On-off control of an active load for power system damping-theory and field test

Controlled resistive loads can contribute to damping of electro-mechanical oscillations. This paper presents an on-off damping controller for a single machine system. It was used at a field test in Southern Sweden to damp oscillations of a 0.9 MW hydro power generator. The controller used estimated machine frequency as input and controlled a 20 kW resistive load via thyristor switches. The field measurements are compared to time simulations and a systematic procedure for tuning the controller is given. The results indicate that on-off control of active loads is effective in terms of added damping and that it is simple to tune and implement.