Modified Super-Twisting Sliding Mode Control for Trajectory Tracking of a Cargo Quadrotor

Quadrotor Uncrewed Aerial Vehicles (UAVs) face several limitations, such as restricted flight time and vulnerability to disturbances, and require control algorithms able to handle complex and underactuated dynamics. Their control is even more challenging when a payload is carried. This paper addresses the trajectory tracking problem of a quadrotor UAV, which operates as a cargo drone transporting cable-suspended payloads. First, we derive a model of the cargo drone in matrix form. The payload is treated as a rigid body and the gyroscopic effects of the propellers are included in the formulation. Then, we design second order sliding mode controllers, using the Modified Super-Twisting Algorithm. The hierarchical control scheme consists of an outer position control loop and an inner attitude control loop. The coefficients of the sliding surfaces and the reaching laws are calculated via Lyapunov analysis, ensuring finite time convergence to zero of both sliding surfaces and their first order derivatives. The performance of the proposed controller is examined in simulations of a UAV carrying a payload while tracking a circular trajectory. In the simulation case studied, the integral of time multiplied by the absolute value of the tracking error is an average of about 70% lower for the proposed second order sliding mode controller than it is for the first order sliding mode comparison controller.