求助matlab求传递函数问题

382709743

function f=m()
s=tf('s');G=12/(s*(s+1)^3).*exp(-2*s)
Gc=tf([2,3],[1,0],'Variable','s')
f=feedback(G,Gc)

??? Error using ==> exp
Function 'exp' is not defined for values of class 'tf'.

求G，Gc的单位负反馈函数。

yufeng

系统是通过tf编写的

ChaChing

LZ的版本是多少?
s=tf('s');G=12/(s*(s+1)^3).*exp(-2*s), 在R2006a & R2009a是不会报错的!

382709743

回复 3 # ChaChing 的帖子

我的是6.5的版本。。

zhouyang664

在R2008a上执行的结果：
%------------m.m----------------
function f=m()
s=tf('s');G=12/(s*(s+1)^3).*exp(-2*s)
Gc=tf([2,3],[1,0],'Variable','s')
f=feedback(G,Gc)
%---------------------------------
Transfer function:
                      12
exp(-2*s) * -----------------------
            s^4 + 3 s^3 + 3 s^2 + s


Transfer function:
2 s + 3
-------
   s

??? Error using ==> lti.feedback at 127
Error using ==> ltipack.tfdata.feedback at 20
System interconnection gives rise to internal
delays and can only be represented in state
space. Convert at least one of the models to
state space using the "ss" command.

Error in ==> Untitled at 4
f=feedback(G,Gc)

tenglang

没怎么研究过tf, 早期版本的tf 好象不能处理带有延时环节
tf 函数在Matlab 6.5 与 matlab 2009a  的help 中提到
in Matlab 6.5

1. You can then specify transfer functions directly as rational expressions
   
2.      in S or Z, e.g.,
   
3.         s = tf('s');  H = (s+1)/(s^2+3*s+1)

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in Matlab 2009

1. You can then specify transfer functions directly as expressions in S
   
2.      or Z, e.g.,
   
3.         s = tf('s');  H = exp(-s)*(s+1)/(s^2+3*s+1)

复制代码