On-line recursive method of phasor and frequency estimation for power system monitoring and relaying

A real-time method of phasor and frequency estimation is proposed in this study. The method is based on the recently developed signal processing tool, S-transform. It is implemented recursively by taking advantage of recursive complex band pass infinite impulse response filters with a low computational burden, using only 10 samples of the previous output and nine samples of the input signal. The method is implemented in the Matlab software and its performance is appraised considering the decaying DC component, noise and severe harmonic and inter-harmonic distortions and dynamic conditions. Moreover, a wavelet based method, a discrete Fourier and a recursive discrete Fourier based method for phasor estimation have been implemented and the performances of the methods have been compared in various operating conditions. To assess methods performances for real signals, the recorded signals of a differential relay have been fed to all of the methods and their performances compared. In addition, a power system has been simulated in the EMTP software, and performances of the methods have been assessed using the recorded fault signals of the EMTP software. Both the real data and simulation results indicate that the proposed S-transform based method is superior to other methods considering dynamic and static conditions.