Disturbance Observer Based Fixed-Time HOSM Controller Design

This paper investigates high-order sliding mode (HOSM) control for nonlinear systems affected by mismatched disturbances and output constraint. A new control strategy is introduced, incorporating a fixed-time disturbance observer (DO) and a fixed-time HOSM controller. Initially, the fixed-time DO is utilized to assess the mismatched disturbances. Subsequently, to address output constraint, the Barrier Lyapunov Function (BLF) is employed. The fixed-time HOSM controller is then systematically developed by integrating the BLF with the power integral technique. This approach guarantees the fixed-time stability of the closed-loop system, with a setting time that remains unaffected by the initial state, while also adhering to pre-defined output constraint. The effectiveness of the proposed theoretical framework is demonstrated through an example involving a BUCK voltage converter operating under varying loads.