Robust Cooperative Control of Quadrotor Cooperative Transportation System via Time-Varying Disturbance Estimatio

Controlling a cooperative transportation system transporting a cable-suspended payload is challenging due to highly coupled dynamics and unpredictable disturbances. In this paper, a novel time-varying uncertainty and disturbance estimator (TV-UDE) is introduced to estimate and compensate for disturbances in real time dynamically. Unlike conventional fixed-gain UDE observers, the proposed TV-UDE method smoothly adjusts its gain over time: starting large to mitigate transient spikes and increasing to a small gain for accurate steady-state disturbance rejection. This strategy enhances robustness and stability by avoiding the peaking phenomenon associated with high-gain estimators. The asymptotic stability of the overall system is proved by the Lyapunov method. Finally, the feasibility of the proposed methodology is demonstrated through simulations.