Multi-modal Switching Control Study For Near Space Morphing Vehicle

Near Space Vehicle usually works in the region of the 20 ~ 100 km of near space, which has advantages of high cost-effective, long-endurance, high-resolution, good maneuverability, so the study of Near Space Vehicle is attached great importance by the world's military powers. However, the NMV not only has the characteristics of strong nonlinearity, rapid time-varying, strong coupling and uncertainty, but also a problem of winglet changing. So the research on the control of different flight modes and multi-mode switching of the NMV is a challenging job. This thesis focuses on the study of establishment of nonlinear mathematical model, flight control of different modes and winglet's state and switching control of different flight modes and winglet modes. Specific research contents are as follows:Firstly, the nonlinear mathematical model of NMV has been built according to the domestic and abroad research data of NSV and the characteristics of variable winglets. Considering the complex characteristics of flight environment and differences of missions, atmospheric environment model and engine thrust model of different modes are established. Additionally, the open-loop characteristics of the NMV are analyzed, which lays the foundation for flight control and switch control study.Secondly, due to the large flight envelope of the NMV, there are many differences in different flight mode characteristics and control requirements. Therefore, the flight modes of NMV are divided based on the differences of missions and winglet states of NMV, and the mode constraint conditions and the influence to the aerodynamic force and moment of different winglet states are analyzed. Considering the advantages of sliding mode control method in dealing with the uncertainty and the disadvantage of chattering, double exponential reaching law sliding mode control method is put forward based on the equivalent model of feedback linearization, and then design the flight controller of climbing and cruise mode is designed. This paper theoretically proves the stability of double exponential reaching law, and then proves that this method is effective and robust by simulation.Thirdly, flight states will mutate during the mode switching which can result in the unsteadiness of the NMV. Therefore, in view of the switching process of climb/cruise modes of NMV, the control effects of direct switching are given which illustrates the necessity of the switching control. Considering good robustness of the sliding mode control method, one algorithm of double exponential reaching law sliding mode switching control algorithm based on inertial element is put forward. The advantages and disadvantages of this method compared with the traditional inertial element switch control method are elaborated through the simulation analysis.Finally, in view of the particularity of the research object, the influences of retracted winglets on flight control are studied in order to lay foundation for the control system of different winglet conditions. However, the change of winglet states leads to the change of aerodynamic parameters, so the double exponential reaching law sliding mode switching control algorithm based on inertial element is applied to the switching process. Digital simulation shows that this method has good control effects and strong robustness.To sum up, this thesis researches in flight control of different flight mode, flight mode switching control of different mode and winglet states changing control. As shown in the research achievements, the new switching control algorithm can not only get excellent control performance, but also ensure the smoothness and robustness of mode switching process.