Robust Suboptimal Autopilot Design via a Novel Nonlinear Control Approach

This paper considers the problem of robust autopilot design for an air vehicle in the presence of model uncertainties and/or external disturbances. Considering the Mach number variations (as a slowly-varying parameter), the air vehicle is modeled as an uncertain nonlinear slowly-varying system. In this paper, first, a new robust stabilizing controller is designed for a class of nonlinear slowly-varying systems. The proposed controller has the nominal and robustifying parts. The nominal part of control law is also a suboptimal controller with respect to the Hamilton-Jacobi-Bellman equation. The robust part of the controller is designed according to a special sliding surface which is a combination of terminal and integral sliding surfaces. Moreover, it is proved that the robustifying part of the control law leads to vanishing the effects of the model uncertainties and external disturbances in a finite time. The proposed controller is then applied to autopilot design and simulation results confirm the efficiency of the proposed method.