Analysis of Voltage Stability in Electric Power System with UPFC
Impact of FACTS devices on the voltage stability is usually determined with the power-flow calculations. Results, gained in this way, is sometimes difficult, if not impossible, to explain in qualitative way and to draw the general conclusions. Therefore analytical approach using simple basic models may submit more insight into basic features of tested device behavior in an electric power system (EPS) than numerical calculations at real-like system model. The paper presents such an approach for Unified Power-Flow Controller (UPFC), which may be considered a synonym for multi-parameter controlled FACTS device. The basic goal is to acquire impact of an UPFC on voltage stability enhancement and voltage control respectively. Therefore it is positioned into the standard model, widely used for voltage stability representation purposes. In the paper the mathematical solution of the problem is explained and the impact of the UPFC on voltage stability is shown.