Stabilization of power systems using a variable structure stabilizer

A new technique for improving the dynamic stability of power systems is presented. This new technique makes use of the variable structure system theory and employs the generator speed to obtain a stabilizing signal to increase the damping torque of the synchronous machine.Although modern voltage regulator and excitation systems with fast response and high ceiling voltage can improve the transient stability by increasing the synchronizing torque, their effect on the damping torque is rather small. Under certain operating conditions, when the system exhibits negative damping characteristics, the voltage regulator usually aggravates the situation by increasing the negative damping. Hence, instability may result. In order to reduce this undesirable effect, it is useful to introduce supplementary stabilizing signals to increase the damping torque of the synchronous machine.This paper proposes a variable structure stabilizer for generating the required stabilizing signal. Simulation results indicate that the proposed stabilizer yields better system dynamic performance than that obtained by using the conventional and linear optimal stabilizers in that the step responses have less overshoot and a shorter settling time.It is concluded that the new stabilizer can be used as an effective means of increasing the damping torque and hence improving the dynamic stability of the power system.