An Enhanced Energy Coupling-Based Control Method for Quadrotor UAV Suspended Payload with Variable Rope Length

The quadrotor suspended payload systems have difficulties to achieve precise positioning of the quadrotor UAV and suppression of the load swing angle at the same time because of their characteristics, such as underactuated, strongly coupling, nonlinear and so on. An enhanced coupling anti-swing controller is proposed to solve these problems. With analysis on the relationship between the displacement of quadrotor UAV and the payload swing angle, the three-dimensional dynamic variable rope length model of a quadrotor UAV based on Euler–Lagrange equation is built. An anti-swing method based on energy coupling is designed for this system to realize positioning and eliminate the problem of residual load swing. A new auxiliary signal function is constructed to enhance the coupling relationship between UAV position and load position. The control strategy of three-dimensional quadrotor UAV is designed based on the signal function by the Lyapunov stability theory. The stability of this system is proved by the Lyapunov method and the Barbalat's Lemma. With the experiment, the proposed method is compared with different control methods, the results show that the proposed method can realize the accurate positioning of the quadrotor UAV more quickly and restrain the load swing more effectively. It has strong robustness and stability after the system is added to the disturbance.