A DFT-based phasor estimation method robust to primary and secondary decaying DC components

Abstract

Fault current signals typically suffer from primary and secondary decaying DC (DDC) components due to the transient response of the power system and current transformer. On the other hand, the conventional phasor estimation method, discrete Fourier transform (DFT), is severely sensitive to these components and exhibits a significant oscillatory error. This paper proposes a new modification for the conventional DFT-based phasor estimation method to improve its performance in the face of fault current signals containing DDC components. The proposed method accurately estimates both DDC components using the fault current signal and an auxiliary signal generated using high-frequency modulation. The averaging filter is applied to the fault current and auxiliary signal over one cycle, and then parameters of the DDC components are estimated using its three successive results. In the last step, the undesired effect of DDC components is eliminated from DFT output. The efficiency of the proposed method is validated through fault current signals generated by mathematical formulation and simulated using the PSCAD/EMTDC environment. The overall analysis of the obtained results demonstrates that the new modification makes the DFT method robust against both DDC components.