Switched fixed-time observer-based distributed fault tolerant formation control for unmanned surface vehicles

This article investigates distributed robust fault-tolerant formation-tracking control for multiple unmanned surface vehicles under actuator saturation, actuator faults, and external disturbances. A hyperbolic-tangent function is introduced to approximate asymmetric actuator saturation, thereby transforming the formation-tracking problem for USVs with actuator faults and saturation into a known-direction variable-gain control problem. To address this variable-gain problem, a power-enhanced smooth analytic Nussbaum function is constructed. A switched fixed-time extended state observer is further developed to estimate lumped disturbances caused by actuator faults, saturation effects, and environmental perturbations. Comparative simulations with three representative recent fault-tolerant control methods, including adaptive fault-tolerant control, fixed-time fault-tolerant control, and adaptive RBFNN observer-based fault-tolerant control, show that the proposed method reduces the average attitude-error integral indices by approximately 16.1%, 10.4%, and 5.4%, respectively. Field experiments further validate the practical feasibility of the proposed strategy for multi-USV formation missions in complex marine environments.