An Improved Least Square Error Algorithm for Digital Relaying

In this paper a combination of the least square error algorithm (LSE) and decaying dc component estimation method is applied to extract the phasors of both fundamental and harmonic elements. LSE has been widely used for voltage or current phasor extraction because of its simplicity. Nevertheless, the LSE technique has certain disadvantages regarding its heavy computational burden and its disability in accurate estimation of decaying dc component, which cause mal operation, especially in distance relays. To overcome these drawbacks, it is necessary to modify the LSE. In this paper, at first, the decaying dc component is estimated and eliminated by subtracting the dc value from fault current signal after one cycle from the fault instant and finally the LSE algorithm is used with the goal of estimating the magnitude and phase of both fundamental and harmonic elements of the fault current signal. In order to validate the performance of the proposed algorithm, computer simulated signals generated by MATLAB are performed. The proposed method has been evaluated and compared with the conventional LSE for a wide variety of signals including different levels of decaying dc magnitude and time constants. In order to evaluate and compare the proposed method comprehensively, standard performance indices including rise time, settling time and overshoot are considered in this study. The simulation results demonstrate the accuracy of our proposed method in phasor extraction in comparison with conventional LSE algorithm.