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Laminated Low Temperature Co-Fired Ceramic Ferrite Materials for High Frequency POL Converters

Fig. 1. Ac system for GNC verification.
Stability is a great concern for power systems with relatively small sources and multiple regulated power converters. Addressing this need, this paper presents an 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 first proposed as a stability analysis tool for ac interfaces in the d-q frame in the late 1990s. 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 the ac interface. Then, 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.

Fig. 2. (a) Unstable case experiment results: System waveforms.
Fig. 2. (b) dd channel impedance.
Fig. 2. (c) Characteristic loci.
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