An improved morphological transform filter for fundamental frequency phasor measurement of power system

Abstract

The fundamental frequency phasor measurement method based on Fourier transform is affected by the decaying DC offset in fault current. To reduce this effect, a morphological transform filter (MTF) has been proposed to filter out the decaying DC offset. However, this filter is affected by fault inception angle, which makes it difficult to deal with some specific types of fault currents. Therefore, an improved morphological transform filter (IMTF) is proposed in this paper. The proposed IMTF eliminates the influence of fault inception angle by averaging the results of the morphological transform of two adjacent half-cycle. By simplifying the morphological operation of MTF, IMFT has a lower calculation burden. The real-time performance of IMTF is ensured by compensating the waveform over one cycle. Simulation studies are carried out on Matlab/Simulink and RT-Lab system, respectively, and the results show that the proposed IMTF outperforms MTF in terms of robustness. Besides, fault data recorded from the digital fault recorder is also used to test the practicability of IMTF.