A synchronous digital filter for 50 Hz line frequency signal processing

A new multistage digital filter is proposed for 50 Hz line frequency signal processing in zero-crossing detectors and synchronous power systems. 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. This is accomplished with a cascade of a median filter, a linear-phase FIR filter and a phase corrector. A 10 kHz output timing resolution is achieved by up-sampling with a customized interpolation filter.