Adaptive lowpass filters for zero-crossing detectors

Computationally efficient adaptive digital filters are introduced for 50/60 Hz line frequency signal processing in zero-crossing detectors in power converters. The purpose of the filter is to extract the fundamental sinusoidal signal from noise and impulsive disturbances so that the output is accurately in phase with the primary input signal. The proposed filters have fixed coefficients which are multiplied by adaptive parameters in order to adapt to the instantaneous line frequency. Only two adaptive parameters are needed in this method. Two linear-phase approaches are considered for the basis filters, one designed for good stopband attenuation and the other for computational simplicity.