A new method for instantaneous power system frequency measurement using reference points detection

An accurate power system frequency measurement is difficult due to the presence of unwanted noise including higher-order harmonics, de component and random noise. An algorithm that creates unique reference points in a sinusoidal signal corrupted by unwanted noise is introduced in this paper and used for precise instantaneous frequency measurement. The reference points are determined using symmetry features of the power signal. They are used to measure time between each two consecutive cycles and further to determine signal frequency. The algorithm that determines reference points employs two main features important for precise frequency measurement: a 'correlation' feature to remove the random noise effect, and a modified 'symmetry detection' feature to generate a single reference point at a unique location (time instance) in each cycle. The method is aimed at frequency relays for load shedding application. (C) 2000 Elsevier Science S.A. All rights reserved.