Generalized Phasor Estimation Method Based on DFT with DC Offset Mitigation

This paper proposes a generalized discrete Fourier transform (DFT) based dc offset mitigation method to improve the accuracy of phasor estimation during faults. The DFT is applied to the signal and the results are separated into multiple sets, where each set contains the information of both the fundamental frequency component and the decaying de offset of the signal. This formulation enhances the redundancy of the dc offset estimation problem. Afterwards, the dc offset is as the unknown to be estimated and the state estimation procedure is adopted to solve this problem. The proposed method provides a generalized framework for phasor estimation with full consideration of problem redundancy. Numerical experiments validate that the proposed method presents higher phasor estimation accuracy compared to the existing phasor estimation methods. Furthermore, the proposed method also demonstrates robustness against measurement noises.

I. Introduction

Power system protective relaying and fault location play irreplaceable roles in modern power systems to ensure safety and the reliable operation of the power systems. During faults, the fault current signal typically contains decaying dc offset, fundamental frequency component and higher order harmonics. Accurate fundamental frequency phasor estimation is essential for proper operations of the fundamental frequency phasor based protective relaying (distance protection, line differential protection [1], etc.) and fault location (impedance based methods [2], other phasor domain approaches [3], etc.). To address this issue, researchers proposed phasor estimation methods to obtain the fundamental frequency phasor from the fault signal [4]–[8].