DWT analysis of high order harmonics influence over distorted regimes with fast variable loads

Abstract

The paper studies high order harmonics in distorted regimes with fast variable loads. Our experimental setup uses a three-phase load, built in laboratory by connecting in pairs, in different configurations, several laptops (from different manufacturers) across phases of a three-phase system. Our original dedicated data acquisition system acquired single phase waveforms, each of 5 periods, corresponding to phase currents and voltages, with a sampling frequency of 19 kHz. The acquired data were decomposed with a Discrete Wavelet Transform relying on our original function implementing a Daubechy filter of length 8. Considering the high variable operating regimes of laptops, the analysis was made individually for the first 4 periods of each analyzed sequence. Per period validations were performed considering the total RMS, calculated firstly according to definition, with a definite integral as the limit of a Riemann sum, and secondly as defined by Morsi, with DWT. 3-D diagrams were built to represent, for each level, the weights of details energy that we used as power-quality indices. The DWT analysis revealed that the weights of energies provided by harmonics with orders higher than 32 (sometimes 64) cannot be neglected when considering the signal's overall distorting residue, mainly for voltages. Transients were also detected on high order harmonics and the unbalance generated by them in the energetic picture was also discussed.