On control of gate controlled series capacitor for SSR and power oscillation damping

The subsynchronous resonance (SSR) phenomenon may occur when a steam turbine-generator is connected to a long transmission line with series compensation. In this paper, to mitigate SSR, two control methodologies for turn-off angle control of the gate-controlled series capacitor (GCSC) are presented. The first methodology is an open-loop control that uses the line current frequency oscillations to generate proper turn-ff angle for the GCSC. The second one is a closed loop control that is based on the Takagi-Sugeno (TS) fuzzy logic controller. The study system was modified from the IEEE First Benchmark Model by changing a part of the fixed series capacitor to the GCSC. The MATLAB® program was used to verify the effectiveness of each control methodology. Three different GCSC ratings were analyzed. It is shown that using an open-loop control methodology, in some GCSC ratings, the SSR can be properly damped. It is also shown that using TS fuzzy control methodology, not only SSR but also electromechanical power oscillation can be effectively damped.