Nonlinear robust controller design for hypersonic vehicles

Hypersonic vehicles are characterized by high model nonlinearity, strong coupling, large parameter uncertainties, and low disturbance rejection, which pose a challenge for their automatic controller design. We propose a nonlinear robust control method based on the robust compensation technique and feedback linearization method. The feedback linearization method is firstly applied to achieve the output/input linearization for the longitudinal model, resulting in a linear model. Then, a linear robust controller consisting of a nominal controller and a robust compensator is designed for the obtained linear model. The nominal controller is designed based on the pole assignment algorithm to guarantee the outputs of the nominal linear closed-loop system to track the desired references, while the robust compensator is introduced to restrain the effects of parametric uncertainties and external disturbances on the closed-loop control system. Based on the small gain theorem, the robust stability and the robust tracking properties are proved. Numerical simulation is implemented to validate the higher effectiveness and more advantages of the proposed nonlinear control method over the nonlinear loop-shaping control method.