Nonlinear adaptive control for hypersonic vehicles via immersion and invariance

A new nonlinear adaptive control scheme for the angle of attack of a hypersonic vehicle is presented in this paper. The new scheme is based on the immersion and invariance (I&I) methodology, aiming to tolerate various uncertainties. The control system has a modular structure consisting of the design of control law and the estimates of the unknown parameters, which can be tuned independently. Unlike the certainty-equivalent adaptive control, the parameter estimates of the I&I theory have an additional term which is a judiciously chosen nonlinear function. This term allows for shaping the dynamics of the estimation errors (off-the-manifold dynamics) to have stable zero equilibrium. The stability analysis based on a composite Lyapunov function for the closed-loop system is performed to show the asymptotical convergence of the tracking error. The proposed I&I adaptive controller is simulated in two kinds of conditions, both obtaining results of a fast response and an accurate tracking, which shows the effectiveness of the proposed approach.