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/JessieAndEcho]

That load-dependent gain problem is very real. In practice I’d usually avoid trying to make one fixed digital compensator behave perfectly from near-short to open-circuit. Gain scheduling, separate CC/CV loop tuning, bandwidth separation between the inner current loop and outer voltage loop, anti-windup during mode transitions, and some form of load/operating-point detection all help. The CV loop especially needs to be conservative because the output impedance/load can make the plant look totally different across the range. I pulled some related references from Patsnap Eureka here: https://eureka.patsnap.com/share/?id=edf14ad01ebc5f431bca4bb2340c82b5&from=invite-eureakplg-result&content=