Abstract

The main objectives of Flexible AC Transmission Systems (FACTS) devices are to increase the transmission capacity of lines and to control the power flow over designated transm-ission system. FACTS devices can perform all objectives of reactive power control and voltage control required for transm-ission and lines. Several schemes of flexible AC transm-ission systems FACTS are in use today. One of the most important FACTS devices is the Unified Power Flow Controller (UPFC), which is used for series voltage injection in desired phase as shown in Fig 1. The (JPFC is a combination of a static Compensator (STATCOM) and a static synchronous series compensator (SSSC), which are coupled via acommon DC link.