Research On Control Methods For Trajectory Tracking Of Air-Breathing Hypersonic Vehicles

Air-breathing hypersonic vehicles(AHVs)have attracted lots of attentions for years due to its outstanding values in both military and civilian applications.As one of the key AHV techniques,the flight control designing also has become one of the most interesting and advanced issues all over the world.Because of strong nonlinearity,coupling,uncertainty and fast time-varying,flight control for AHVs is still a challenging task.For the velocity and altitude tracking issues in cruising flight,a coupled model of AHVs is constructed based on the interation configuration of X-43 A.Futhermore,through control-oriented model simplification,the tracking control problem of AHVs is translated into the control issue of nonlinear system with mismatched system disturbance.Therefore,considering the tracking control problem of a flexible air-breathing hypersonic vehicle(FAHV)in cruise flight,this paper takes the system disturbance rejection as the main thread and provides indirect and direct approaches for system disturbances rejection respectively.Firstly,for the case of small system disturbances,three types of indirect approach is proposed to reject system disturbance,as the control design based on stochastic robust analysis(SRA),higher-order sliding mode control(HOSMC),and the composite control based on fractional-order sliding mode control(FOSMC).Simulation results illustrate that the indirect approaches could satisfy the requirements of AHVs tracking control problems with light system disturbance due to their inherent robustness.Secondly,for the case of strong system disturbances,two types of direct approach are proposed to reject system disturbance,as the control design based on uncertainty and disturbance estimator(UDE)and the disturbance decoupling control(DDC).Simulation results show that due to direct observations of the system disturbance,the direct approaches could deal with the tracking control issue of AHVs with strong system disturbances,as all of the aerodynamical coefficients have a vibration of ±30% with respect to the nominal value.The contributions of this work can be summarized as follows:1)Due to nonlinearity,coupling,and parameter uncertainties of longitudinal modes of AHVs,strong robust and high accuracy controllers are required.The traditional control strategy based on SRA is improved.In order to overcome the early convergence and weak searching ability of traditional genetic algorithm,a novel hybrid particle swarm optimization algorithm is proposed to search the best control parameters of linear quadratic regulator.While,a novel parameter determination strategy is proposed for the control parameter selection of HOSMC.The proposed parameter determination strategy provides a newly and feasible set of control parameters for HOSMC.2)In order to avoid relying on precise model of AHVs,a novel composite FOSMC strategy is proposed based on linear quadratic optimal theory.The control strategy proposed is composed of two parts,as continuous control law and discontinuous control law.The continuous law is designed based on LQR,which guarantees the fast convergence speed.While the discontinuous law is design based on FOSMC,which is used to depress the inertial uncertainties and external disturbances and guarantee the system robustness.3)For the case of strong system disturbances,a new UDE-based control stratery is proposed based on the concept of back-stepping design.The longitudinal dynamics of AHVs is rewritten as the forms of closure loop with lumped uncertainty and disturbance.Then UDE is employed to estimate the system disturbance and compensate the baseline controller.