Sliding mode decoupling control of a generic hypersonic vehicle based on parametric commands

A sliding mode decoupling attitude controller based on parametric commands is proposed for a generic hypersonic vehicle (GHV). This vehicle model has fast time variability and strong coupling, is highly nonlinear, and includes uncertain parameters. The design of the controller takes these features into account. First, for the purpose of decoupling, the inner loop of the controller is designed using the dynamic inversion (DI) method. Input/output linearization is achieved using full-state feedback to globally linearize the nonlinear dynamics of selected controlled outputs. Second, to improve the robustness of the attitude control system, the sliding mode control (SMC) method is used to design the outer loop of the controller. Although the DI and SMC methods result in decoupling and robustness, there exists serious inconsistency between the commands of the attitude angles and the commands of the first-order differential of the attitude angles. To solve this problem and achieve a trade-off between dynamic response speed and attitude-tracking precision, we propose a parametric method for calculating the commands of the first-order differential of the attitude angles. Finally, simulation studies are conducted for the trimmed cruise conditions of 33.5 km altitude and Mach 15, and the responses of the vehicle to the step commands of pitch angle, yaw angle, and rolling angle are examined. The simulation studies demonstrate that the proposed controller is robust with respect to the uncertain parameters and atmospheric disturbance and meets the performance requirements of the GHV with acceptable control inputs.