O. Vainio et Sj. Ovaska, DIGITAL FILTERING FOR ROBUST 50 60 HZ ZERO-CROSSING DETECTORS/, IEEE transactions on instrumentation and measurement, 45(2), 1996, pp. 426-430
An improved digital filtering method for line frequency zero-crossing
detectors is proposed, The multistage filter efficiently attenuates ha
rmonics, wide-band noise, commutation notches, and other impulsive dis
turbances without causing any phase shift on the primary sinusoidal wa
veform, Our novel signal-processing system is a cascade of a median fi
lter and an adaptive sinusoid predictor, followed by up-sampling and i
nterpolation, The three-point median filter effectively removes impuls
es, and the predictor provides wide-band noise attenuation while compe
nsating for delays in the other processing steps, The predictor adapts
to possible line frequency variations within the specified range by c
hanging the set of coefficients, based on an estimate of the instantan
eous line frequency, The adaptive approach allows the use of highly se
lective IIR bandpass predictors.