Active Damping of Subsynchronous Resonance

Abstract: This report deals with the damping of sub-synchronous oscillations in power systems. The method is based on estimation of the generator rotor angle and shaft speed, by measuring the line current and the voltage across a phase-compensating series capacitor. These two signals are probably not sufficient, so a line-to-ground voltage measurement is added. However, this means increased costs. A thyristor-controlled series capacitor, TCSC, is used as a voltage source in aerial with the line. A control law that uses the estimated angle and shaft speed determines the TCSC voltage, in order to create an actively damping torque. The model is described in Chapter 2. This model holds only one oscillative mode. Simulations of a more sophisticated model, which has several oscillative modes, will thus be necessary. A stability analysis of the linearized model is carried out in Chapter 4. In Chapter 5, control strategies are derived, of which the first one is used in the rest of the report. The estimation problem seems to be the most crucial one. Different methods are discussed in Chapter 7. The linear Kalman estimator is chosen for the suggested controller structure in Chapter 8.

The problem of stability and parameter robustness are not completely analyzed. More work needs to be done in this field.