Phase measurement of distorted periodic signals based on nonsynchronous digital filtering

Measurement of the phase angle between fundamental components of distorted periodic signals at power frequencies is described. It is based on a nonsynchronous multirate digital filtering algorithm, which is applied to the voltage and/or current signals to be measured. The digital filters implemented are designed to suppress the higher harmonics and ensure the accuracy of measurement. The measurement method is insensitive to frequency variations in a wide frequency band around the nominal frequency. For a frequency band of /spl plusmn/10% around the nominal frequency, this method can resolve phase differences of less than 5 /spl mu/rad with an uncertainty of less than /spl plusmn/25 /spl mu/rad.