Self-tuning digital comb filter for PFC applications

Design and implementation of a self-tuning digital comb filter for power factor correction (PFC) rectifier applications are described. The comb filter enables fast response to load transients in universal input rectifiers and consequently more optimal design of the PFC power stage and a downstream DC/DC converter. The design is based on a modification of a conventional comb filter and implementation of frequency selector logic. The filter is used to eliminate the second and higher harmonic components from the voltage loop, while the frequency selector logic provides automatic adjustments of the filter characteristics and correct operation for different input line frequencies. Experimental results obtained on a 200 W universal-input boost PFC prototype are demonstrated.