Frequency adaptive digital filter for synchronization signal aquisition and synchronized event triggering

This paper shows that a digital filter consisting of a variable sample rate cascaded median, bandpass and predictor filter is able to provide a zero degree phase shift error between the input and output of a time varying fundamental frequency. The phase shift error is marginally affected by typical disturbances found on a utility or stand-alone network. This filter can be used in a wide range of applications in which synchronization signals or synchronized event triggering signals are required such as synchronous gating signal-generators and discrete Fourier transforms. The frequency adaptive properties and magnitude versus frequency response of a variable sample rate cascaded third order median filter, 25th order Blackman filter and 15th order predictor filter have been experimentally verified. The output response of this filter when subjected to a wide range of line disturbances has also been simulated and exhibits acceptable characteristics