Non-parametric auto-tuning of PID controllers for DC-DC converters

Abstract

This chapter has presented the design and implementation of an auto-tuning based on the MRFT tuning method for the class of digitally controlled voltage-mode dc-dc buck converters. The presented auto-tuning is simple and consists of short test and tuning stages, and it guarantees stability through allowing the specification of the gain or phase margin - all without requiring any knowledge of the converter or load parameters. The chapter provides a theoretical background on the MRFT, as well as an explanation of how the test stage is adapted to dc-dc switching power converters. The derivation of optimal tuning rules for the class of digitally controlled voltage-mode dc-dc buck converters is also given in detail. Besides guaranteeing a specified gain margin, the tuning rules are also optimized for dynamic performance of the considered class of converters. It is shown through an experiment on a test converter that the MRFT auto-tuned controller performs closely to an optimized controller designed with full knowledge of the test converter's parameters. It is finally noted that even for dc-dc buck converter designs that have LC parameters outside the design range used in developing the tuning rules, the auto-tuning still guarantees a stable performance with the specified gain margin and through that provides an acceptable performance.