S-Function 使用及应用举例.

如

:

输出

:y=x

dx=u

x

表示状态

二

.dynamically sized inputs < /p>

主要是给出

:

输入连续状态数目

(tStates,

离散状态数目

(cStat es

,

输出数目

(puts,

输入数目

(uts,Direct Feedthrough(

Feedthrough

。三

.setti ng sample times and offsets

setting smaple times and offsets

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

s funtmpl.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。

%SFUNTMPL General M-file S-function template

% With M-file S-functions, you can define you own ordinary differential %

equations (ODEs, discrete system equations, and/or just about

% any type of algorithm to be used within a Simulink block diagram.

%

$$

上面是其功能

% The general form of an M-File S-function syntax is:

% [SYS,X0,STR,TS] = SFUNC(T,X,U,FLAG,P1,...,Pn

%

$$

调用格式

% What is returned by SFUNC at a given point in time, T, depends on the % value

of the FLAG, the current state vector, X, and the current

% input vector, U.

%

% FLAG RESULT DESCRIPTION

% ----- ------ --------------------------------------------

% 0 [SIZES,X0,STR,TS] Initialization, return system sizes in SYS,

% initial state in X0, state ordering strings

% in STR, and sample times in TS.

$$

具体怎样实现

,

大家参看后面的函数

mdlInitializeSizes

% 1 DX Return continuous state derivatives in SYS.

% 2 DS Update discrete states SYS = X(n+1

% 3 Y Return outputs in SYS.

% 4 TNEXT Return next time hit for variable step sample

% time in SYS.

% 5 Reserved for future (root finding.

% 9 [] Termination, perform any cleanup SYS=[].

%

$$

参看后面相应函数

%

% The state vectors, X and X0 consists of continuous states followed

% by discrete states.

%

% Optional parameters, P1,...,Pn can be provided to the S-function and % used

during any FLAG operation.

%

% When SFUNC is called with FLAG = 0, the following information

% should be returned:

%

% SYS(1 = Number of continuous states.

% SYS(2 = Number of discrete states.

% SYS(3 = Number of outputs.

% SYS(4 = Number of inputs.

% Any of the first four elements in SYS can be specified

% as -1 indicating that they are dynamically sized. The

% actual length for all other flags will be equal to the

% length of the input, U.

% SYS(5 = Reserved for root finding. Must be zero.

% SYS(6 = Direct feedthrough flag (1=yes, 0=no. The s-function

% has direct feedthrough if U is used during the FLAG=3

% call. Setting this to 0 is akin to making a promise that

% U will not be used during FLAG=3. If you break the promise

% then unpredictable results will occur.

% SYS(7 = Number of sample times. This is the number of rows in TS. %

$$

需要说明的是

sys

的顺序 不能乱

%

% X0 = Initial state conditions or [] if no states.

%

% STR = State ordering strings which is generally specified as [].

%

% TS = An m-by-2 matrix containing the sample time

% (period, offset information. Where m = number of sample

% times. The ordering of the sample times must be:

%

% TS = [0 0, : Continuous sample time.

% 0 1, : Continuous, but fixed in minor step

% sample time.

% PERIOD OFFSET, : Discrete sample time where

% PERIOD > 0 & OFFSET

〈

PERIOD.

% -2 0]; : Variable step discrete sample time

% where FLAG=4 is used to get time of

% next hit.

%

% There can be more than one sample time providing

% they are ordered such that they are monotonically

% increasing. Only the needed sample times should be

% specified in TS. When specifying than one

% sample time, you must check for sample hits explicitly by

% seeing if

% abs(round((T-OFFSET/PERIOD - (T-OFFSET/PERIOD

% is within a specified tolerance, generally 1e-8. This

% tolerance is dependent upon your model's sampling times

% and simulation time.

%

% You can also specify that the sample time of the S-function

% is inherited from the driving block. For functions which

% change during minor steps, this is done by

% specifying SYS(7 = 1 and TS = [-1 0]. For functions which

% are held during minor steps, this is done by specifying

% SYS(7 = 1 and TS = [-1 -1].

% Copyright (c 1990-1998 by The MathWorks, Inc. All Rights Reserved.

% $$Revision: 1.12 $$

%

% The following outlines the general structure of an S-function.

