Fixed-time formation control for AUVs with unknown actuator faults based on lumped disturbance observer

This paper investigates the adaptive fixed-time formation control for multi-AUV systems (MASs) in the presence of model uncertainties, ocean current disturbances and unknown actuator faults . In order to improve the robustness of the system, an adaptive fixed-time integral sliding mode disturbance observer (AFISMDO) is designed to estimate the lumped disturbance composed of model uncertainties, ocean current disturbances and unknown actuator faults. Based on the designed observer, an adaptive fixed-time fault-tolerant controller (AFTFTC) is designed by combining nonlinear command filter and backstepping technique which can ensure that the trajectory tracking errors of the follower AUVs and the corresponding virtual leader AUVs converge to the origin within a fixed time, so as to achieve the purpose of formation. Compared with the traditional finite-time control, the convergence time for the closed-loop system is independent of the initial state . Finally, the simulation results show that the proposed control algorithm has superior control performance. • A novel AFISMDO is proposed to estimate the model uncertainty and external ocean current disturbance and compensate the unknown actuator faults. The AFISMDO can estimate the disturbance upper bound without assuming that the disturbance is known and the observer error can converge in a fixed time. • A nonlinear command filter is used to overcome the excessive calculation problem caused by the backstepping method, and the compensation signals is designed to reduce the filtering errors. • Based on the backstepping technique, an AFTFTC is designed to ensure that the follower AUVs can accurately track the trajectory of the virtual leader AUVs within a fixed time, and the convergence time is only related to the design parameters of the controller.