Fractional-order PI^λD sliding mode control for hypersonic vehicles with neural network disturbance compensator

This paper proposes a novel fractional-order PI^λD sliding mode controller for a nth-order nonlinear system with compound disturbance. The novel method contains a fractional-order term in the sliding mode surface compared with the traditional sliding mode controller. The nth-order nonlinear system with disturbance is firstly investigated. Then the effects of the fractional-order PI^λD sliding mode controller with different fractional-orders are studied and the effect is compared with PID controller. Finally, the fractional-order sliding mode controller is designed for hypersonic vehicles. Moreover, in order to combine the advantage of fractional-order sliding mode control with neural network, a fractional-order sliding mode controller with neural network observer is proposed for hypersonic vehicles in this study. The neural network observer is introduced to approximate the compound disturbance and relax the requirement of the switching gain. Based on Lyapunov stability theory, the attitude-tracking errors are shown to be asymptotically stable. The simulation results show that the proposed control scheme achieves satisfactory control performance compared with PID controller and is robust against compound disturbance.