Characterization of nonlinear loads in power distribution grid

Abstract

Electronic devices are complex circuits, consisting of analog, switching, and digital subsystems that require direct current (DC) for polarization. Since they are connected to the mains delivering alternating current (AC), however, AC-to-DC converters are to be introduced between the mains and the electronics to be fed. A converter is an electric circuit containing several subsystems, the most important being the switch-mode power supply, drawing power from the mains in pulses hence it is highly nonlinear. That happens, in reduced amplitude, even when the electronics to be fed is switched off. The process of AC-to-DC conversion is not restricted to feeding electronic equipment only. It is more and more frequently encountered in modern smart-grid facilities giving rise to the importance of the studies referred hereafter. The converter can be studied (theoretically or by measurements) as two-port network with reactive and nonlinear port-impedances. Characterization is performed after determining the port electrical quantities which are voltages and currents. Based on these data power and power quality parameters - power factor and total harmonic distortion- may be extracted. When nonlinear loads are present, one should introduce new ways of thinking into the considerations due to the existence of harmonics and related power components. In that way the power factor can be generalized to total or true power factor where the apparent power, involved in its calculations, includes all harmonic components. After introducing a wide range of definitions used in contemporary literature, here we describe our measurement set-up both as hardware and a software solution. The results reported unequivocally confirm the importance of the subject of characterization of small nonlinear loads to the grid having in mind their number which is rising without saturation seen in the near and even far future.