Study Of Nonlinear Methods For Longitudinal Control Of Hypersonic Vehicles

Hypersonic vehicle technology emerges from the integration of the highly development of the techniques in two fields:aeronautics and astronautics. This technology, involving in multi-disciplines, shows great potential applications both in military and civil industry. There are many hard problems still wait people from different disciplinary communities to answer, especially the hypersonic flight control remains as one of those critical unsolved issues and at-tracts many attentions from engineers and scientists. The non-standard dynamic characteristics and aerodynamic effects make the system modeling and controller designing highly challenge. Moreover, the wide range of speed during operation, intricate coupling between the engine and flight dynamics, and the lack of a broad flight dynamic database introduce significant varia-tions of plant parameters and uncertainties to the control problems. To meet the challenge in hypersonic control, this dissertation focuses on the investigation of novel control theory and methods for nonlinear control of hypersonic vehicle, taking longitudinal model as plant. The major contributions of this work are summarized as:(1) First, a quasi-continuous sliding mode controller (SMC) of3nd and4th order, respec-tively for altitude control law and velocity control law, has been designed for the tracking control of step-altitude and step-velocity command. Comparison of the results by this quasi-continuous high-order sliding mode control (QHSMC) with those by standard sliding mode control (SSMC) shows that QHSMC can significantly decrease the response time. In order to reduce the effects of chattering phenomenon, the order of the SMC is increased to4th and5th for altitude control and velocity control law respectively. Numerical results demonstrate that this method can dramatically reduce the chattering to the order of10-3while keeping the tran-sient dynamic responses as required. The robustness of the controller has also been studied for unknown but bounded disturbance. All the results justifies the effectiveness of the controller.(2) To deal with the non-compatibility between the uncertainties from the parameters of hypersonic vehicle and the disturbance in environments, a systematic design procedure is proposed to combine adaptive back-stepping control and exponential sliding mode control for the hypersonic vehicle in longitudinal direction. The motion equations of the hypersonic vehicle are first divided into two sub-systems of equations, one for speed and the other for altitude. The non-compatible disturbances are prescribed by a bounded function. Then, the Lyapunov functions for these two sub-systems are constructed step by step to formulate the adaptive back-stepping control and exponential SMC law so that the control system can track the command input and reach steady state along the designed sliding surface. To improve the robustness of the system, the adaptive back-stepping are modified to yield an adaptive sliding output tracking controller. The modification is carried out at the final step of algorithm by incorporating an appropriate sliding surface constructed in terms of the error coordinate. Theoretical proof and simulation results are presented. It is shown that this method can ensure the good performance for the tracking of a desired reference signal.(3) In order to capture the essence of uncertainties in hypersonic flight control model, the common external disturbances are considered as Brown process and Poisson process. As such, the hypersonic vehicle dynamic model can be taken as stochastic jump diffusion model. The linear state feedback control law is designed in terms of linear matrix inequalities, which usually are easy to be checked in a MATLAB Toolbox. Meanwhile, the stability theory of stochastic jump diffusion system has also proved in this dissertation. Simulation results justify the feasibility of this proposed method.