Filter coefficient (N) in PID block?
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Robert
on 17 Feb 2013
Commented: Andre Elliot
on 15 May 2023
Good evening folks!
While tuning my quadrotor model in Matlab I found that the Matlab PID function had a Filter coefficient (N) term in the PID equation. However I have not encountered such a term in my typical PID programs. How would one implement this term into the PID equation and what would be some simple C code to add this term into the derivative? I tried generating C code from my model but got a lot of header and C program files with nothing close to simple.
My current PID code line in C is:
U2 = KP * phi_error + KI * phi_errorsum + KD * (PHI_RATE_desired-PHI_RATE);
Many Thanks, Robert
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Accepted Answer
Arkadiy Turevskiy
on 12 Mar 2013
The code would look like that.
FilterCoefficient = (Kd * u - Filter_DSTATE) * N;
y = (Kp * u + Integrator_DSTATE) + FilterCoefficient;
Integrator_DSTATE += Ki * u * 0.01;
Filter_DSTATE += 0.01 * FilterCoefficient;
HTH.
Arkadiy
4 Comments
Marzieh Hosseini
on 6 May 2021
Hi,
Is it the same code if I want to implement PID in Matlab code, while I am controlling a device directly with Matlab and I got real time information in my Matlab?
More Answers (3)
Shashank Prasanna
on 17 Feb 2013
Hi Robert, this link should give you a better idea of what N means:
If you have Simulink Control Design toolbox, then you can use the built in pidtune functionality to tune the PID.
1 Comment
Brian Candiloro
on 13 Jan 2023
Can this filter term be realized in a physical opamp differentiator circuit or only in code?
Robert
on 21 Feb 2013
1 Comment
Seng Tak Goh
on 11 Mar 2019
Hi Robert,
In essence, the filtered derivative is doing a first order filtering on the change of the inputs, scaled by D gain.
The 1/s integrates the previous output scaled by N term, then adding the input change scaled by D * N to produce the output.
If you multiply the D term of the continuous form by s, you will see it better how the filtering comes into play.
In discrete form:
y[n] = D*N*(u[n]-u[n-1]) + (1-N*Ts)*y[n-1];
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