Transfer Function with one 1/s term

Question

Joseph Lorentsen 2020-8-6

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/575848-transfer-function-with-one-1-s-term

评论： Joseph Lorentsen 2020-8-6

I would like to represent a transfer function on MATLAB which includes one 1/s term, while the rest of the terms are 0 or positive exponent. Something like:

F=(1/s + s)/(s^2 + s +1).

The tf function can create a transfer function with all 0 or positive exponents, or one with all 0 and negative exponents, but not one which mixes them (as far as I can tell).

Does anyone know a way to represent such a transfer function in MATLAB?

If it helps, I'm hoping to use it with the nyquist function.

Thanks!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Sulaymon Eshkabilov 2020-8-6

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/575848-transfer-function-with-one-1-s-term#answer_475771

在 MATLAB Online 中打开

Hi,

It is straightforward:

T = tf([1 0 1], [1 1 1 0]); 
nyquist(T)

3 个评论
显示 1更早的评论隐藏 1更早的评论

Les Beckham 2020-8-6

It is the same thing. Multiply the numerator and denominator by 1/s and you will see that it is the same. The control system toolbox doesn't like negative exponents. So, don't try to force it to use them.

Joseph Lorentsen 2020-8-6

Good point, I guess that's true. Thanks!

请先登录，再进行评论。

Answer 2

Walter Roberson 2020-8-6

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/575848-transfer-function-with-one-1-s-term#answer_475801

You cannot do that with Control System Toolbox tf() function. tf() keeps numeric vectors of coefficients with implied powers; it does not store the powers explicitly and so cannot know that you want to use power of -1 . When you use calculations that might result in negative powers, it normalizes to a ratio of polynomials (each of which uses only positive powers.)

You can use the Symbolic Toolbox for your purpose of creating an object that will display that particular way. However, nyquist() does not accept symbolic objects, so you would have to code your own symbolic nyquist plot.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Joseph Lorentsen 2020-8-6

Ok. So I'm thinking, then, that the easiest solution will be to just enter in the tf multiplied by s on top and bottom, since I don't particularly care about the display of the transfer function (just the Nyquist plot). Thanks!

请先登录，再进行评论。