Autotuning of digitally controlled buck converters based on relay feedback

This paper proposes a simple autotuning technique for digitally controlled dc-dc synchronous buck converters. The proposed approach is based on the relay feedback method and introduces perturbations on the output voltage during converter soft-start. By using an iterative procedure, the tuning of PID parameters is obtained directly by including the controller in the relay feedback and by adjusting the controller parameters based on the specified phase margin and control loop bandwidth. A nice property of the proposed solution is that output voltage perturbations are introduced while maintaining the closed-loop control of the digitally controlled converters. The proposed algorithm is simple, requires small tuning times and it is compliant with the cost/complexity constraint of integrated digital ICs. Experimental investigation has been performed using discrete components, implementing the digital control in a field programmable gate array (FPGA). Simulation and experimental results of a 1.5 V-5 A synchronous buck converter confirm the effectiveness of the proposed solution