Formation Control Method For Quadrotor Unmanned Aerial Vehicles

Nowadays, single quadrotor system cannot meet the requirements of the diversified tasks with its increasing manipulation complexity. Therefore multi-UAVs have been used on more and more missions, attracting wide attention at home and abroad. UAV formation flight control problem is a core research topic among multi-UAV system. In this paper, we propose a control framework which based on the leader-follower formation structure.Firstly, the mathematical description of quadrotor UAV formation flight problem is established. The UAV formation flight problem can be decomposed into two subproblems. One is a formation keeping problem, which determines the formation structure, the other is a UAV flight control problem, which can ensure tracking results of UAVs. Then, the UAV formation flying process can be decomposed into three steps. In the first step, the leader is designed to track its desired trajectory. In the second step, the follower maintains the formation structure according to the leader’s actual trajectory. And in the last step, the follower should track its desired speed command signal by using the same method with the leader.Secondly, we study the problem of maintaining UAVs’ formation stucuture, and design follower’s control algorithm to keep the formation. According to the UAVs’ relative kinematic model based on the leader-follower formation structure, we identify that the follower’s vertical position channel and its transverse/longitudinal position channel do not exist mutual coupling in formation flight. Then, formation keeping controllers can be designed respectively. For the vertical position channel, we design its PID controller directly, because the vertical channel is only related to the vertical speeds of the leader and follower. For the transverse/longitudinal position channel, the formation keeping controller is designed by using Backstepping method. Thus, follower’s desired speed command signal which aims to maintain the formation structure can be obtained. And we can convert the UAV formation flight problem to the single UAV control problem.Finally, we study the model characteristics of quadrotor, design its trajectory tracking controller. We analyze the coupling and under-actuating characteristics of the UAV, and establish a multi-loop control structure. We take the attitude loop as the inner loop, position loop as the outer loop. And we also obtain a four-channel structure, with height channel, yaw channel, pitch channel and roll channel respectively. Since each channel has a strict-feedback form, the integral Backstepping method can be used to design the UAV flight controller. By tracking the spiral trajectory signal, the validity of the flight controller based on integral Backstepping is verified. Numerical simulations on spiral and straight line also show that the control framework based on leader-follower formation structure can work effectively in UAV formation flight.