Robust two-time-level control strategy for sampled-data servomechanism problem

A two-level control strategy consisting of a fast first-level analogue controller for ensuring rapid reduction of tracking error under process disturbance without unacceptable overshoot and a slow second-level digital-analogue robust servo-mechanism controller to ensure asymptotic tracking with disturbance rejection is proposed. Thanks to the inclusion of samplers with an adequately chosen sampling period, the second-level controller comes into action essentially after the first-level controller has ceased its action. An interactive design procedure for the determination of the parameters of the controller is given. Simulation results comparing the proposed controller with conventional one-level controllers, such as the analogue, the digital and the digital-analogue controller, are presented.