Discrepancy between MATLAB and Simulink closed loop response?

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Ryan Rizzo 2019-1-7

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https://ww2.mathworks.cn/matlabcentral/answers/438685-discrepancy-between-matlab-and-simulink-closed-loop-response

评论： Ryan Rizzo 2019-1-7

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I have a closed loop system which I am testing in MALTAB and Simulink, expecting the same output.

**MATLAB**

    num_plant = [0.0001 10];
    den_plant = [0.005 5 0.6616 61.01 2.11 20];
    G1 = tf(num_plant, den_plant)
    
    num_controller = [46615 6526 5.722e05 2.389e04 2.001e05]
    den_controller = [1 404 41605 162000 200000]
    
    C2 = tf(num_controller, den_controller)
    G2=G1*C2; %G1 is same 5th order TF as Simulink
    new2 = feedback(G2, 1);
    step(new2)

Note:

    G1 =
     
                           0.0001 s + 10
      --------------------------------------------------------
      0.005 s^5 + 5 s^4 + 0.6616 s^3 + 61.01 s^2 + 2.11 s + 20
    C2 =
     
      46615 s^4 + 6526 s^3 + 572200 s^2 + 23890 s + 200100
      ----------------------------------------------------
         s^4 + 404 s^3 + 41605 s^2 + 162000 s + 200000

**SIMULINK**

----------

According to the official documentation, feedback should be doing what I am presenting with blocks in Simulink. Surely I am missing something. I checked the code and everything should be the same in both cases. What is the reason for this discrepancy?

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Aquatris 2019-1-7

What version of Matlab are you using?

I used the script (coppied your code without change other than adding grid on) in Matlab 2013a and the result looks identical to your simulink results.

Ryan Rizzo 2019-1-7

Thanks for trying this out! I am using MATLAB R2018a. I cannot understand why our results differ so much! Any suggestions on what I should do? Could it be that I'm using a different solver or something of the sort?

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