Abstract: In this paper, a cooperative control strategy that integrates Improved Prescribed Performance Control (IPPC), Integral Backstepping Sliding Mode Control (IBSMC), and an Extended Disturbance Observer (EDO) is proposed to address the stable control problem of a multi-UAV cooperative slung-load system subject to internal state constraints, such as actuator faults, input saturation, and varying payload mass, as well as external disturbances including wind field effects and downwash airflow. First, the Udwadia–Kalaba equation is employed to establish the constrained dynamic model of the multi-UAV cooperative slung-load system, accurately capturing the coupling relationship between the quadrotors and the slung-load. Then, based on graph theory, the slung-load is regarded as a virtual leader, and the desired trajectories of each quadrotor are generated to ensure spatial consistency and coordination of the system. Meanwhile, an improved prescribed performance control strategy is introduced to dynamically constrain the system error within predefined bounds, effectively preventing inter-quadrotor collisions and maintaining formation stability. Furthermore, an integral backstepping sliding mode controller is designed and combined with the EDO to achieve online estimation and compensation of model uncertainties and external disturbances, thereby enhancing the system’s robustness and disturbance rejection capability. Finally, Lyapunov-based stability analysis rigorously proves the global stability of the proposed control strategy, and simulation results demonstrate its superior tracking accuracy and cooperative performance under actuator faults, input saturation, and wind field disturbances.

Key words: Multi-UAV, cooperative slung-load, prescribed performance control, integral backstepping sliding mode control, extended disturbance observer