Observer-based output feedback nonsingular terminal sliding mode control for systems with mismatched disturbances: Theory and applications

Abstract

This paper proposes an observer-based output feedback nonsingular terminal sliding mode control (OBOF-NTSMC) for systems with mismatched disturbances. Compared with available sliding mode controllers with mismatched disturbances, the merits of the proposed OBOF-NTSMC comprise: fast and accurate finite-time estimation is achieved; the assumption of the (global) constant bound induced for the observer design is relaxed; regardless of the system order, only one observer is required for the control design; the strict assumption of all states to be measurable is removed; and fast and precise finite-time regulation of the system output is ensured. The proposed OBOF-NTSMC has three main components: a variable gain finite-time sliding mode observer (VGFT-SMO), a nonsingular terminal sliding surface (NTSS), and a modified super-twisting reaching law (MST-RL). By designing the VGFT-SMO, we first reconstruct the unmeasurable output derivatives and the accumulated disturbance. Then, the NTSS is proposed such that in the sliding phase, the system output is driven to zero. Finally, the MST-RL is designed to drive the sliding variable to zero during the reaching phase. A rigorous investigation is carried out to establish finite-time convergence of the system output. Extensive applications are given to illustrate the superiority of the proposed OBOF-NTSMC.