Study on the DFT-based phasor estimation algorithm for removal of the decaying DC offset

Abstract

Protection relays respond to the fault condition of power system using real-time voltage and current signals. Estimation of the voltage and current phasors is necessary. However, the decaying DC component contained in the signal causes overshoot and oscillations in the magnitude and angle of the phasor estimated by the traditional DFT algorithm. Two types of estimation algorithms removing effect of the decaying DC component are studied and compared in this paper. The two improved algorithms include an error estimation (EE) algorithm featured with estimating the decaying DC component characteristics and a differential DFT (DD) algorithm featured with prefiltering of the current signal prior to phasor estimation. Performance of the two algorithms is evaluated using simulated signals from Matlab and PSCAD software. Accuracy of the phasor estimation is improved and the DD algorithm has more excellent performance than the EE algorithm.