Robust disturbance rejection based on equivalent-input-disturbance approach

A robust disturbance rejection method for uncertain systems is presented in this study. It effectively rejects both matched and unmatched disturbances and guarantees robust stability of the system when there exist modelling uncertainties. First, the authors show the configuration of the system that is based on the idea of the equivalent input disturbance (EID). An EID estimator is designed to compensate disturbances without requiring their prior knowledge. Then, a robust stability condition and the method of the controller design are presented using a linear-matrix-inequality. Finally, the validity of the authors method and its superiority over a conventional control method and the sliding-mode control method are demonstrated through the simulations of a numerical example and experiments of a rotational-speed control system.