Abstract: An adaptive terminal sliding mode control method based on the inner-loop and outer-loop systems is designed and analyzed for the longitudinal dynamics of air-breathing hypersonic vehicles under control input constraints. Considering the angle of attack and the pitch rate as the states of the inner-loop system with aeroelastic modes and disturbances, an adaptive terminal sliding mode control law of the elevator deflection is proposed based on backstepping design. Considering the velocity as the state of the outer-loop system, a dynamic inversion adaptive control law of the equivalence ratio is also obtained based on dynamic inversion design. Moreover, two multilayer neural networks are used for the approximation of the saturation property of two control inputs, respectively. Based on Lyapunov stability theorem, all signals of the closed-loop system are bounded and exponentially converge to the neighborhood of the origin globally. Furthermore, aeroelastic modes of air-breathing hypersonic vehicles are asymptotically stable. Simulation results demonstrate the effectiveness of the proposed control method in saturation alleviation of the longitudinal dynamics of air-breathing hypersonic vehicles. In additional, the control method not only realizes the control aim, but also improves transient performance of the controlled system.

Key words: hypersonic vehicles, control input constraint, adaptive control, sliding mode control, neural network