Modeling and damping strategy for active power oscillation of static var generator

The outer voltage control loop is critical important to Static Var Generator (SVG) because it directly relates to the stability of DC voltage. The low frequency active power oscillation of SVG indicates that there may be some interactions when the outer voltage loop is taken into consideration. However, there is no valid and concise model to analyze the mechanism and characteristics of the low-frequency oscillation. This paper firstly analyzes the active power balance between a single-phase SVG's AC and DC side, and establishes a general dc equivalent impedance model reflecting this power balance and DC voltage fluctuation. The Nyquist stability criterion is adopted to present this unstable low-frequency interaction characteristic. The analysis results show that the oscillation frequency is closely related to the outer voltage control loop and the impedance of grid. To suppress oscillation, a DC voltage droop control method is proposed to dampen out the power oscillation. Experiments are carried out on a SVG, and the results validate the correctness of the model, the analytical results and the suppressing scheme.