Research On Modeling And Advanced Flight Control Theories For Hypersonic Vehicle

The dynamic characteristics of the hypersonic aircrafts will vary considerably over the flight envelop than other aircrafts due to their extremely wide range of operating conditions and rapid change of mass distributions. Furthermore, because of airframe-integrated scramjet utilized and the flight conditions of high altitudes and Mach numbers, hypersonic aircrafts are very sensitive to changes in atmospheric conditions. Moreover, many aerodynamic and propulsion characteristics still remain uncertain and are hard to predict due to the effect of the structural dynamics, propulsion aerodynamics and coupling between them. As a result, the hypersonic vehicle model is uncertain, multivariable, unstable, and possesses significant input-output cross-coupling. Therefore, it is essential to design flight controllers with high non-linear control ability and robustness for hypersonic aircrafts.In order to grasp the hypersonic vehicle models complex dynamic characteristics, the differential equations of the hypersonic vehicle model including rigid and elastic modes are established. The simulation tool is used to calculate the aerodynamic coefficients and eigenvalues in the longitudinal and lateral motion modes, and compute the flight trim points in the different flight velocities and altitudes, then approximately get fight envelope of the whole flight process. By analyzing the results obtained above, the dynamic characteristics and flight specialty of hypersonic vehicle can be understood. Furthermore, it is possible to provide appropriate objects to design flight control systems for hypersonic vehicle.Aiming to highly nonlinear and tight coupling mathematic model of hypersonic vehicle, the theory of feedback linearization introduced can convert accurately nonlinear mathematic model into equivalent linear model for control design. By the proper transformation, dynamic inversion flight control systems for hypersonic vehicle designed can stabilize the system and relieve the coupling effects.For matching uncertain control problem for hypersonic vehicle, a dynamic inversion control method based on variable structure theory is proposed. This method combines the nonlinear decoupling ability of inversion control with the strong robustness of variable structure theory very well, and can be used to design controller to resolve a class of parameter and structure matching uncertainty control problems for hypersonic vehicle For mismatching uncertain control problem for hypersonic vehicle, an adaptive backstepping scheme and a variable structure control method based on backstepping respectively is introduced to resolve parametric mismatching uncertainties and nonparametric mismatching uncertainties control problem. And the hypersonic vehicle flight control system designed applies nonlinear dynamics inverse control as control inner-loop which can relieve the coupled multivariable relations, then adopts an adaptive backstepping scheme or a variable structure control method based on backstepping as control out-loop in order to guarantee global stability of the system and attenuate the effects of mismatching uncertainty.Considering the partially or completely unknown model dynamic for hypersonic vehicle, an adaptive dynamic inversion control method with the compensation and an adaptive control method based on function approximation are presented. The former can compensate the hypersonic vehicle model errors by the neural network output adjusted on line. And the latter approximates the unknown hypersonic vehicle model dynamics by one hidden layer neuron or fuzzy logic systems, then applies Lyapunov method which can attenuate the effects of both the external disturbances and the approximation errors to expected level.Aiming to unknown model dynamic and rank for hypersonic vehicle, total energy control theory studied applies the thrust of engine and the elevator controls and adjusts the change and the distribution of the total energy respectively, and the goal about changing and assigning the energy reasonably can be achieved, which will ensure the good nonlinear decoupling ability and the strong robustness for hypersonic vehicle. Furthermore, in order to increase control precision, the fuzzy logic control is combined with the total energy control theory adopted to design the fuzzy rules.The conclusion and perspective are given in the end of the paper.