Phasor Estimation Algorithm Based on Complex Frequency Filters for Digital Relaying

This paper presents a new filter-based algorithm to estimate the fundamental phasor of fault currents, using the proposed complex frequency filter. The presence of decaying dc component (ddc) in fault currents causes large error in discrete Fourier transform (DFT)-based phasor estimation methods. The proposed filter discriminates the ddc from dc and sinusoidal signals. In this algorithm, first, the ddc is filtered out by the proposed filter. Then, the fundamental phasor can be precisely extracted by applying DFT. Second and fourth order of the complex frequency filter and their design method are presented. To evaluate the performance of the proposed algorithm, several test signals are used. The algorithm is also compared with recent DFT-based and mimic-DFT methods, using four performance indices. The simulation results demonstrate the robustness of the proposed algorithm against harmonics, noise, multiple ddc components, and off-nominal frequency. It also offers faster convergence speed. The proposed complex frequency filter can also be used for the phasor estimation of harmonic components in the presence of ddc with no need to readjust its parameters.