ABSTRACT
In the previous chapter, we considered the application of series and shunt FACTS controllers for stabilizing an SMIB system when subjected to a major disturbance (three-phase fault followed by clearing). The objectives of the controllers are to (a) ensure that the system is transiently stable in the first swing and (b) damp the nonlinear oscillations (of power flow, generator rotor angle) and steer the system trajectory close to the postfault equilibrium state, which is assumed to be stable. Once the system state is close to the stable equilibrium point, the emergency control action can be discontinued. In the literature, such control action has been termed as discrete in contrast to the continuous control action by power swing damping controllers, which are auxiliary or supplementary controllers in conjunction with power scheduling or voltage regulating controls. It is to be noted that damping controllers are designed to stabilize the system under normal operating conditions when generation is able to meet the varying load demand, without violating any inequality or transient stability constraints. The control action by these damping controllers is limited to prevent adverse interaction with voltage regulation or power scheduling control functions.
