Transmission series power flow control

This paper presents the characteristics of two gate turn-off (GTO) thyristor voltage-sourced inverter-based series power flow control devices, namely the series power flow controller (SPFC) and the unified power flow controller (UPFC). These devices represent series extensions of the STATCON, an inverter-based shunt device developed under a tailored collaboration by EPRI, TVA and the Westinghouse Science and Technology Center, which will soon be placed in service on the TVA 161 kV transmission system for transmission voltage control. Operation of the SPFC and UPFC is illustrated through the use of easily-constructed circle diagrams on the P-Q plane. The circle diagrams provide the transmission planning engineer with a simple means to assess the performance of these devices on the transmission system. A concluding example illustrates that the UPFC provides a level of power flow control which is unattainable with more conventional devices