Nonlinear Control For An Air-breathing Hypersonic Vehicle

In this thesis, the tracking control problem of an air-breathing hypersonic vehicle(AHV) is addressed. The dynamics of the air-breathing hypersonic vehicle is highlynonlinear, significant coupling and strongly afected by the flexible structural dynamic-s. Three nonlinear controllers are presented in this thesis. Lyapunov-Based theorem isutilized to prove that the designed control algorithm can achieve stable tracking whilekeeping all the close loop states bounded. Numerical simulation are performed on thenonlinear model to demonstrate the tracking performance of the controller, and highlightthe robustness with respect to the parameter uncertainties and external disturbances.The main contribution is presented as follows:At first, a new continuous robust controller is designed for the simplified control-oriented model of the hypersonic vehicle. We utilize the hyperbolic tangent function asthe nonlinear robust component to design the flight controller through the backsteppingapproach. And adaptive method is adopted to estimate the systems’unknown parameter-s. Compared with other existing works, our controller requires very limited knowledgeof the vehicle’s dynamic model, plus, it is continuous diferentiable, and is free of thechattering issue that sliding mode based control designs have. Lyapunov-based stabilitytheorem is employed to prove the asymptotic tracking of the vehicle’s velocity and flightpath angle.Secondly, considering the control design model including the elastic flexible modes,high-gain observer is employed to provide estimations for unknown nonlinear function-s which include flexible modes and additive disturbances. Then, the observer’s outputsare used in the feedback control design. Two subsystems, which are denoted as flexibleAHV dynamic subsystem and the observer subsystem respectively, are set up to facilitatethe stability analysis. Small-gain Theorem are used to analyze the inner connection be-tween the two subsystems and prove the result of ultimately bounded tracking of velocity,altitude and attack angle.At last, we presents a continuous robust adaptive tracking controller for an air-breathing hypersonic vehicle. To deal with the efects bring by the flexible dynamics,the nonlinear function in the dynamic model which is associated with flexible states isdivided into a tracking error related part and an amplitude bounded part. A matrix de-composition is utilized to decompose the uncertain unsymmetrical input matrix into theproduct of a symmetric positive-definite matrix and an unity upper triangular matrix to deal with the coupling between the altitude and attack angle. A modified parameter up-dating law which only depends on measurable states is designed to provide estimationsfor the unknown cross-coupling parameters. Lyapunov-based stability analysis is carriedout to prove the asymptotic tracking of the velocity, altitude and attack angle.