An ESO-based Attitude Control Method for Non-affine Hypersonic Flight Vehicles

This paper addresses the attitude tracking control problem of the hypersonic flight vehicles with non-affine formulations. The command filter is introduced for obtaining the first and second derivatives of flight path angle and solving the "explosion of complexity" problem existing in application of backstepping. A tracking differentiator is designed to estimate the disturbance term in the dynamics of angle of attack. For the unknown dynamics of the pitch rate including non-affine terms, it is transformed into a new form first, and then an extended state observer is employed to estimate the unknown part. The stability of the closed-loop system is proved via the Lyapunov theory. In comparison with the existing methods, the remarkable advantages of the proposed method are that it can be applicable to all flight conditions, relaxes the restriction on the disturbance term existing in the dynamics of angle of attack, and considers the possible saturation of control input. Finally, a contrastive simulation is presented to demonstrate the effectiveness of the proposed method.