Harmonic analysis based on Discrete Wavelet Transform in electric power systems

Power Quality (PQ) evaluation for electric power system waveforms is realised using the harmonic analysis. The definitions of power-quality indices (PQIs) contained in the standards are based on the Fast Fourier Transform, which provides only an amplitude-frequency spectrum loosing time-related information. This paper proposes the reformulation of the PQIs definitions using Discrete Wavelet Transform (DWT) that preserves all information on time and frequency and reduces the problem of spectral leakages. The results obtained in the numerical example considering stationary and balanced single-phase system in sinusoidal situations indicate that the differences between DWT-based PQIs and the true values are very small. PQIs definitions were tested in the case of single-phase systems on waveforms captured using data acquisition system with Hall voltage and current transducers. To relieve the utility of this method the definitions were also extended to the unbalanced three-phase systems in the sinusoidal situation.