Anti-Swing Control for Quadrotor with Slung Load Using Integral Backstepping Sliding Mode Controller and Extended State Observer

The quadrotor suspended load system is a typical underactuated, multivariable nonlinear system. Considering the presence of unknown time-varying disturbances in practical quadrotor suspended load systems and limited input conditions, ensuring precise tracking of the quadrotor along the desired trajectory and simultaneously achieving accurate tracking of the load's swing and trajectory pose significant challenges. Therefore, based on the characteristics of traditional quadrotor dynamics and kinematics systems, a coupled mathematical model for a quadrotor hanging load is reestablished. To address the limitations of the disturbance rejection capability and prolonged response time in the quadrotor suspended load system under certain disturbances when using the BS backstepping method controller, an Integral Backstepping Sliding Mode Controller (IBSMC) based on Extended State Observer (ESO) disturbance compensation is designed. This controller accurately tracks the nonlinear dynamics of the quadrotor suspended load system, improving its robustness, stability, and shortening the response time. The ESO observer designed based on the pendulum angle rate can address the issue of difficult sensor measurement of the pendulum angle rate state in practical quadrotor load systems, providing an estimate for this state. Finally, experiments are conducted in three-dimensional space, simulating trajectory tracking of the quadrotor suspended load system based on the BS backstepping method control, SMC sliding mode control, and the ESO-IBSMC controller proposed in this paper. Comparative experiments validate that the Integral Backstepping Sliding Mode Controller based on Extended State Observer disturbance compensation exhibits better performance metrics in trajectory tracking for the quadrotor suspended load system. The experiments also confirm that the ESO observer can effectively measure the pendulum angle rate state.