下的S-函数的编写及使用方法，在西安交大BBS上，hii_yzf网友发表了有关S-函数使用的文章，举例比较详尽，相信对关心S-函数的网友会有很大帮助。发信人:hii_yzf(叶子),信区:MathTools标题:S-FUNCTIONS的书写之一发信站:交通大学思源BBS站(MonApr1616:35:092001),站内信件S-FUNCTIONS的书写之一s-function也就是system-function的缩写。说得简单，s-function就是用MATLAB所提供的模型不能完全满足用户，而提供给用户自己编写程序来满足自己要求模型的接口。要了解s-function，必须了解以下知识：（1）directfeedthrough（2）dynamicallysizedinputs（3）settingsampletimesandoffsets[由于我也不知道怎么把上面三句话精确的翻译成中文，因此在此不加翻译，大家自己理解，也许更好]由于上面三部分的重要性，在此详细进行分析。一.directfeedthroughdirectfeedthrough意思是说系统的输出或可变采样时间是否受到输入的控制。大家清楚有的系统是受到输入控制如：y=k*u(u是输入，k是放大因子，y是输出）而有的系统输出是不受到输入影响，如：输出：y=xdx=ux表示状态二.dynamicallysizedinputs主要是给出：输入连续状态数目（size.NumContStates),离散状态数目（size.NumDiscStates),输出数目（size.NumOutputs),输入数目(size.NumInputs),DirectFeedthrough(size.DirFeedthrough)。三.settingsampletimesandoffsetssettingsmapletimesandoffsets主要设置采样时间MATLAB为了用户方便，已经书写了S-FUNCTIONS模板函数sfuntmpl.m。为了更好的写S-FUNCTIONS，大家来看一下，该函数sfuntmpl.m内容如下：（我通过在该内容加注释来说明,以$开头）function[sys,x0,str,ts]=sfuntmpl(t,x,u,flag)$输出变量就此四个，大家必须注意它的顺序。$输入变量可以为t,x,u,flag,p1,...,pn等，但是前面的四个变量不能变，特此说明。%SFUNTMPLGeneralM-fileS-functiontemplate高范强@IEE版权所有2%WithM-fileS-functions,youcandefineyouownordinarydifferential%equations(ODEs),discretesystemequations,and/orjustabout%anytypeofalgorithmtobeusedwithinaSimulinkblockdiagram.%$上面是其功能%ThegeneralformofanM-FileS-functionsyntaxis:%[SYS,X0,STR,TS]=SFUNC(T,X,U,FLAG,P1,...,Pn)%$调用格式%WhatisreturnedbySFUNCatagivenpointintime,T,dependsonthe%valueoftheFLAG,thecurrentstatevector,X,andthecurrent%inputvector,U.%%FLAGRESULTDESCRIPTION%-------------------------------------------------------%0[SIZES,X0,STR,TS]Initialization,returnsystemsizesinSYS,%initialstateinX0,stateorderingstrings%inSTR,andsampletimesinTS.$具体怎样实现，大家参看后面的函数mdlInitializeSizes%1DXReturncontinuousstatederivativesinSYS.%2DSUpdatediscretestatesSYS=X(n+1)%3YReturnoutputsinSYS.%4TNEXTReturnnexttimehitforvariablestepsample%timeinSYS.%5Reservedforfuture(rootfinding).%9[]Termination,performanycleanupSYS=[].%$参看后面相应函数%%Thestatevectors,XandX0consistsofcontinuousstatesfollowed%bydiscretestates.%%Optionalparameters,P1,...,PncanbeprovidedtotheS-functionand%usedduringanyFLAGoperation.%%WhenSFUNCiscalledwithFLAG=0,thefollowinginformation%shouldbereturned:%%SYS(1)=Numberofcontinuousstates.%SYS(2)=Numberofdiscretestates.%SYS(3)=Numberofoutputs.%SYS(4)=Numberofinputs.%AnyofthefirstfourelementsinSYScanbespecified%as-1indicatingthattheyaredynamicallysized.The高范强@IEE版权所有3%actuallengthforallotherflagswillbeequaltothe%lengthoftheinput,U.