Can I trust this closed loop response and include it as a final result in my Thesis?

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Ayesha 2024-2-26

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评论： Sam Chak 2024-3-11

have obtained the open loop response of my real plant and then I identified the transfer function from that response which is shown as: The image shows a blue line of my identified plant transfer.

Now I have designed the controller for my plant, and took closed loop response using Simulink:

Does it seem to be the correct closed-loop response of my plant? I took the above response as follows,

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Answer 1

Sam Chak 2024-2-26

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Hi @Ayesha,

You can actually verify the result (from Check Bode Characteristics block) with the Bode plot of the Closed-loop System obtained in MATLAB.

%% Plant

Gp = tf(1, [1 1 1])

Gp = 1 ----------- s^2 + s + 1 Continuous-time transfer function.

%% PID Controller

Gc = pidtune(Gp, 'PIDF')

Gc = 1 s Kp + Ki * --- + Kd * -------- s Tf*s+1 with Kp = 2.09, Ki = 1.19, Kd = 0.91, Tf = 0.00549 Continuous-time PIDF controller in parallel form.

%% Closed-loop system

Gcl = feedback(Gc*Gp, 1)

Gcl = 167.8 s^2 + 381.4 s + 216.7 --------------------------------------------- s^4 + 183.1 s^3 + 350.9 s^2 + 563.5 s + 216.7 Continuous-time transfer function.

%% Bode plot of the frequency response of Gcl

bode(Gcl), grid oo

Bode plot obtained in Simulink:

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Ayesha 2024-3-11

@Sam Chak do you have answer for this issue?

https://www.reddit.com/r/ControlTheory/comments/1bb9p93/why_does_adding_a_feedforward_controller_decrease/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

Sam Chak 2024-3-11

Hi @Ayesha,

Unfortunately, I don't have a satisfactory answer. Could you please provide the theoretical proof to demonstrate that adding a feedforward MPC controller will increase the closed-loop bandwidth? This would allow individuals skilled in mathematics to investigate what might have deviated from your expectations.

Alternatively, it might be wise to post your problem on the MATLAB Answers forum, including the MATLAB code and Simulink model. This way, someone with expertise in MPC might be able to provide an answer.

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