Research On Control Methods For Tracking Problem Of A Flexible Hypersonic Vehicle

Currently, the research of hypersonic vehicles has drawn more and moreattention through the whole world, and becomes a main area of near space flighttechnology, due to its significant value in both military and civil affairs. It makes thecontroller design of hypersonic vehicles highly challenging that it features fast-timevariations, system nonlinearities, coupling effects, uncertainties, flexible effects. Inorder to develop a stable tracking controller, the dissertation is extended progressivelyfrom system nonlinearities, parameter uncertainties, external disturbances, controlinput constraint, and actuator faults. The research issues include the high order slidingmode (HOSM) control method and finite-time stability theory in the flight trackingcontrol for the hypersonic vehicle.Firstly, a rigid-body model is established base on Newton’s laws of motion andEuler’s laws of motion. The elastic vibration equation is established with theassumption that the fuselage structure is a uniform free-free beam, analyzing thecouplings between the rigid and flexible dynamic mode. In order to overcome theflexible effects, system nonlinearities, coupling effects of hypersonic vehicles, asimplified model for controller design based on dynamic inversion technology isconstructed. Qusi-continuous HOSM controller is designed to deal with uncertainties,the upper bounds of which are known in prior. Homogeneous geometry ensures thatthe system states achieve finite time tracking performance with regard to referencecommands. Simulation results show that the proposed method assures robustness,finite time stabilization with respect to parameter uncertainties.Secondly, a novel adaptive HOSM control method, which can be recognizedfrom homogeneous geometry and integral sliding mode control theory, is proposedwhere the upper bounds of uncertainties are not required to be known in advance. Thecontroller contains two parts: one part is continuous nominal controller which isobtained using homogeneous properties, to stabilize the system in finite time withoutuncertainties; the other part is discontinuous controller which rejects boundeduncertainties. Meanwhile, the adaptive update law is designed base on sliding modesurface for estimating the uncertainties’ upper bound on line. The finite time stabilityof the control system is ensured using the Lyapunov stability theorem. Simulationresults are presented to illustrate the robustness of the control strategies.Thirdly, the robust control problem of parameter uncertainties, external disturbances, and control constrains for a flexible hypersonic vehicle (FHV) isinvestigated. The HOSM disturbance observer technique is applied to estimate thedisturbances in order to compensate the controller and disturbance suppression, wheredisturbance observer and controller synthesis design is obtained. The finite timestability of the system is analyzed by Lyapunov stability theorem. Simulation resultsverify the expected robust tracking performance of the proposed method. Comparedwith the adaptive sliding mode control method, the synthesis design strategy can dealwith the uncertainties, external disturbances, and control input constraint much better.Finally, an adaptive sliding mode fault tolerant control (FTC) method is proposedto deal with the loss of effectiveness in the actuators of FHV. A faulty uncertain modelof FHV is developed based on the known structure of the loss of effectiveness faults.The adaptive sliding mode FTC law is proposed to deal with the actuator faults timelyand quickly. An integral sliding mode surface, where an adaptive law is triggered toachieve the on-line computing of the control gain, is designed to detect the faults bythe unexpected increasing of the integral sliding surface. The finite time stability ofthe system is proved by Lyapunov stability theorem. Simulations results show therobustness and fault tolerant performance of the proposed method.