Simplified Model Reference Tuning of PID Regulators of Digitally Controlled DC-DC Converters Based on Crossover Frequency Analysis

An autotuning technique of voltage-mode regulators for digitally controlled dc-dc converters, which is based on model reference approach, is proposed. The system is excited by a frequency component which equals the desired control bandwidth. The difference between the output of real system and the one of the reference model is used to set regulator parameters in order to obtain desired gain and phase margin at the crossover frequency. The procedure is firstly described for two-parameters controllers (proportional-integral (PI) or proportional derivative (PD) controller) and then extended to more general PID regulators. The latter is obtained either injecting an additional frequency component, or, alternatively, using a single frequency signal in a two step procedure. The proposed solution has the advantage of simplicity, good precision in presence of sampling noise, independence on the converter topology, and small signal processing requirement. Experimental investigation has been performed on a synchronous buck converter, and both simulation and experimental results confirm the effectiveness of the proposed solution.