Optimum control strategies for transient as well as oscillatory instability of power systems

A co-ordinated dynamic braking strategy and excitation control to arrest the first swing instability as well as subsequent oscillations in a power system is proposed. Comparison is made between braking resistor, resistor-reactor and resistor-capacitor strategies with and without excitation control. The control strategies are obtained in terms of system states and other measurable quantities. Assumptions that the reference machine is large and that it is not equipped with dynamic braking facility lead to a simpler control strategy. Excitation strategy can also be significantly simplified by relaxing the constraints on the rotor angle. Computer simulation of a multi-machine system shows that a co-ordinated application of braking resistor-capacitor and excitation strategy controls the transients effectively.