Sample correction for digitally controlled boost PFC converters operating in both CCM and DCM

Abstract

PFC converters for the higher power range are commonly designed for continuous conduction mode. Nevertheless, at light load, DCM will appear close to the crossover of the line voltage, causing the converter to switch between CCM and DCM. As a result of this switching during a line period, the converter dynamics change abruptly, yielding input current distortion. Moreover, if digital control is applied, another source of input current distortion is posed by the sampling algorithm. After all, the sampling algorithm is only designed to produce samples of the averaged input current in CCM. In this paper, after a study of the input current distortion caused by the sampling algorithm, a correction factor is derived to compensate for the error on the input current samples. The theoretical results are verified experimentally by using a digitally controlled boost PFC converter.