Conversion Flight Control For Tilt Rotor Aircraft Using Nonlinear Time-Varying Perspective

Unlike the popularly used approaches (in which the time-varying nature of the system's dynamics is neglected), a Lyapunov-based nonlinear time-varying framework is provided to handle the longitudinal control of tilt rotor aircraft during conversion flight. The conversion flight control problem is regarded as the trajectory-tracking problem with respect to a desired generalized conversion corridor. Introducing the concept of a virtual plane, the design procedure is boiled down into two steps: the design of the virtual controller and the distribution of the actual control inputs. Firstly, aimed at the nonlinear time-varying control-oriented model, a virtual controller that renders the globally uniformly exponential stability of the origin, together with a constraint to alleviate the input saturation, is given with rigorous theoretical proof using the sum-of-squares (SOS) technique. Next, a practical control allocation strategy is adopted to achieve the deflections of the actual control surfaces. To enhance the robustness of the controller, a nonlinear disturbance observer is proposed to estimate the influence of the uncertainties of the aerodynamic parameters and modeling errors.