Power system small signal stability analysis with FACTS elements

FACTS (Flexible AC Transmission Systems) elements include low frequency electronic switching devices which result in periodic but nonsinusoidal voltage and current waveforms. Methods based on the assumption of sinusoidal waveforms may not be accurate enough for systems with FACTS elements, while averaging methods work well for high frequency switching systems but they are less accurate for systems with low switching frequencies. This paper presents a rigorous methodology for small signal stability analysis of systems with FACTS elements and nonlinear elements. The method consists of: (a) FACTS and nonlinear device modeling, (b) system periodic steady state analysis and (c) system eigenvalue analysis. The methodology is compared to the averaging method and its capabilities are demonstrated with example systems.