Effective Value Calculation Using Wavelet Transform

The process of calculating the effective values of voltage and current root mean square (RMS) using Fourier transform (FT) suffers a high computational effort. Since it provides only an amplitude-frequency spectrum, looses time-related information, and is unable to deal with no stationary waveforms, standard definitions are reformulated in the time-frequency domain using the wavelet transform (WT). The wavelet transform is a powerful tool because it is able to preserve time and frequency information, decreases the computational time and effort by splitting the frequency spectrum into bands or levels. Furthermore, it is able to represent different degrees of distorted waveforms more precisely than FT. In this case, the spectral leakage can be reduced by appropriate selection of the wavelet family and the mother wavelet. When a voltage or current waveform is decomposed and analysed using wavelet transform, the wavelet coefficients can be used to calculate effective values in a way similar to that in the frequency domain using Fourier series. The results obtained by applying the IEEE Standard definitions and the DWT-based definitions for effective RMS show that the differences related to DWT are very small. Key-Words: wavelet transform (WT), power quality, electric power components, root mean square (RMS), multi-resolution analysis (MRA), wavelet family, mother wavelet, data acquisition system