Wavelet representation of voltage flicker

Voltage flicker can be considered as a voltage magnitude modulated signal with a frequency ranging from 0.5 to 30 Hz. Wavelet transform is a powerful tool to analyze this kind of nonstationary, wide-range frequency signal. The wavelet representation of voltage flicker signal is presented in this paper. The proposed scheme is implemented in three steps. Firstly, a low-pass demodulation filter is designed to find the magnitude of 60 Hz component. Accordingly, a high degree of accuracy may be achieved and the effect of the transient, harmonics and white noise may be eliminated. Secondly, a multiresolution analysis (MRA) scheme that is an orthonormal wavelet transform, can then be applied to decompose the demodulated signal into several components according to the scales. Components at high scale can be considered as white noise, while components at the low scale represent the voltage fluctuation. The smooth version left by the MRA scheme represents the DC component. Finally, the voltage flicker level can be estimated by the wavelet coefficients at different scales, which give the time and frequency information. Numerical examples are also presented in this paper to show the efficiency of the proposed scheme. (C) 1998 Elsevier Science S.A. All rights reserved.