A novel nonsingular fixed-time sliding mode control for morphing aircraft with actuator faults and saturation

Abstract

This paper proposes a fixed-time anti-saturation adaptive sliding mode control (FxASASMC) methodology to solve the challenge of attitude tracking control in morphing aircraft under actuator faults, saturation and external disturbances. The proposed control algorithm consists of three key components: a novel nonsingular fixed-time sliding mode surface, a fixed-time anti-saturation compensator, and a continuous fixed-time adaptive control law. The novel nonsingular fixed-time sliding mode surface is developed based on the arctan function, enabling not only the confinement and independence of the sliding modes' convergence time from the initial states but also the benefit of a smaller initial value, thereby assisting in saturation avoidance. To mitigate the saturation issue, a fixed-time anti-saturation compensator is employed. Moreover, throughout the control process, the anti-saturation compensator ensures that the output is bounded. And once the actuator saturation stops, its output converges to zero in a fixed time, which effectively minimizes the impact of the anti-saturation compensator on the control system performance in the absence of system saturation. Based on the sliding mode surface and anti-saturation compensator, the continuous fixed-time adaptive control law ensures that the attitude tracking errors converge toward the neighborhood of the origin in a fixed time, even if the boundaries of the complex disturbance are not known in advance. Moreover, the convergence time boundary remains unaffected by the initial errors. In parallel, the control command remains continuous and free of chattering. Ultimately, the proposed control scheme's effectiveness and enhanced performance are demonstrated through various numerical simulations.