ESR Zero Estimation and Auto-compensation in Digitally Controlled Buck Converters

A method for estimating and compensating the zero introduced by the capacitor equivalent series resistance (ESR) in the buck converter transfer function is introduced. The method is well-suited for practical implementation with digital controllers. The ESR zero is estimated by online measurement of the output voltage ripple and the power stage corner frequency. Accordingly, the coefficients of the PID compensator are updated to avoid potential stability problems. Theoretical basis of the identification and the compensator design are presented. The method is experimentally verified on a 12 V-to-1.5 V, 500 kHz, 10 W buck converter prototype.