Research On Tracking Control Of Fixed-wing Vertical Take-off And Landing Aircraft

Vertical take-off and landing(VTOL)aircraft,with the unique advantages of a fixed-wing fighter and a helicopter,has immeasurable military strategic significance and civilan application value.Since its birth,it has been highly concerned by the world major military power,and has become a research hotspot in the field of aerospace.As the core technology of VTOL aircraft system,control technology is the key to ensure safe flight and complete flight missions.However,the complex body layout and volatile flight environment make the aircraft exhibit nonlinear,strong coupling,non-minimum phase and so on characterisics,which bring great challenges to the control system design.Therefore,we take the control problem of VTOL aircraft as the reaserach topic,and conduct indepth study,the main contents of this paper are as follows:Firstly,considering the trajectory tracking problem when input of system are affected with uncertain disturbances,a control strategy is presented which combines adaptive immersion and invariance(I&I)with sliding mode variable structure control.In order to overcome the adverse effect of input disturbances,an adaptive I&I disturbance estimation law is adopted to estimate input disturbance on line and disturbance estimation is used to compensate in the controller which enhances the stability and tracking accuracy of the system.By selecting an appropriate compensation function,the exponential convergence of disturbance error system can be guaranteed.Based on adaptive I&I disturbance estimate law and sliding mode control method,a robust tracking controller is designed,and then the stability of closed system is proved by Lyapunov stability theory.The final simulation results show that the proposed method can ensure the system output track the given reference trajectory quickly and stably in the presence of input disturbances.Secondly,aiming at the disturbance rejecting problem of trajectory tracking when input of system are affected with uncertain disturbances,a control strategy combining optimal control,nonlinear disturbance observer and sliding mode variable structure control is presented.In order to offset the adverse effect of input disturbances,a nonlinear disturbance observer is adopted to estimate input disturbance on line.By choosing the appropriate observer gain function,the exponential convergence of observation error system is guaranteed.On the basis of nonlinear disturbance observer,a robust controller is designed to enhance the stability of system and to effectively track the given desired trajectory in the presence of input disturbance.And then the stability of closed-loop system is proved by Lyapunov stability theory.The simulation results verify that the proposed scheme has better trajectory tracking precision and better rejection of disturbance.Thirdly,considering the fixed-point landing problem of VTOL aircraft,an image-based visual servo approach is presented.The binocular visual model is adopted,which does not need to obtain the depth information of unknown feature points,and the model has a low dimension and is easy to calculate.Using the airborne camera to obtain the image information,the visual servo controller is designed based on the backstepping method to guide the VTOL aircraft to land at desired position.Because the visual model does not contain depth information,the measurement or estimation of unknown depth information is avoided which which improve the performance of the system.And then Lyapunov theory is used to prove that the closed-loop system is asymptotically stable,and the image error converges to zero under the action of the proposed controller.Finally,aiming at the problem that it is difficult to measure partial state of VTOL aircraft in real time and accurately,an output feedback control scheme based on finite time observer is presented.To begin with,a finite time output feedback observer is designed to estimate the state which is difficult to measure in real time so as to reconstruct the full state feedback control system.Subsequently,based on the finite time observer,the state estimate is introduced into the controller for compensation,and then the output feedback controller is designed by the finite time control method.The stability demonstration and simulation results show the effectiveness of the proposed method.In a word,this paper makes an in-depth study on some key problems in the design of VTOL aircraft control system,and makes a positive theoretical explore for technical breakthroughs of control system design.