PID controller, difference when graphing step function with PID control block in matlab and simulink

Question

hoang 2024-7-2，2:55

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评论： Sam Chak 2024-7-3，6:03

采纳的回答： Sam Chak

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Hi everyone,

please tell me, why is there a difference when graphing step function with PID control block in matlab and simulink

s =tf('s');
g = 1.883e5/(s*(s^2+4466*s+6.43e6));
kp = 60;
ki = 63000;
kd = 3;
gpid = pid(kp,ki,kd);
gsys = feedback(g*gpid,1);
step(gsys)

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Answer 1

Sam Chak 2024-7-2，4:16

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Hi @hoang

Both responses look similar if you implement them correctly as shown.

s = tf('s');

Gp = 1.883e5/(s^2 + 4466*s + 6.43e6);

kp = 60;

ki = 63000;

kd = 3;

Gc = pid(kp, ki, kd);

Gcl = feedback(Gc*Gp, 1);

step(Gcl), grid on, ylim([-0.1, 1.1])

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hoang 2024-7-3，2:13

Thanks for the repply @Sam Chak. It really helped.

Sam Chak 2024-7-3，6:03

Hi @hoang

I'm glad to hear that. If you find the explanation and code helpful, please consider clicking 'Accept' ✔️ on my Answer. Additionally, you can show your appreciation by voting 👍 for other answers by Paul and Umar as a token of support for their knowledge sharing. Your support is greatly appreciated!

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Answer 2

Paul 2024-7-2，3:28

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Hi hoang,

The posted code doesn't result in the same figure as in the question

s =tf('s');

g = 1.883e5/(s*(s^2+4466*s+6.43e6))

g = 188300 -------------------------- s^3 + 4466 s^2 + 6.43e06 s Continuous-time transfer function.

kp = 60;

ki = 63000;

kd = 3;

gpid = pid(kp,ki,kd);

gsys = feedback(g*gpid,1);

step(gsys)

Note also that g in the Matlab code has an integrator in the denominator that is not present in the plant model in the Simulink diagram.

What is inside the subsystem block in the Simulink diaggram?

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Umar 2024-7-2，3:51

I do agree with Paul’s suggestion.

hoang 2024-7-2，6:56

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I'm sorry I copied it wrong

g = 1.883e5/(s^2+4466*s+6.43e6);

My inside the subsystem block

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Answer 3

Umar 2024-7-2，3:00

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Hi Hoang,

My suggestion would be tuning the PID controller gains appropriately. You can use tools like the PID Tuner in Simulink or MATLAB's Control System Toolbox to adjust the controller parameters for better system performance. Try using the pidtune function to tune the PID controller. For more information regarding this function, please refer to

https://www.mathworks.com/help/control/ref/dynamicsystem.pidtune.html

Let me know if you need further assistance.