A Two Time Level Control Strategy for a Robust Servomechanism Problem

A two level control strategy consisting of a fast first level analog controller ensuring rapid reduction of tracking error under process disturbances, without unacceptable overshoot, and a slow second level digital-analog robust servomechanism controller, to ensure asymptotic tracking with disturbance rejection, is proposed. The sampling periods are chosen so that the second level controller comes in to action essentially after the first level controller has `ceased its action.´ An interactive design procedure for the determination of the controller parameters is given. The LFC control of a two area power system is resolved using the proposed two-level control. Simulation results comparing the proposed controller with conventional one level analog, digital and digital-analog controllers are presented.