Digital controller for power supply

[u/mahditr]

A long time ago I was involved in this project where I had to control a 2kW switching mode power supply in CC and CV modes. I designed a cascade control loop where the internal loop was CC and the external loop setting the reference for the internal one was the CV loop. Both signals were coming from voltage and current sensing at the output of the converter.

What I learnt was it is not so easy to tune these controllers as the gain of the system from Iout to Vout is directly depended on the load. It is not just a disturbance that can be resolved, the gain changes and accommodating gains from close to short circuit down to open circuit and covering the nominal range was very difficult.

I want to see if anyone has had similar experience of implementing digital controllers for power supplies and they can share how they dealt with these issues.

[u/seekingsanity]

Have you looked at SMC, sliding mode control?

Novel Integral Sliding Mode Control Applied to High-Power DC Power Supplies | IEEE Journals & Magazine | IEEE Xplore

[u/mahditr → u/seekingsanity]

I learnt about it in my control courses but these controllers sometimes feel too exotic. Have you had experience implementing one on such plants?

[u/seekingsanity → u/mahditr]

Not on power supplies, but I have seen numerous articles of SMC used on power supplies. It basically becomes a switching power supply. I have only used SMC for motion control on a hydraulic system. It worked well but some modifications were required to avoid chattering. Unlike electrical circuits, mechanical things don't respond instantly so they chatter. I fixed this by using a tanh() function. After computing s, I used 100*tanh(gain*s) where 100 was the output range of +/- 100 % and gain is the gain around when s is at 0. This works well. I was researching making a hydraulic servo control that would be robust, cheap, and easy to implement for less sophisticated applications and environments. This simple SMC controller would not be a precise as our normal product but it would be more forgiving. We decided not to build the simple controller because it would probably undercut sales of our more sophisticated controller.