Characterization of fluctuating harmonics from single-phase power electronics-based equipment

The present paper is intended to analyze time-varying harmonic absorption of single-phase non-linear loads. To this aim, it is demonstrated that a continuous harmonic monitoring can be of a certain utility, since this practice allows a better characterization of harmonic spectra and an improved understanding of impact due to the various stages of typical operation. Some selected results obtained from a wide monitoring activity performed in a lab are reported in this paper. The results are relevant to NL appliances with power ratings ranging from less than 10?W to several hundred watts, such as desktop PC, printer (both laser and ink-jet), cell phone battery charger, and photocopier. The data thus obtained have been processed in order to determine probability density functions and distribution functions well evidencing the time-varying behavior of harmonic content of the absorbed current. Since a continuous harmonic monitoring allows to follow the nearly instantaneous evolution of the physical quantities (voltage and current) a cross-correlation based analysis of the various harmonic quantities among themselves is more meaningful than the monitoring activities providing longer observation time windows (up to minutes). The results obtained with such calculations can provide good indications for determining the origin of the time-varying behavior as evidenced.