Removal of DC Offset Components by Using Two Auxiliary Signals

Digital relays face various challenges when estimating the fundamental phasor of fault signals. One of these challenges is the decaying DC components, which introducing because of line inductance. Therefore, simply, precisely, and quickly eliminating DC offset components will be very important. Since methods based on DFT have an imprecision in phasor estimation in the presence of DC offset, this paper provides an effective algorithm for eliminating and removing decaying DC from the fault signal and afterward calculating the fundamental phasor of the fault signal. In the proposed algorithms, at first, two new auxiliary signals are defined, and they have estimated parameters of DC offset. In the next step, two methods are provided to eliminate DC offset. In the first approach, the fundamental phasor was computed by applying DFT to the samples after their proper values were obtained by removing the DC offset from the fault signal. The second approach subtracts the DFT of the fault signal from the estimated value of the DFT of the DC offset. Comprehensive simulations have been run to assess the effectiveness and legitimacy of suggested algorithms.