Research On Automatic Landing Control Technologies For UAV Under Complex Conditions

As one of the most complex phases in whole flight process of wheeled UAV, landing has the characteristics of low airspeed, high angle of attack and low height, which require automatic landing control can not only precisely control the attitude of UAV, but also stabilize the aircraft on the scheduled trajectory, especially in the flare stage, all states of UAV must be maintained with high accuracy in order to make a safety touchdown. In recent years, with the improvement of the control technology, as well as the needs of UAV to develop in the multiple directions, the design of robustness automatic landing control laws which can work well under complex atmosphere conditions and flight states is becoming a crucial technique in UAVs'flight control fields.This thesis takes a high span-chord ratio UAV as the research plant, through the dynamics and kinetics analysis of this sample UAV, a six degree of freedom nonlinear mathematical model which incorporates contants value wind, gust, wind shear and turbulence model has been established. After researching on the influence of complex atmosphere conditions and different landing weight on flight performance of the sample UAV during landing phase, a landing trajectory composed of the decent phase and the flare phase trajectory is designed. Particularly, the flare phase is devided into two sub phases including exponent and straight pull-up sub phase for the safety landing. To meet the different requirements in various landing environment, airspeed controller is introduced to decouple flight path and airspeed during landing, meanwhile, a dual-loop feedback control structure which can improve the dynamic respone of the controller is applied to the altitude control to restrain the altitude tracking disturbances caused by external complex conditions.Through analyzing the impact of complex atmosphere conditions to lateral control, flight path tracking, decrab and deroll controller are designed. The decrab control is added to aligns the UAV's heading with the runway centerline.The deroll control is initiated close to the runway, its purpose is to limit roll command as the UAV reaches the runway to protect the wings tips prior to the touchdown.To test and verify the effectiveness of the automatic landing control under complex conditions, automatic landing simulations have been performed under the conditions of different landing weight of the UAV and various combinations of atmospheric disturbances, which manifest the validity of the control strategies and the correctness of the control laws under complex conditions.