%

switch flag,

%%%%%%%%%%%%%%%%%%

% Initialization %

%%%%%%%%%%%%%%%%%%

case 0,[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 %

%%%%%%%%%%%%%%%

case 1,sys=mdlDerivatives(t,x,u;

%%%%%%%%%%

% Update %

%%%%%%%%%%

case 2,sys=mdlUpdate(t,x,u;

%%%%%%%%%%%

% Outputs %

%%%%%%%%%%%

case 3,sys=mdlOutputs(t,x,u;

%%%%%%%%%%%%%%%%%%%%%%%

% GetTimeOfNextVarHit %

%%%%%%%%%%%%%%%%%%%%%%%

case 4,sys=mdlGetTimeOfNextVarHit(t,x,u;

%%%%%%%%%%%%%

% Terminate %

%%%%%%%%%%%%%

case 9,sys=mdlTerminate(t,x,u;

%%%%%%%%%%%%%%%%%%%%

% Unexpected flags %

%%%%%%%%%%%%%%%%%%%%

otherwise, error(['Unhandled flag = ',num2str(flag];

end

% end sfuntmpl

%

%================ ==========================================

< br>====

===============

% mdlInitializeSizes

% Return the sizes, initial conditions, and sample times for the S-function.

%========================== ================================

==== ===============

%

function [sys,x0,str,ts]=mdlInitializeSizes

%

% call simsizes for a sizes structure, fill it in and convert it to a

% sizes array.

%

% Note that in this example, the values are hard coded. This is not a

% recommended practice as the characteristics of the block are typically

% defined by the S-function parameters.

%

$$

关于函数

simsizes

大家必须遵循< /p>

,

因为把是内部函数

,

< br>不得随便改变

,

其作用是

返回未 初始化的

size

结构。

sizes = simsizes;

$$number of continuous states

tStates = 0;

$$number of discrete states

cStates = 0;

$$number of outputs

puts = 0;

$$ number of inputs

uts = 0;

$$Flag for direct feedthrough

dthrough = 1;

$$number of sample times

pleTimes = 1;

% at least one sample time is needed

$$

sys = simsizes(sizes;

%

% initialize the initial conditions

%

x0 = [];

%

% str is always an empty matrix

%

str = [];

%

% initialize the array of sample times

%

ts = [0 0];

% end mdlInitializeSizes

%

%========================== ================================

==== ===============

% mdlDerivatives

% Return the derivatives for the continuous states.

%=================== =======================================

==== ===============

%

function sys=mdlDerivatives(t,x,u

sys = []; % end mdlDerivatives

%

%========================= =================================

==== ===============

% mdlUpdate

% Handle discrete state updates, sample time hits, and major time step

% requirements.

%======================== ==================================

==== ===============

%

function sys=mdlUpdate(t,x,u

sys = []; % end mdlUpdate

%

%========================================= =================

==== ===============

% mdlOutputs

% Return the block outputs.

%======================= ===================================

==== ===============

%

function sys=mdlOutputs(t,x,u

sys = []; % end mdlOutputs

%

%============== ============================================

==== ===============

% mdlGetTimeOfNextVarHit

% Return the time of the next hit for this block. Note that the result is

% absolute time. Note that this function is only used when you specify a

% variable discrete-time sample time [-2 0] in the sample time array in

% mdlInitializeSizes.

%================== ========================================

==== ===============

%

function sys=mdlGetTimeOfNextVarHit(t,x,u

sampleTime = 1; % Example, set the next hit to be one second later.

sys = t + sampleTime; % end mdlGetTimeOfNextVarHit

%

%========================= =================================

==== ===============

% mdlTerminate

% Perform any end of simulation tasks.

%====================================== ====================

==== ===============

%

function sys=mdlTerminate(t,x,u

sys = []; % end mdlTerminate

在下面我将写几个具体的实例。

之二、连续系统例子

:

function [sys,x0,str,ts] = csfunc(t,x,u,flag

%CSFUNC An example M-file S-function for defining a continuous system.

% Example M-file S-function implementing continuous equations:

% x' = Ax + Bu

% y = Cx + Du

%

% See sfuntmpl.m for a general S-function template.

%

% See also SFUNTMPL.

% Copyright (c 1990-1998 by The MathWorks, Inc. All Rights Reserved.

% $$Revision: 1.5 $$

A=[-0.09 -0.01; 1 0];

B=[ 1 -7; 0 -2];

C=[ 0 2; 1 -5];

D=[-3 0; 1 0];

switch flag,

%%%%%%%%%%%%%%%%%%

% Initialization %

%%%%%%%%%%%%%%%%%%

case 0,[sys,x0,str,ts]=mdlInitializeSizes(A,B,C,D;

%%%%%%%%%%%%%%%

% Derivatives %

%%%%%%%%%%%%%%%

case 1,sys=mdlDerivatives(t,x,u,A,B,C,D;

%%%%%%%%%%%

% Outputs %

%%%%%%%%%%%

case 3,sys=mdlOutputs(t,x,u,A,B,C,D;

%%%%%%%%%%%%%%%%%%%

% Unhandled flags %

%%%%%%%%%%%%%%%%%%%

case { 2, 4, 9 },sys = [];

%%%%%%%%%%%%%%%%%%%%

% Unexpected flags %

%%%%%%%%%%%%%%%%%%%%

otherwise, error(['Unhandled flag = ',num2str(flag];

end

% end csfunc

%

%================== ========================================

==== ===============