Autopilot Design and Analysis for Hypersonic Vehicles Using Nonlinear Adaptive Control Approaches

This paper provides a longitudinal control loop design method for hypersonic vehicles based on feedback linearization control (FBLC) in combination with disturbance observer-based control (DOBC). Based on an analysis of the dynamics of hypersonic vehicles and their model uncertainties, a cascade control structure consisting of flight path angle, acceleration, and pitch rate control loops is herein proposed. A pitch rate control loop was designed to compensate for model uncertainties caused by aerodynamic model errors and unknown propulsion-aerodynamic coupling effects. These model uncertainties were estimated through the DOBC technique in the proposed method. Additionally, the behavior of the tracking errors and observer estimation errors in the control loop was analyzed using the Lyapunov stability theory. To provide useful insights into the proposed control loop, the connections between the proposed control loop structure and conventional control loop structures were examined. The proposed control loop was found to be equivalent to a 3-loop autopilot structure and incremental nonlinear dynamic inversion (INDI), providing new insights into nonlinear and adaptive control techniques. Furthermore, simulation results demonstrated that the proposed control loop can effectively estimate model uncertainties, offering good tracking performance even in the presence of model uncertainties.