Equivalent-input-disturbance approach enables sliding-mode control systems to reject unmatched disturbances

The incorporation of an equivalent-input-disturbance estimator into a conventional sliding-mode control (SMC) system results in a new structure with improved disturbance rejection performance. This configuration enables an SMC system to reject unmatched disturbances. Simulation results for the positioning control of a dual-stage feed drive show that the method not only rejects unmatched disturbances, but also improves the disturbance rejection performance for matched disturbances, thereby demonstrating the validity of the design.