Experimental verification of the Generalized Nyquist stability criterion for balanced three-phase ac systems in the presence of constant power loads

Abstract

Stability is a great concern for power systems with relatively small sources and multiple regulated power converters. Addressing this need, this paper presents the experimental verification of the Generalized Nyquist stability Criterion (GNC) for balanced three-phase ac systems. This criterion, developed by MacFarlane and Postlethwaite in the 1970's, was proposed as a stability analysis tool for ac interfaces in the d-q frame in the late 1990's. Since then, however, very few papers have addressed the verification of this theory in a real power system given the intricacies of three-phase impedance measurement in the d-q frame. In this paper, a voltage source inverter feeding a boost rectifier is used to implement an experimental balanced three-phase system, where by adjusting their respective control bandwidths, stable and unstable cases are found at their ac interface. To this end, the d-q frame impedances of both converters are measured, and the GNC is applied, showing how both stable and unstable cases can be effectively predicted.