%SYS(5)=Reservedforrootfinding.Mustbezero.%SYS(6)=Directfeedthroughflag(1=yes,0=no).Thes-function%hasdirectfeedthroughifUisusedduringtheFLAG=3%call.Settingthisto0isakintomakingapromisethat%UwillnotbeusedduringFLAG=3.Ifyoubreakthepromise%thenunpredictableresultswilloccur.%SYS(7)=Numberofsampletimes.ThisisthenumberofrowsinTS.%$需要说明的是sys的顺序不能乱%%X0=Initialstateconditionsor[]ifnostates.%%STR=Stateorderingstringswhichisgenerallyspecifiedas[].%%TS=Anm-by-2matrixcontainingthesampletime%(period,offset)information.Wherem=numberofsample%times.Theorderingofthesampletimesmustbe:%%TS=[00,:Continuoussampletime.%01,:Continuous,butfixedinminorstep%sampletime.%PERIODOFFSET,:Discretesampletimewhere%PERIOD0&OFFSET〈PERIOD.%-20];:Variablestepdiscretesampletime%whereFLAG=4isusedtogettimeof%nexthit.%%Therecanbemorethanonesampletimeproviding%theyareorderedsuchthattheyaremonotonically%increasing.Onlytheneededsampletimesshouldbe%specifiedinTS.Whenspecifyingthanone%sampletime,youmustcheckforsamplehitsexplicitlyby%seeingif%abs(round((T-OFFSET)/PERIOD)-(T-OFFSET)/PERIOD)%iswithinaspecifiedtolerance,generally1e-8.This%toleranceisdependentuponyourmodel'ssamplingtimes%andsimulationtime.%%YoucanalsospecifythatthesampletimeoftheS-function%isinheritedfromthedrivingblock.Forfunctionswhich%changeduringminorsteps,thisisdoneby%specifyingSYS(7)=1andTS=[-10].Forfunctionswhich高范强@IEE版权所有4%areheldduringminorsteps,thisisdonebyspecifying%SYS(7)=1andTS=[-1-1].%Copyright(c)1990-1998byTheMathWorks,Inc.AllRightsReserved.%$Revision:1.12$%%ThefollowingoutlinesthegeneralstructureofanS-function.%switchflag,%%%%%%%%%%%%%%%%%%%Initialization%%%%%%%%%%%%%%%%%%%case0,[sys,x0,str,ts]=mdlInitializeSizes;$大家是不是觉得此函数名太长，当然可以根据自己的爱好加以改变，不过后面的相应改。%%%%%%%%%%%%%%%%Derivatives%%%%%%%%%%%%%%%%case1,sys=mdlDerivatives(t,x,u);%%%%%%%%%%%Update%%%%%%%%%%%case2,sys=mdlUpdate(t,x,u);%%%%%%%%%%%%Outputs%%%%%%%%%%%%case3,sys=mdlOutputs(t,x,u);%%%%%%%%%%%%%%%%%%%%%%%%GetTimeOfNextVarHit%%%%%%%%%%%%%%%%%%%%%%%%case4,sys=mdlGetTimeOfNextVarHit(t,x,u);%%%%%%%%%%%%%%Terminate%%%%%%%%%%%%%%case9,sys=mdlTerminate(t,x,u);%%%%%%%%%%%%%%%%%%%%%Unexpectedflags%%%%%%%%%%%%%%%%%%%%%otherwise,error(['Unhandledflag=',num2str(flag)]);end%endsfuntmpl%%==============================================================高范强@IEE版权所有5===============%mdlInitializeSizes%Returnthesizes,initialconditions,andsampletimesfortheS-function.%=============================================================================%function[sys,x0,str,ts]=md