Research On Nonlinear Adaptive Control Method Based On Backstepping For Air-breathing Hypersonic Vehicle

Hypersonic vehicle has unique characteristics, such as rapidity and large flightboundary. Therefore, it has great perspective in military and civil area. Despite of that,because of the multiple variables, nonlinearity, heavy coupling and uncertaintyfeatures, there are tough difficulties in the design of flight control system. Based onthe velocity and altitude tracking control problem of hypersonic vehicle under abovemodel characteristics, three aspects of work are discussed in this dissertation.According to the multiple variables, nonlinearity and uncertainty problems ofhypersonic vehicle, a generalized adaptive backstepping method is introduced torealize the stable tracking of velocity and altitude reference trajectory. For the altitudesubsystem, the flight-path angle, attack angle and elevator deflection are used as thecontrol variable of altitude, flight-path and attack angle respectively to ensure theconvergence of altitude tracking error; for the velocity subsystem, a dynamic inversemethod is designed. Meanwhile, five adaptive update laws are designed to onlineestimate the uncertain aerodynamic parameters. To solve the differential explosionproblem in the design procedure of backstepping method, three integrating filters areintroduced to avoid the differentiation of virtual control variables. The design ofcontrol method is based on Lyapunov function to ensure the global system stability.According to the immeasurability or inaccuracy measurement problem in theattack angle and flight-path angle, based on the generalized adaptive backsteppingcontroller, two sliding mode observers are designed to online estimate the unknownstate variables. In the sliding mode observer, the measurable altitude and pitch rate areused to online estimate the immeasurable flight-path angle and attack angle. Thesigmoid function is used to avoid chatter phenomenon of slide mode method. At last,the attack angle and flight path’s observer states are used to replace real states torealize the designing of generalized adaptive backstepping controller, and the stabilityof whole system is proved based on Lyapunov function.To solve the non-minimum phase problem caused by the coupling between liftforce and elevator control surface in the dynamic of flight path angel, a nonlinearequivalent control method based on interconnected subsystems is introduced to designvelocity and altitude stable tracking controller. For velocity tracking subsystem, a dynamic inverse controller is designed; for the altitude tracking subsystem, it isdivided into altitude-flight-path angle and attack angle-pitch rate subsystems, thenvirtual control inputs of flight-path angle and attack angle are designed respectively,the elevator and canard deflection are designed as linear equivalent control vector, andthe coordinate transformation is used into the system. In this way, the two subsystemsconstitute an input state stable and small gain stable interconnected system, so theconvergence of altitude tracking error is realized.Simulation analysis of flexible hypersonic vehicle is used to test and verify thevalidity of the designed controllers in this dissertation.