Augmented fixed‐time observer‐based continuous robust control for hypersonic vehicles with measurement noises

This study is concerned with the augmented fixed‐time observer based adaptive super‐twisting cruise control for flexible air‐breathing hypersonic vehicles (FAHVs). First, the input–output linearisation technique is employed to derive a control oriented FAHV dynamic model. Then, a super‐twisting controller is designed to track the reference velocity and altitude commands when faced with various uncertainties and disturbances. In addition, a novel gain adaptation law is constructed as a supplement of the super‐twisting controller to avoid overestimating the values of controller gains. The adaptation law keeps the controller gains adapting dynamically to guarantee the finite‐time convergence of sliding variables in the presence of disturbances with unknown boundaries. Moreover, augmented fixed‐time observers are designed to estimate the true values of measured states and filter out high‐frequency sensor noises. Thus, the fixed convergence time of these observers is achieved independently of initial estimation errors. Finally, the augmented fixed‐time observers and adaptive super‐twisting controller are combined together to ensure the superior tracking performances of FAHVs under the effects of uncertainties, disturbances, and measurement noises.