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This article investigates the singularity avoidance adaptive output-feedback fixed-time consensus control problem for multiple autonomous underwater vehicles (AUVs) subject to nonlinearities. A distributed state observer is designed to reconstruct the unmeasurable coupling states of each AUV system.In order to handle the unknown nonlinearities of the multi-AUV systems, the fuzzy logic systems are adopted to approximate unknown hydrodynamic parameters. By combining adaptive fixed-time control with backstepping technology, an adaptive singularity avoidance fixed-time consensus control algorithm is developed, where a new error switching mechanism is designed for avoiding the singularity problem caused by the differentiation of the virtual control law. Subsequently, a singularity avoidance distributed adaptive output-feedback fixed-time fuzzy controller is presented, under which an auxiliary function is designed to handle the difficulty of the fixed-time stability analysis under the output-feedback control strategy, where two types of observer errors are needed in the designed Lyapunov function to achieve the fixed-time stability. Then, based on the fixed-time stability criterion, it is proved that both the consensus tracking performance and the closed-loop stability can be guaranteed in fixed time. Finally, a simulation example verifies the effectiveness of the developed control strategy.

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