Robust Tracking Controller Design For Hypersonic Vehicles

Hypersonic vehicles have an outstanding penetration ability and detection performance, and it can offer a great help to expand battle space. Hypersonic vehicles have special strategic value in both military and civilian areas. Therefore, it has already become a hotspot in the research of all the countries throughout the world. The hypersonic vehicles are designed integrated. Compared with common airplane or flight vehicles, the coupling exists between the airframe and the engine. There is a more complex flight condition for hypersonic vehicles. The stability will be greatly influenced by time-varying uncertainties. Lots of factors have brought great challenges to the control system designing of the hypersonic vehicles.In this thesis, based on the generic hypersonic vehicle longitudinal model developed by NASA Langley research center, the related researches are carried out to design tracking controllers for both of the linear hypersonic vehicles model and nonlinear model with time-varying uncertainties. The main work is listed as follows:Firstly, analyzing the full-state differential equations of the hypersonic vehicle model and introducing the basic structural parameters. Besides, each sub-models of the hypersonic vehicle is given in this paper. Then the longitudinal dynamics equations under the usual coordinates are obtained by decoupling analysis. Further study is carried out for the particular characteristics and aerodynamic properties of the hypersonic vehicles.Secondly, the linearization model of the hypersonic vehicle is obtained based on some reasonable conditions. Considering the time-varying uncertainties in flight for the hypersonic vehicle, the system model with time-varying uncertainties can be obtained, where the lower and upper bounds of the unknown time-varying uncertainties can be estimated in the state of flight. A novel robust tracking control design method is proposed for the model mentioned. Compared with traditional robust controller with fixed gains, the method presented has better capability to deal with large time-varying parameter perturbation and enhance the robustness of hypersonic vehicle. Sufficient conditions for controller design are given in the framework of robust optimization technique, and the controller gains is on-line adjusted according to the designed switching-laws. The proposed robust tracking controller can not only guarantee the stability of hypersonic vehicle, but also track the command signal about height and speed quickly, even in the case of external disturbance existing.Thirdly, considering the actual flight states of the hypersonic vehicles, the designed controller can be separated for velocity and altitude control respectively according to the characteristics of this model. In the case of height controller, the strict-feedback form equations of hypersonic aircraft can be got based on some reasonable conditions, and then RBF neural network is used to approximate the unknown portions of the model under the assumption that all subsystems have uncertainties. Finally, the DSC-based control approach is used to track a desired altitude trajectory. The controller for velocity is designed by traditional nonlinear control method. And the control method can maintain airspeed at the neighborhood of the desired velocity. The simulation results show that the accurate tracking control of hypersonic vehicle about altitude and velocity can be realized by using the proposed approach.Concluding remarks are presented at the end of this dissertation. Some open problems are also pointed out, which deserve further study.