Fitting transfer function to amplitude phase data

Question

Hari 2015-3-17

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/183609-fitting-transfer-function-to-amplitude-phase-data

评论： Star Strider 2015-3-17

Hello,

I have amplitude-phase (Bode) data from my experiment, which I have obtained by sweeping a range of frequencies. My system has the delay term exp(-Tau*s). I am looking to fit transfer function models of the form exp(-Tau*s)*(N(s)/(D(s)) to my data with the lowest possible order. Any help would be greatly appreciated!

Thanks and Regards, Hari

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

Star Strider 2015-3-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/183609-fitting-transfer-function-to-amplitude-phase-data#answer_171672

You are fitting a matrix (amplitude and phase) with your model, so the most appropriate function to use is the Optimization Toolbox function lsqcurvefit. Your objective function will have to produce two outputs (amplitude and phase) to match your data.

2 个评论
显示无隐藏无

Hari 2015-3-17

Hi Star Strider, Thanks for your answer. I will look into this.

Star Strider 2015-3-17

My pleasure.

I hope it works for you.

请先登录，再进行评论。

Answer 2

Arkadiy Turevskiy 2015-3-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/183609-fitting-transfer-function-to-amplitude-phase-data#answer_171706

编辑：Arkadiy Turevskiy 2015-3-17

在 MATLAB Online 中打开

Actually the function specifically created for this task is tfest from System Identification Toolbox. Take a look at the doc page and look at the section "Examples". For the lowest possible order, specify the number of poles =1, and number of zeros =0. If you do not get a good fit, try to increase the number of poles and zeros.

tfest takes your data as an input argument. Data has to be in the idfrd format. You will need to convert your mag-phase data to complex-valued response with something like this:

>>response=mag.*exp(i*phase);

2 个评论
显示无隐藏无

Hari 2015-3-17

编辑：Hari 2015-3-17

Thanks for your answer. I have tried 'tfest' by taking known transfer function models. But tfest really struggles to fit when the order is higher with big polynomial coeffiecients. I am expecting an order of 10 with big polynomial coeffiecients .

I tried 'fitfrd' which is slightly better, but still has problems at higher orders.

Hari 2015-3-17