Improved nonlinear dynamic inversion control for a flexible air-breathing hypersonic vehicle

This paper presents an improved nonlinear dynamic inversion control approach for the longitudinal dynamics of a flexible air-breathing hypersonic vehicle. The control design of the approach is based on a control-oriented model that represents the nominal state. By establishing a three inputs and three outputs control system, the control-oriented model in this study has full vector relative degree, without dynamic extension. To maintain tracking performance in the presence of disturbances, a nonlinear disturbance observer is adopted to estimate the disturbances. To achieve good transient performance, an adaptive damping term is proposed to the pitch dynamics. Based on approximate input-output linearization, linear control theory is applied to design a pole placement controller for the equivalent linear system. The damping ratio, natural frequency, and simple pole of the pole placement controller are optimized by the genetic algorithm along with the full nonlinear model of the vehicle. During the optimization, 11 uncertain parameters are introduced to the nonlinear model. Monte Carlo evaluation shows that the optimized pole placement controller provides robust tracking of reference trajectories. Simulation results indicate the effectiveness of the proposed control approach.