Adaptive Harmonic Extended State Observer Based Anti-Swing Attitude Control of a Quadrotor-Slung-Load System

The presence of a slung-load during the flight of a quadrotor generates swing effects that can greatly influence the dynamics of the quadrotor. These effects have the potential to threaten the stability of the system’s attitude. This study presents a disturbance compensation strategy that is designed based on the utilization of an adaptive harmonic extended state observer (AHESO) in order to solve this problem and achieve precise attitude control. To derive the aforementioned algorithm, a comprehensive mathematical model for the quadrotor-slung-load system is built. The periodic features of disturbance are derived by considering the movement of the slung-load. Subsequently, by taking the periodic features of the disturbances into account, the AHESO for accurate disturbance estimation is designed. In this observer, an online frequency estimator for the harmonic disturbances is introduced. Lyapunov theory is introduced to examine the stability of the AHESO. In addition, backstepping-based approach is employed to design an attitude controller for accurate attitude tracking of the quadrotor. Analysis are conducted regarding of the entire stability of the quadrotor-slung-load system. In the end, the effectiveness of the designed method is verified by comparative simulations.