Research on Control of Quadcopter Suspension System Based on Differential Flatness Theory and Back-stepping Sliding Mode Control

Quadcopter UAV elastic suspension system has a good development prospect due to its flexible and easy-to-operate features. However, during the flight transportation process, the oscillation of load, the irregular extension of elastic ropes, and the oscillation of UAV may lead to safety problems such as UAV crashes. In order to solve the above problems, this paper introduces a quadcopter transportation system with a suspended load with highly elastic ropes and establishes a dynamic model of the system. In this paper, the model is first transformed by differential flatness theory to establish the corresponding control variable order, and then the virtual control variables are introduced to control the swing angle and rope length by using back-stepping and sliding mode control methods, so as to achieve the purpose of swing reduction while controlling the position of the UAV. The stability of system is demonstrated using the Lyapunov method. Numerical simulation results show that the proposed control method can enable the system to reach the specified position rapidly, the swing of load can converge quickly, and the rope length can be stabilized swiftly, which avoids the occurrence of flight accidents.