ABSTRACT Accurate phasor estimation for transient currents during power system faults is challenging due to the presence of exponentially decaying DC offsets. Existing discrete Fourier transform (DFT)‐based methods often inadequately address this issue by assuming only a single decaying DC offset. This paper proposes an improved DFT‐based phasor estimation method designed to effectively eliminate the influence of double decaying DC offsets. The method models the fault current as a composite signal containing the fundamental frequency component, harmonic components, and two decaying DC offsets. By segmenting a one‐cycle data window into multiple subsets, it constructs a complex equation system from the DFT results of these subsets, which incorporates the parameters of two decaying DC offsets and the fundamental frequency phasor. An analytical solution for the accurate fundamental frequency phasor is then derived. Simulation results demonstrate that the proposed method achieves smaller magnitude and phase angle errors compared to the classic DFT method and existing methods assuming a single decaying DC offset. Field data of transient currents in a 500 kV practical power system also show the effectiveness of the proposed method over existing ones.
Liu et al. (Thu,) studied this question.