Power quality index based on discrete wavelet transform

Abstract

Changing power system regulations and increased use of nonlinear devices have made power quality (PQ) a highly important issue. The short duration transient disturbances, along with the stationary harmonics have become very common due to the increased use of power electronic switches. These transients are defined in terms of their spectral content, duration and magnitude by IEEE 1159-2009 standards and are non-stationary in nature. The conventional PQ indices based on Fourier transform fails to indicate them, since Fourier transform gives amplitude frequency distribution and the time information gets void. In this paper, a PQ index, based on discrete wavelet transform (DWT) is proposed in order to determine the amount of deviation from the desired pure signal. The proposed PQ index is defined as the weighted sum of percentage energy deviation of the DWT details. The test system is simulated using ATP/EMTP software. Transients resulted from ten different switching instants covering a full cycle of the signal and having natural frequency ranging from 500Hz to 47kHz, are considered to validate the proposed index. The proposed index is also tested with the signals containing harmonics. Further, the proposed index is verified with the real signals acquired by the laboratory experimentation.