Power system stability through nonlinear control of excitation

Dynamics of power system has always been an area of major concern. Transient and small signal stability during perturbed conditions is of utmost importance for a power system engineer. Whenever there is a disturbance, the rotor angle oscillates and the speed of the machine deviates from the original nominal speed. The perturbation can be of various types. It could be a variation in the load, loss of a line or a unit or it could be the changes in the infinite bus voltage. During such cases, a Flexible AC Transmission System (FACTS) device can be introduced in order to improve the performance of the machine in terms of its speed variation. In this paper, a single machine infinite bus system (SMIB) is considered for studying the performance of a nonlinear Technique called Dynamic Inversion. It has been proved in this paper that speed of the machine can be maintained at synchronous speed through excitation control. In DI technique, zero error dynamics is enforced and the actual output is forced to follow the desired output. The terminal voltage of the infinite bus is assumed to be varying at certain intervals. The speed and the rotor angle are observed. The speed is forced to follow the desired value (synchronous speed) by using DI technique. The results obtained for the rotor angle and the angular frequency (speed) are found to be promising.