Robust fault-tolerant control for underactuated takeoff and landing UAVs

This article surveys the trajectory tracking issue of underactuated vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAVs) subject to thrust and torque faults, i.e., loss of efficiency and actuator biases. In particular, a robust control algorithm against time-varying faults and disturbances is proposed. To exploit the underactuated nature of the VTOL UAV system, the control algorithm is developed based on a hierarchical framework, under which the position and attitude loops are studied in sequence. Specifically, by implementing a novel robust fault-tolerant control strategy, a force command is first synthesized for the position tracking to the desired trajectory, and then, a desired torque using an innovative sliding manifold is designed such that the nonsingular attitude tracking to an attitude command is achieved. This attitude command, as well as the desired thrust, is extracted from the synthesized force command. In terms of hierarchical system stability theory, it is shown that the overall closed-loop error system is asymptotically stable. Finally, simulation results validate and highlight the tracking performance of the proposed control algorithm.