Modal Control Design of Damping Controllers for Thyristor-Controlled Series Capacitor to Stabilize Common-Mode Torsional Oscillations of a Series-Capacitor Compensated Power System

This paper proposes a unified approach based on modal control theory to design damping controllers of a thyristor-controlled series capacitor (TCSC) for stabilizing the inherent common-mode torsional interactions occurred in a series-capacitor compensated power system. The studied power system includes two nonidentical turbine-generator sets connected to an infinite bus through a common series-capacitor compensated transmission line. The employed TCSC is properly connected in parallel with a part of the series-capacitor bank of the compensated transmission line. The damping controllers of the TCSC employ the speed deviations of both turbine-generator sets as input signals to stabilize unstable torsional modes of the studied system by increasing the damping of these modes. Both frequency-domain approach based on eigenvalue analysis and time-domain scheme based on nonlinear-model simulations under different disturbance conditions are systematically performed. It can be concluded from the simulated results that the employed TCSC joined with the damping controllers designed by using modal control theory can effectively stabilize the common-mode torsional oscillations of the studied series-capacitor compensated system.