Current PI Autotuning

[Candas1]

Shared by @mcells from his fork https://github.com/mcells/Arduino-FOC/blob/d40c7d7fddff4c3e58b26ebd2e2cc846fddfc09e/src/HFIBLDCMotor.cpp#L71

if phase resistance and phase inductance are known:

Will initialize Kp and Ki for q and d current PI controllers automatically based on phase resistance, phase inductance and current bandwidth (default 300).
Needs to be adapted if Ld and Lq are available in the future.
⚠️ What if users have set phase resistance and phase inductance but were using default PI parameters ? Is there an impact ?

if phase resistance and phase inductance are not known:

Same SimpleFOC default values as before are used.

Users that have already tuned their PIs:

They will overwrite Kp and Ki from their code.

[mcells]

Great!
One thing though, that part of the code is not by me, all credit goes to @Copper280z. I just had my fork on hand quicker when sharing this earlier🙈
Thanks for the mention regardless!

[Copper280z]

To be clear, this method is really more like pole placement, rather than autotuning.

I would recommend also setting the filter cutoff based on the controller bandwidth, otherwise the controller will have a higher bandwidth than the filter likely leading to some integral windup or something else undesirable happening. The default filter for faster chips has a cutoff frequency of ~30hz. Something like 1.5-5x the controller bandwidth (so 450-1500hz) is probably a good place to start. In the hfi fork we've been using a fixed ~2khz lowpass for both controllers.

[askuric]

Oohh, very very very nice!
Do you guys have some refereces/papers about this?

[Candas1]

Some time ago I shared this:
https://community.simplefoc.com/t/measuring-the-resistance-of-the-motor/3647/11?u=candas1

The blog and video in the the next post are great.

[askuric]

Nice, I'll look into it.

[Copper280z]

Oohh, very very very nice! Do you guys have some refereces/papers about this?

I believe I used a combination of this Ben Katz blog post and Elwin's project when I wrote this. I did some algebra to convert the coefficients to the form used in SFOC.
https://build-its-inprogress.blogspot.com/2016/08/desktop-inverted-pendulum-part-2-control.html

Extra fun fact is that this same method applies to tuning the velocity PI controller too! The units just change. I'd need to work it out though as I don't remember off the top of my head.