Subsynchronous resonance. A controller for active damping

This paper proposes a method for elimination of subsynchronous oscillations in power systems. The method uses only measurements available at the series capacitor located anywhere at the transmission line. The generator rotor position and angular velocity are estimated and a thyristor controlled series capacitor (TCSC) is used to create an active damping torque that rapidly damps all subsynchronous oscillations of the turbine-generator system. It is shown that subsynchronous resonance is a linear stability problem, i.e. even the linearized model is unstable, and so a linear Kalman filter can be used for the estimations.