MODELING AND CONTROL OF UNIFIED POWER-FLOW CONTROLLER FOR TRANSIENT STABILITY

FACTS controllers are emerging as viable and economic solutions to the problems of large interconnected ne networks, which can endanger the system security. These devices are characterized by their fast respons e, absence of inertia, and minimum maintenance requirements. Thyristor controlled equipment like Thyristor Controlled Series Capacitor (TCSC ), Static Var Compensator (SVC), Thyristor Controlled Phase angle Regu lator (TCPR) etc. which involve passive elements result in devices of large sizes with substantial cost and significant labour for installat ion. An all solid-state device using GTOs leads to reduction in equipm ent size and has improved performance. The Unified Power Flow Controll er (UPFC) is a versatile controller which can be used to control the a ctive and reactive power in the Line independently. The concept of UPF C makes it possible to handle practically all power flow control and t ransmission line compensation problems, using solid-state controllers, which provide functional flexibility, generally not attainable by con ventional thyristor controlled systems. In this paper, we present the development of a control scheme for the series injected voltage of the UPFC to damp the power oscillations and improve transient stability i n a power system. (C) 1998 Elsevier Science Ltd. All rights reserved.