Improving power system dynamics by series-connected FACTS devices

This paper examines improvement of power system dynamics by use of unified power flow controllers, thyristor controlled phase shifting transformers and thyristor controlled series capacitors. Models suitable for incorporation in dynamic simulation programs for studying angle stability are analysed. A control strategy for the damping of electromechanical power oscillations using an energy function method is derived. The achieved control laws are shown to be effective both for the damping of large signal and small signal disturbances and are robust with respect to loading condition, fault location and network structure. Furthermore, the control inputs are easily attainable from locally measurable variables. The effectiveness of the controls are demonstrated for model power systems.