Mixed H2/H∞ robust adaptive control of hypersonic vehicles based on the characteristic model

This paper is concerned with the mixed H2 and H∞ adaptive control of hypersonic vehicles longitudinal dynamics during reentry phase. The dynamics of the angle of attack in the longitudinal plane is modeled by a second-order difference equation known as the characteristic model. In order to improve the transient performance in the presence of large aerodynamic coefficients change and unknown exogenous disturbances, a more intelligent golden-section adaptive control law is proposed based on our previous work. In addition to the easy implementation and stability before the convergence of parameter estimation, this new adaptive control law contains an adjustable parameter λ(k) that guarantees H2 and H∞ robustness of the system, and is calculated based on the linear matrix inequality approach. The integration of adaptive control and robust control provides the attitude system of the hypersonic vehicle with the capability to accommodate large flight conditions in a reliable way. Experiments are carried out on a hypersonic vehicle with a high lift-drag ratio during the reentry phase, and the effectiveness of the control scheme is verified.