Discrete Open Loop Control for Power Oscillation Damping Utilizing Variable Series Reactance Facts Devices

This paper describes an open loop method of controlling FACTS devices for power oscillation damping. The method is based on step-wise series reactance modulation. The principle of the method is to stabilize an oscillation in a power system which is characterized by one major mode of oscillation by switching a reactance in series with one transmission line, thereby changing the total reactance between the areas participating in the oscillation. In order to stabilize the system during an oscillation, the stationary voltage angle difference between the areas is changed to coincide with the present angle at a point where the speed of the lumped machine representations of the areas is nominal. This is the case at the peaks of the oscillation. To determine the required size of the reactance step, a reduced model of the power system is used. The model parameters are continuously updated using local measurements of the active power on the reactance controlled line. Several approaches for damping with different numbers of steps are presented and verified using digital simulations of power system models