Reduced step control of hypersonic vehicle based on tracking differentiator

Aimed at the strong nonlinearity, complicated couplings and high uncertainties of hypersonic vehicle, a reduced step control scheme based on high-order tracking differentiator is put forward. The longitudinal model of hypersonic vehicle is transformed as strict-feedback form. A tracking differentiator is imported in the backstepping frame. The derivative of virtual control signal in the first step is obtained using the tracking differentiator with its ability of estimating any derivative for a given signal. Also, the actual control signal in the second step is obtained according to the second-order derivative estimation of the tracking differentiator. Thus, the three design steps are reduced into two steps. Moreover, the parameter uncertainties and external disturbances are modeled as equivalent disturbances in each step. Extended state observers are designed to estimate the equivalent disturbances. Then, the equivalent disturbances are compensated in the controller. The Lyapunov theory is used to prove the stability of the closed-loop system. The numerical simulation results show the inhibiting ability of the proposed control scheme against uncertainties and disturbances. And its tracking precision is superior to that of the traditional dynamic surface control method.