Didviding and multiplying transfer functions

Question

Marko 2016-4-6

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/277481-didviding-and-multiplying-transfer-functions

评论： Syndi Katya 2024-2-21

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Hi all,

I have a question on transfer function division and multiplication. If I calculate the closed loop function using:

G/(1+G*H)

I obtain different results than if I try calculating it by hand or using command.

feedback(G,H)

For example

                4.244e-12 s^3 + 8.004e-08 s^2 + 8e-07 s
    ------------------------------------------------------------------------
    1.801e-19 s^5 + 6.792e-15 s^4 + 6.407e-11 s^3 + 4.308e-08 s^2 + 0.0008 s

This is the closed loop using first command. This is with feedback command:

             0.0001 s + 0.001
  -------------------------------------------
  4.244e-12 s^3 + 8.004e-08 s^2 + 8e-07 s + 1

While calculating it by hand gives:

               0.0001 s + 0.001
  -------------------------------------------
  4.244e-12 s^3 + 1.224e-07 s^2 + 8e-07 s + 1

Do you know how is this possible?

Thanks!

2 个评论
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J. Carlos Aguado 2020-10-7

You just have to apply "minreal" to your result, and you will see that minreal(G/(1+G*H)) = feedback(G, H). MatLab should you that automatically.

Syndi Katya 2024-2-21

Nice trick

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Answer 1

Debarati Banerjee 2016-4-12

4
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/277481-didviding-and-multiplying-transfer-functions#answer_217517

编辑：Debarati Banerjee 2016-4-12

Can you first apply the function ' minreal ' on your 'G' and 'H' functions before applying the closed loop formula? This 'minreal' function will reduce the systems into minimal order.

Also, can you please provide the G and H functions with which you arrived at these results?

Cheers!

Debarati