A Hierarchical Control Scheme for Formation Transportation of Multiple Quadrotors With Propeller Speed Constraints

The cooperative formation transportation technology of multiple quadrotors has attracted widespread attention in recent years due to its high fault tolerance and remarkable flexibility. This paper proposes a hierarchical control scheme for multiple quadrotors subject to propeller speed constraints and external disturbances to achieve cooperative formation transportation. The design of the proposed scheme primarily consists of developing a distributed coordinator and some tracking controllers. In the distributed coordinator, position coordinators generate the desired positions for all quadrotors with payload using information such as the position and velocity of a virtual leader. This is followed by differential flatness-based trajectory planners, which further derive the desired offset-free trajectories. The tracking controllers combine the nonlinear model predictive control, angular velocity control, and a propeller speed allocation algorithm to generate appropriate propeller speed commands for all quadrotors with payload, ensuring accurate trajectory tracking. Under the proposed scheme, multiple quadrotors with payload maintain the desired formation while tracking the virtual leader, thereby achieving cooperative formation transportation. Notably, when the position coordinators are omitted, the scheme simplifies to a single-quadrotor trajectory tracking controller. Numerical simulation results, including both single-quadrotor trajectory tracking and multiple quadrotors cooperative transportation scenarios, demonstrate the effectiveness of the proposed scheme. Specifically, it achieves remarkable tracking performance in single-quadrotor operations, while enabling cooperative formation transportation in multiple quadrotors systems.