A study of equipment sizes and constraints for a unified power flow controller

This paper provides a quantitative measurement of the benefit that a unified power flow controller (UPFC) can provide to increase firm power transfer between two large power systems. Included is a complete model for a UPFC control system that contains bus voltage control by the shunt inverter, real power transfer between the shunt and series inverters, and real and reactive power control for the transmission line into which the series inverter is inserted. A significant part of the model is representation of dynamic limits that coordinate injected current limits for the shunt inverter, power transfer limits between inverters, voltage injection limits for the series inverter, current limits for the series inverter, and line voltage limits for the transmission line. This paper contains a simple system simulation to demonstrate the coordinated dynamic control and illustrate issues that system planning engineers must consider in defining applications for a UPFC.