Comparison of Relay Feedback Tuning and Other Tuning Methods for a Digitally Controlled Buck Converter

This paper presents a comparison between relay feedback tuning and other controller tuning methods for a digitally controlled DC-DC buck converter operating in continuous conduction mode. In the first method, a relay feedback test is used to obtain ultimate gain and period measurements experimentally. PI and PID controllers are then tuned according to the classic Ziegler-Nichols formulae. In the second and third method, a converter model is developed based on experimental identification and analytical derivation, respectively. PI and PID controllers are then designed through optimization of an integral performance criterion applied to the simulated step response. Experimental tests show that all three approaches to controller tuning provide comparable and acceptable results, but the simplicity of the approach based on the relay feedback test makes it a viable alternative to offline-tuned optimal controllers given the ability of the former to retune the controller to adapt to system changes. Results also suggest that with some improvements to the test and tuning rules, a well-tuned controller may be produced with reasonable computational effort in the auto-tuning schema.