Operation of the unified power flow controller (UPFC) under practical constraints

The UPFC is the most versatile and complex power electronic equipment that has emerged for the control and optimization of power flow in electrical power transmission systems. It offers major potential advantages for the static and dynamic operation of transmission lines, but it brings with it major design challenges, both in the power electronics and from the perspective of the power system. As the UPFC transitions from concept to full-scale power system implementation, the control and protection of this sophisticated equipment are of primary concern. This paper describes the basic control, sequencing and protection philosophies that govern the operation of the UPFC, subject to the practical constraints encountered in an actual high power installation. The operation of the UPFC is illustrated with representative results from a TNA study, undertaken jointly by the Electric Power Research Institute (EPRI), Western Area Power Administration (WAPA) and Westinghouse Science and Technology Center (STC).