Unmanned aerial vehicle (UAV) with slung load system is a classic air transportation system. In practical applications, the suspension point of the slung load does not always align with the center of mass (CoM) of the UAV due to mission requirements or mechanical interference. This offset creates coupling in the system's nonlinear dynamics which leads to a complicated motion control problem. In existing research, modeling of the system are performed about the UAV's CoM. In this work we use the point of suspension instead. Based on the new model, a cascade control strategy is developed. In the middle-loop controller, the acceleration of the suspension point is used to regulate the swing angle of the slung load without the need for considering the coupling between the slung load and the UAV. Using the off-center reference frame, an inner-loop controller is designed to track the UAV's attitude without the need of simplification on the coupling effects. We prove local exponential stability of the closed-loop using Lyapunov approach. Finally, simulations and experiments are conducted to validate the proposed control system.

翻译：带吊挂载荷的无人机系统是一种经典的空中运输系统。在实际应用中，由于任务需求或机械干涉，吊挂载荷的悬挂点并不总是与无人机的质心重合。这种偏移在系统的非线性动力学中引入了耦合，导致了一个复杂的运动控制问题。在现有研究中，系统的建模通常是围绕无人机的质心进行的。在本工作中，我们改用悬挂点作为建模基准。基于新模型，我们提出了一种级联控制策略。在中环控制器中，利用悬挂点的加速度来调节吊挂载荷的摆角，而无需考虑吊挂载荷与无人机之间的耦合。使用偏心参考系，设计了内环控制器来跟踪无人机的姿态，且无需对耦合效应进行简化处理。我们利用李雅普诺夫方法证明了闭环系统的局部指数稳定性。最后，通过仿真和实验对所提出的控制系统进行了验证。