Transfer function in Simulink different from Matlab

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Daniel P 2012-11-20

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采纳的回答： Pedro Villena

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Hey everybody,

I am plotting the step response of a transfer function with matlab and the result is fine.

Gs = (1/s^2) * (1 - 2*exp(-s*0.5) + exp(-s))

Result: http://up.picr.de/12549059jw.jpg

Now I am trying to build this function in Simulink with standard blocks, but the step response is different from matlab:

Model: http://up.picr.de/12549080vj.jpg

and

Result: http://up.picr.de/12549087ia.jpg

I have tried many different solver settings but the result is always the same. I anyone has Ideas what might be the problem, please let me know.

Thanks in advance,

Daniel.

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Azzi Abdelmalek 2012-11-21

What version of matlab are you using? this did'nt work for me

Daniel P 2012-11-21

Version R2012a

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Pedro Villena 2012-11-21

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编辑：Pedro Villena 2012-11-21

Gs = (1/s^2) * (1 - 2*exp(-s*0.5) + exp(-s))

Gs = 1/s^2 - (2/s^2)*exp(-s*0.5) + (1/s^2)*exp(-s)

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Daniel P 2012-11-21

I will try that later. Thanks for your effort.

Daniel P 2012-11-21

That looks good. It seem to work for the moment. Thank you very much.

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Ryan G 2012-11-20

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The easiest way to achieve the desired results would be with the LTI System block which comes with the Control System Toolbox. This allows you to create a system in MATALB and directly utilize it in Simulink.

However, your model as shown works. You need to adjust the relative tolerance in the configuration parameters to be tighter. Try 1e-6 or 1e-8 and check the results.