Frequency tracking in power networks in the presence of harmonics

Three new techniques for frequency measurement are proposed. The first is a modified zero-crossing method using curve fitting of voltage samples. The second method is based on polynomial fitting of the discrete Fourier transform (DFT) quasi-stationary phasor data for calculation of the rate of change of the positive sequence phase angle. The third method operates on a complex signal obtained by the standard technique of quadrature demodulation. All three methods are characterized by immunity to reasonable amounts of noise and harmonics in power systems. The performance of the proposed techniques is illustrated for several scenarios by computer simulation.>