Modeling And Control Technology Research In Transition Phase Of Tilt Tri-rotor UAV

Tilt tri-rotor UAV(Unmanned Aerial Vehicle)contains the advantages of rotary and fixed-wing,the switching between these two modes can be achieved by the tilt of rotors,it has the ability to vertical take-off and landing,hover and fast forward movement.The change of structure not only brings many advantages but also some technical difficulties,especially for the flight control in transition mode which involves the design of optimal tilting path,rotor and rudder redundant power distribution,attitude stability and transition strategy and other issues.Basing on the flight platform designed by laboratory,further study is developed to analyze flight control and modeling technology in transition mode.An improved control scheme is proposed,addressing on balance the path of mode switch,flight characteristic analysis,establishment of control allocation schemes,design of tilt strategy,flight control system design and simulation,flight test verification and other technical problems.Specifically,the aspects mentioned above can be listed as follows:(1)Considering the dynamic characteristics of rotary and fixed-wing,nonlinear flight dynamic model of tilt tri-rotor UAV has been established.On the basis of geometric layout of platform and flight dynamic equation of fixed wing,measurements of the dynamic geometric layout and test of electric rotor tension and torque characteristics are completed,the dynamic model of rotor is obtained.System identification for the fixed-wing mode is carried out to get the coefficients of aerodynamic.Combining physical test and data to build the precise dynamic model of the whole aircraft.(2)Aiming at the ideal flight state of the tilting process,based on the static equilibrium equation of the body coordinate system,the optimal tilting path is designed.In transition mode,limited by the maximum of rotate speed,the front rotors tilt too fast or too slow are not conducive to stable flight.To ensure the stability of the transition flight,rotor thrust and aerodynamic must match each other reasonably to overcome the gravity and air resistance during flight,so the maximum control margin can be achieved.The relationship between tilting angle and airspeed is obtained by balancing the force equation and torque equation of the transition mode,and then using least square method to fit the optimal tilting path.(3)The design of the transition mode control distribution scheme is completed by analyzing the aerodynamic force of fixed wing and the thrust of rotor.Transition flight mode is a focus as well as a difficulty of the research in this paper.Aiming at the characteristics of the transition mode,two kinds of control schemes are proposed,which are consist of decoupling control algorithm and control allocation based on efficiency optimization.The first stage of the decoupling control which has low speed is controlled by rotors,and the second stage in high speed is controlled by rudders.The rotors and rudders are used together to control aircraft in the control allocation based on efficiency optimization,control weight is based on airspeed.By the simulation analysis,new algorithm enable to reduce the change of altitude in transition mode.(4)On the basis of the optimal tilting path,make use of control allocation scheme new designed,the switching strategy is developed and has reduced the change of attitude and altitude in the process of transition.The current strategy is not smooth enough,there is altitude change in transition flight,and continuous switch strategy is obtained based on the optimal tilting path.The PID controller and the auto disturbance rejection controller are established,on the basis of these two controllers,the different control effects and feasibility of switching strategy are analyzed,which points out the direction and lays the foundation for further research.