What does N represent in the PID formula (see image copied from the compensator tuning function)?

Answer 1

[Vidya Sagar Reddy Kurre]

Hello Oren,

N is Filter Coefficient.

Regards!

[Oren Eliezer]

Hello Vidya,

Thank you for the quick repsonse.

I still don't understand what filer coefficient that is. Where is the filtering applied and what type of filtering?

Thanks again,

Oren

[Vidya Sagar Reddy Kurre]

Hello Oren,

The derivative gain of the PID controller is never implemented as pure cause it would be extremely sensitive for noise. To avoid the noise, Filter Coefficient is added to the Derivative. It is kept to minimum, and is called low-pass filter. More explanation on this can be found in the following links

https://youtu.be/7dUVdrs1e18

https://youtu.be/sFOEsA0Irjs

Hope this is helpful. Regards!

[Oren Eliezer]

Thanks Vidya! This is very helpful!

[Vidya Sagar Reddy Kurre]

Hello Oren,

Hope you accept the answer! And it provided better understanding on the concept.

Thank You! Regards.

[Oren Eliezer]

Hello Vidya,

Yes, thanks. I was confused since the "N" appeared like some integer, but after watching the video you suggested, I understood that this is just some coeficient like "a", represeting a pole (low-pass filtering to supress high frequencies) and it does not represent an integer.

My interest is in the context of a PID controller for a switched-mode power supply (i.e. voltage ragulation based on PWM), where it is customeray to have such pole in the feedback path (what Brian calls "sensor" in his video), but is the intent here that the filtering is only in the derivative path of the PID? I don't see a diagram.

Thanks again,

Oren

[Vidya Sagar Reddy Kurre]

Hello Oren,

The below image might help you understand the Filter application.

The same is explained at 09:38 duration in the first video link.

Thank You!! Regards.

[Oren Eliezer]

Hello Vidya,

Ok, now I understand the structure. So the presence of this filter seems to be the defualt strcuture for the PID controller assumed in Simulink. In my application this is a discrete-time PID compensator for which no such filtering is in the D path. However, there is an analog low-pass filter in the output sensing, which gives an equivalent effect (doesn't matter much that it also acts on the signal that is also fed into the P and I branches). Now I noticed that there is a selection "use filtered derivative", which I can simply unselect to reduce the D path to simple derivative.

Thanks again,

Oren