Auto-Tuning of PID Controller with Gain Margin Specification for Digital Voltage-Mode Buck Converter

Abstract

This paper investigates application of an auto-tuning of a digital PID controller for a DC-DC buck converter, based on the modified relay feedback test (MRFT). Amplitude and frequency of the MRFT oscillations are used as input to PID controller tuning rules that are proposed in this paper. These rules are coordinated with the MRFT through a certain parameter in order to allow for the specification of gain margin - for which a mathematical proof is provided in the paper. Another contribution of this work is the development of the implementation of the MRFT auto-tuning method on a digitally-controlled DC-DC buck converter. A PID controller is auto-tuned and tested on a digitally-controlled buck converter prototype, and its performance is compared to that of an optimal but non-auto-tunable controller. Results show good performance of the proposed method. A final contribution is the discussion of important practical considerations regarding the application of the MRFT-based auto-tuning to switching converters.