PID implementation using code

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Sanjeet Kulkarni
Sanjeet Kulkarni on 24 Nov 2022
Commented: Sanjeet Kulkarni on 28 Nov 2022
I have implemented a PID controller using simulink pid block for a system. I was trying to implement the same thing using a PID code (formula) in a matlab function block and compare the performances. However, I am getting differences in both the cases. Unable to figure out where exactly is the problem.
For simulink block I have implemented antiwindup, similarly I have done it in the code.
PID code as in the matlab function is as below:
function y = fcn(error,kp,ki)
dt = sampletime;
persistent integral newintegral
if isempty(integral)
integral = 0;
end
if isempty(newintegral)
newintegral = 0;
end
newintegral = integral + (error*dt);
output = kp*error + ki * integral;
if output>48000
output=48000;
elseif output<3000
output =3000;
else
integral = newintegral;
end
y = output;
Is there anything that I am implementing wrong in the code? Requesting some help/direction.
Thank you

Answers (1)

Sam Chak
Sam Chak on 25 Nov 2022
Wouldn't it be simpler if you obtain the signal directly from the Integrator block, and then feed it into the MATLAB function block? Something like this
function y = fcn(err, errint, Kp, Ki)
where err is the error signal and errint is the intergral of error signal.
  3 Comments
Sanjeet Kulkarni
Sanjeet Kulkarni on 28 Nov 2022
I have used the clamp method of antiwindup, where in the integral action should be clamped to the maximum and mininum limits of the actuator.
Have declared integral as a persistent variable (not the built in function).

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