Trajectory tracking control for an unmanned hexrotor with lumped disturbance

In recent years, unmanned aerial vehicles (UAVs) have experienced an important growth both in research activities and industrial field. With the abilities to take off, land vertically, and hover along with natural agility and controllability, a hexrotor can extend the potential roles of UAVs. From the view of mechanical structure, hexrotors can be considered simpler than the helicopters because they do not have the swash-plate and do not need to eliminate the gyroscopic torques created by the spinning motors. However, hexrotors are not only extremely sensitive to control inputs and disturbances, they are also complex systems that are nonlinear, highly unstable and with multiple input-multiple output (MIMO) and a high degree of coupling characteristics. This study proposes a hybrid control algorithm combined integral backstepping control with linear active disturbance rejection control to solve the problem of trajectory tracking control for an unmanned hexrotor with lumped disturbance. First, the nonlinear dynamical model of the hexrotor was deduced with the Newton-Euler equation, and the mathematic relation of the input and the output was analyzed. Second, the hexrotor system was divided into the position loop and the attitude loop according to the characteristic of the dynamical model. In the position loop, an integral backstepping control algorithm was applied to design the controller by introducing an integral term to improve the disturbance resistance and eliminate the static error of the trajectory tracking. In the attitude loop, a linear active disturbance rejection control algorithm was used to design the controller by introducing a linear extended state observer to estimate and compensate for the lumped disturbance. Lastly, the effectiveness of the proposed control algorithm was verified through two simulation cases and a flight experiment. The research results show that the proposed algorithm has a strong ability to resist the lumped disturbance and make the hexrotor quickly and steadily track the referenced trajectory. Hence, the algorithm has an important engineering application value.