Z transfer fcn under simulink and cmd line

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Bruce 2023-4-5

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1941954-z-transfer-fcn-under-simulink-and-cmd-line

评论： Jon 2023-4-6

采纳的回答： Jon

I create a simple cmd from S to Z domain as below, and the result is matched with my understanding；

clear

rth1=0.0268;

tau1=1066.6;

Ts=0.05;

tf1=tf(rth1,[tau1 1])

dtf1=c2d(tf1,Ts)

figure;

step(tf1);

figure

step(dtf1);

but when i create this under simulink, the result is not matched, as you can see the Z transfer fcn output is quite different with the S transfer fcn.

Is there anyone can help me?

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Jon 2023-4-5

Please attach you Simulink model and any scripts or other functions needed to run your example - thanks

Jon 2023-4-5

Please see my answer below, I was able to work out what the issue was without your code, so no need to attach it now

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采纳的回答

Jon 2023-4-5

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This appears to be due to a round off error in the denominator of the discrete transfer function input to Simulink.

Try for example with the denominator set to

[1 -0.999949]

instead of

[1 -1]

and you will see that the step response of the continuous and discrete approximation are now much closer

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Bruce 2023-4-6

Thanks a lot, Jon. Your answer and explaination is quite clear, thanks again!

Jon 2023-4-6

Your welcome, it was an interesting problem

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