Innovative techniques in modeling UPFC for power system analysis

The unified power flow controller (UPFC) is a flexible AC transmission system (FACTS) device capable of controlling line flows and terminal voltage. In order to analyze its true effects on power systems, it is important to model its constraints due to various ratings and operating limits. Innovative techniques are introduced in this paper for fast power flow convergence with various UPFC control modes and simultaneous multiple limits enforcement, while the line side bus remains explicitly accessible. An efficient algorithm is developed for applying the line side voltage limits, which avoids the possible hunting between shunt and series converters of UPFC. Control models with similar constraints are also developed for stability studies. Simulations are performed using EPRI´s Power System Analysis Package (PSAPAC)