Auto-Tuning of DC-DC Buck Converters Through the Modified Relay Feedback Test

This paper presents the design and application of the modified relay feedback test (MRFT) auto-tuning method to the PID voltage-mode control of dc-dc buck converters. The proposed method, which also includes a set of tuning rules, does not require knowledge of the converter or load parameters, and produces a controller with near-optimal dynamic performance for virtually any dc-dc buck converter. The proposed MRFT auto-tuning also guarantees a specified phase margin. An important feature of the MRFT auto-tuning is that it is non-complex and thus practical, consisting of a simple test stage and a quick tuning stage. In the test stage oscillations are excited using the MRFT algorithm, and the frequency and amplitude of these oscillations are measured. In the tuning stage, these measurements are used with the pre-designed tuning rules to calculate PID controller parameters. The designed MRFT auto-tuning is evaluated experimentally by using it to auto-tune four different dc-dc buck converter designs, where in each case parameters of the converter are unknown to the auto-tuning algorithm. The experimental results show good performance of the MRFT auto-tuned controller in all cases. A mathematical proof that the MRFT auto-tuning guarantees a specified phase margin is also provided.