Flexible AC Transmission Systems

The main objective of flexible AC transmission systems (FACTS) controllers is to improve system stability: transient, voltage, and small‐signal, such that the AC transmission system becomes more reliable or additional power flow can be transferred on critical paths. This chapter discusses the use of FACTS controllers to accomplish these goals. It focuses on series compensation with fixed series capacitors and thyristor‐controlled series compensators for improving power system transfer capability and stability. The chapter describes FACTS based on both the thyristor and voltage‐sourced converter technologies. It also discusses the static var compensator (SVC) steady‐state operation, in which the SVC would regulate its terminal voltage precisely to a desired value in negligible time. The chapter describes the use of controllers based on a voltage‐sourced converter technology for AC‐DC conversion, allowing them to perform both reactive and active power control. It considers shunt controllers and series and coupled controllers.