Robust nonsingular Terminal sliding mode backstepping control for air-breathing hypersonic vehicles

A new nonlinear disturbance observer based Terminal sliding mode backstepping controller is proposed for flexible air-breathing hypersonic vehicles with parameter perturbations and external disturbances. The longitudinal vehicle model considering the elastic mode is expressed as strict feedback form. On the basis of traditional backstepping method, the nonsingular fast Terminal sliding mode is introduced to control the pitch angle and pitch rate, thus optimizing the control structure and enabling the system with finite time convergence property. A new nonlinear disturbance observer developed from tracking differentiator is then introduced to estimate and compensate the uncertainties including the derivatives of virtual control laws to improve the robustness of the controller, which avoids the explosion of differentiation terms. The system tracking error is proven to converge to zero in finite time with Lyapunov stability theory. Simulations demonstrate the effectiveness of tracking input commands with the designed controller in the presence of uncertainties.