Nonlinear Robust Flight Mode Transition Control for Tail-Sitter Aircraft

In this paper, the nonlinear robust control problem for tail-sitter aircraft in flight mode transitions is addressed. The problem is challenging due to the nonlinearities and uncertainties including parametric uncertainties, unmodeled uncertainties, and external disturbances involved in the vehicle dynamics during the mode transitions. The proposed controller is designed in two steps: first, the dynamic inversion technique is adopted to establish a tracking error model; then, for the tracking error model, a robust controller consisting of a nominal controller and a robust compensator is designed. The nominal controller is designed to obtain the desired tracking performances for the nominal system. The compensator is introduced to restrain the effects of uncertainties. Tracking errors of the closed-loop system are proven to converge into a neighborhood of the origin in a finite time. Simulation results are presented to demonstrate the advantages of the proposed controller, compared with the controller based on the standard loop-shaping method.