Adaptive measurement of power system currents, voltages and impedances in off-nominal frequency conditions

The problem of basic power system electric quantities (current, voltage magnitudes, power and impedance) measurement in off-nominal frequency conditions is considered under the assumption that the quantities are calculated from orthogonal components of input current and voltage phasors which are obtained by the use of nonrecursive digital filters. Adaptive algorithms which make the measurement insensitive to wide range frequency changes of the input signals are presented. The adaptive features of the algorithms are obtained by use of the frequency measuring algorithm and modification of orthogonal filter coefficients and data window length. Sample results of simulation studies which show the algorithm performance are presented and discussed