Research and Develop on Unified Power Flow Controller with Solid-state Fault Current Limitter

Flexible AC Transmission System (FACTS) when used in traditional power system, can improve the transmission capacity of the power system and enhance the system stability and security. In FACTS family the unified power flow controller (UPFC) can achieve the flexibility to optimize control of the power flow and voltage (reactive power), with comprehensive regulating of the transmission line parameters-voltage, impedence and phase angle, therefore effectively enhance the power system dynamic performance and running quality. But UPFCmust be the fastest out of operation with the system to realize electrical isolatiaon when (near the installation point) short-circuit fault occurs, otherwise the series converter of UPFC can easily be burned because of withstanding the impact of the system high-voltage and short-circuit current in a very short time. This is also the main reason of UPFC realizing widely use in power system. Another FACTS device-SSFCL is capable of quickly limiting the short-circuit current to ensure the safety and reliability of the system.Combining the advatages of UPFC and SSFCL, a new type of FACTS device-UPFC-SSFCL is proposed. It is composed of UPFC and SSFCL by series coupling transformer. The device is equivalent to the conventional UPFC during normal operation of the power system and plays the tide of regulation power flow and voltage compensation function. When the system short-circuit fault occurs, it immediately limits the fault current to less than the set level as well as protect UPFC from high-voltage and short circuit impact of the current damage.The main circuit topology and characteristics, work principle of UPFC-SSFCL is introduced in the paper. Its control strategies (including the module independent and coordination of control strategies are more in-depth discussion. It also develops a 380V/3kVA model experimental prototype of UPFC-SSFCL, including the main circuit equipment (componets) parameters design, control programming, system modeling and simulation and experimental validation of the small model prototype. The results show that UPFC-SSFCL is capable of adjusting the power flow during normal operation and limiting the short-circuit current as well as protecting the device of its own security features during the short-circuit fault occurs.