Formation Control Of Ouadrotors With Unknown Mass And Its Application In Agricultural Field

The quadrotor UAV has been widely applied in multiple occasions due to its structure simplicity,ability to vertical take-off and landing,easy maintenance and usage.However,as the mission requirements continue to increase,the control requirements for single drones are also rapidly increasing.The cooperative formation of UAVs has received more attention and research because of its low requirements for individual drones,large operating areas and high efficiency.In this paper,the UAV formation is implemented to the agricultural plant protection problem,quadrotor flight and formation control researches are carried out with pesticide spraying as the main scenario.The main work and contributions are as follows:(1)Dynamic analysis under the experimental platform of quadrotor UAV is performed in order to obtain the physical model under small angle or hovering state.Considering the real-time changes of the total mass of UAV and load in the pesticide spraying scenario,the total mass is adaptively estimated.The backstepping method and the fractional cascade PID control are applied to the position loop and attitude loop control respectively.The Matlab simulation results show that the adaptive method can track the true value quickly and accurately regardless of the step change or high-order change of the total mass.The comparison with the traditional PID control algorithm illustrates that the proposed algorithm is more stable under height control,it has obvious advantages in trajectory tracking,and excellent performances in terms of stability time,overshoot and static error.(2)After doing research on various methods of formation control,this paper proposes a virtual structure method with coupling terms,combined with behavior method.At the same time,optimal concept has been used in balancing the relationship among autonomous obstacle avoidance,formation maintenance and mission completion.Firstly,the paper analyzes the stability of the virtual structure method with coupling terms.And then the method has been verified on Matlab platform,the simulation result demonstrates the proposed method can effectively reduce the influence of external disturbance on the flight path of individual UAVs,and under the obstacle avoidance condition,the virtual structure method with coupling can make quadrotors maintain the formation more precisely and complete the mission target better.(3)The pesticide spraying scenario can be considered as an application under the regional coverage problem.After studying a number of literatures on regional coverage problems,this paper proposes a "Z" shape formation method with multiple UAVs.By comparing the method with that in relevant literature,the algorithm has advantages in terms of efficiency,electricity saving and medicine reducing.Although the rectangular area is taken as an example,the algorithm can be generalized to the polygon area coverage problem based on the principle of "minimum width".Before the UAV formation flight,considering the different starting points of the UAV,this paper proposes a rendezvous algorithm based on Dubins curve,to get the best path with the least energy consumption and the same arriving time.Based on the above analysis and simulation experiments,the proposed algorithm provides a solution for the pesticide spraying scenario under the agricultural plant protection problem.The algorithm has small calculation amount and simple control structure,which provides more possibilities for engineering realization.At the same time,the formation rendezvous and formation control algorithms can also be used in other regional coverage problems such as regional demining,inspection,and map drawing;the control of quadrotor with unknown mass improves its performance and utility.