An improved digital filtering method for line frequency zerocrossing detectors is proposed. The multistage filter efficientlyattenuates harmonics, wide-band noise, commutation notches, and otherimpulsive disturbances without causing any phase shift on the primarysinusoidal waveform. Our novel signal processing system is a cascade ofa median filter and an adaptive sinusoid predictor, followed byup-sampling and interpolation. The three-point median filter effectivelyremoves impulses, and the predictor provides wide-band noise attenuationwhile compensating for delays in the other processing steps. Thepredictor adapts to possible line frequency variations within thespecified range by changing the set of coefficients, based on anestimate of the instantaneous line frequency. The adaptive approachallows the use of highly selective IIR bandpass predictors
展开▼
