Robust fixed-time formation control for quadrotor unmanned aerial vehicles with directed topology

Formation control is one of the key technologies for multiple unmanned aerial vehicles (UAVs). Compared with asymptotic or finite-time controllers, fixed-time controller can provide a guaranteed settling time, which does not depend on initial conditions and is an appealing property for controller design. Thus, robust fixed-time formation controller design for quadrotor UAVs under external disturbance and directed topology is investigated in this paper. A multi-variable super-twisting like integral sliding mode surface and a disturbance observer are respectively designed for position and attitude loops to guarantee robustness. Bi-limit homogeneity is utilized to design the whole closed-loop fixed-time controllers. By skillfully using bi-limit homogeneity technique and Lyapunov theory, the comprehensive stability of position and attitude loops is addressed. Finally, the multiple UAVs are utilized to track a pre-planned trajectory in 3D space and simulation results illustrate that the settling time can be reduced about 40% compared with finite-time controllers.