Damping interarea and torsional oscillations using FACTS devices

A problem of interest in the power industry is the mitigation of interarea and torsional oscillations. Interarea oscillations are due to the dynamics of interarea power transfer and often exhibit poor damping when the aggregate power transfer over a corridor is high relative to the transmission strength. These oscillations can severely restrict system operations and, in some cases, can lead to widespread system disturbances. Torsional oscillations are induced due to the interaction between transmission system disturbances and turbine-generator shaft systems. The high torsional stresses induced due to some of these disturbances reduce the life expectancy of the turbine-generators and, in severe cases, may cause shaft damage. This thesis reports the development of novel control techniques for Flexible AC Transmission System (FACTS) devices for the purpose of damping power system interarea and torsional oscillations. In this context, investigations are conducted on a typical three-area power system incorporating FACTS devices. The Genetic Algorithm (GA) and fuzzy logic techniques are used for designing the FACTS controllers. Although attention is focused in the investigations of this thesis on the Unified Power Flow Controller (UPFC), studies are also conducted on two other FACTS devices, a three voltage-source converter Generalized Unified Power Flow Controller (GUPFC) and a voltage-source converter back-to-back HVdc link. The results of the investigations conducted in this thesis show that the achieved control designs are effective in damping interarea oscillations as well as the high torsional torques induced in turbine-generator shafts due to clearing and high-speed reclosing of transmission system faults. The controller design procedures adopted in this thesis are general and can be applied to other FACTS devices incorporated in a power system. The results and discussion presented in this thesis should provide valuable information to electric power utilities engaged in planning and operating FACTS devices