Research On Flight Control Design Under High Angle Of Attack Maneuvering For Agile Missiles

In order to improve the maneuverability of a tactical missile, the available range of the angle of attack should be increased, which leads to the concept of agile missile. This thesis focuses on the air-based agile missile equipped with Reaction-jet Control System(RCS). In accordance with the requirement for the high angle of attack control system during the agile turn, several aspects are investigated systematically, including high angle of attack control design, Bank-to-turn(BTT) control for agile turn, angle of attack command generation, measured value correction and attitude control for large angle maneuvering.Firstly, the mathematical model of the agile missile system is established. The aerodynamic characteristics at 90 ° angle of attack are simulated through the calculation of flow around a circular cylinder. Then the aerodynamic coefficient modeling is achieved by combining engineering prediction with artificial disturbance. On this basis, the equations of motion of the agile missile are established, during which the kinematical equations are rewritten by the quaternion algorithm to solve the singularity problem in the attitude description for large angle maneuvering.Secondly, the control design of the nonlinear system for the agile missile with a high angle of attack is addressed. An angle of attack controller based on Active Disturbance Rejection Control(ADRC) technique and fuzzy logic is proposed. Extended State Observer(ESO) is adopted to online estimate and compensate the total disturbance in the control system, which makes the disturbance rejection mechanism a reality. Additionally, the fuzzy logic is employed to achieve not only the adaptive adjustment of the feedback gain of state error, but the instruction dispatch of the RCS/Aero compound control. Eventually, the high angle of attack control of the agile missile is achieved with the serious uncertainties in the missile model. In numerical simulations, the proposed method, ESO approach and Pulse Width Pulse Frequency technique used in RCS control input modulation are verified feasible and effective for the agile turn control.Thirdly, two maneuvering approaches for three-dimensional agile turn are proposed and implemented by virtue of various Sliding Mode Control methods. For BTT strategy, the three channel control system is designed using ADRC method. Subsequently, to further improve the autopilot performance, an imporved Dynamic Surface Control(DSC) approach is proposed combining with ESO methodology, which makes the control system have better performance on convergence rate and steady state error. In addition, considering the practical implementation for the agile turn, a simplified BTT strategy is adopted. In accordance with the requirement for this strategy, an improved Nonsingular Terminal Sliding Mode(NTSM) controller is designed to achieve the stabilization control in the roll and yaw channels. Ultimately, different control approaches are compared and analyzed through numerical simulations, in which the superiority of the proposed methods is validated.Fourthly, two problems involved in engineering implementation of the angle of attack feedback control for agile turn are investigated. To solve the problem of the angle of attack command generation in terms of a guidance signal, the nonlinear characteristics of the turn rate dynamics are discussed at first, followed by the argumentation of the reversibility of this dynamics model. Then a method using neural network to approximate the inverse model of turn rate dynamics is proposed. On this base, the angle of attack command augmented by a variable structure technique is generated to correspond with the desired turn rate. After this the filtering correction of the measured value of the angle of attack and angle of sideslip is addressed. The filtering correction scheme based on Kalman filter is designed according to the characteristics of the missile dynamics. The linear Kalman filter is then adopted to calculate the optimal predicted values of the angle of attack and angle of sideslip. The simulation results demonstrate the feasibility of the proposed methods.Finally, in consideration of the objective difficulty for practical implementation of the angle of attack control, an approach to control the missile’s attitude is proposed while the agile turn is indirectly achieved. First, the traditional NTSM control method is developed for a class of second order uncertain nonlinear system. The improved NTSM with compound sliding surface is proposed to increase the convergence rate when the system is far from equilibrium state. Then the real time estimation of the system uncertainty provided by ESO is compensated in the control law, which attenuates the chattering in control input significantly. Eventually, the improved NTSM control is applied to the attitude control of agile turn successfully. Comparative study via numerical simulation validates the effectiveness and superiority of the new approach.