A novel analytical method for DC offset mitigation enhancing DFT phasor estimation

This paper introduces a new technique to remove DC offset (DCO) in fault current based on current second-order derivation to enhance the phasor estimation process. In this method, adding the (fault current) FC and a given coefficient of second-order derivative (SOD) of FC yield to calculate DC offset quantity in a simple analytic approach. Discrete Fourier transform (DFT) is only able to determine harmonics with a specific frequency, not with wide range variation like DCO. In this paper, a simple method is proposed to filter DCO from the main signal and prepare pure sinusoidal input for the DFT function. This pre-processing method prepares a signal without DCO for accurate phasor estimation in discrete Fourier transform (DFT) which is widely used for frequency estimation in protection systems. A set of different scenarios were considered to evaluate the proposed method with other practical methods. The results with computer-generated and simulation-based signals show that the proposed method is simple and more accurate to calculate DCO.