Control of Underactuated Autonomous Underwater Vehicles With Input Saturation Based on Passivity Using Feedback Concavification

This paper proposes a concept of feedback con-cavification to the control of an underactuated autonomous underwater vehicle (AUV) with 6-DOF, subject to actuator saturation, to improve transient performance and robustness, taking into account the presence of unknown model dynamics and disturbances. To address the underactuated problem under the dissipation framework, Euclidean geometry is utilized to match the dimensions of the input and output. Therefore, an interconnected architecture for the AUV system is proposed, enabling the AUV system to be transformed into interconnected passive systems via feedback within this architecture with guaranteed asymptotic stability. The concave passivity is then applied to the interconnected passive systems to handle uncertainties, disturbances, and actuator saturation problems. The proposed method with assigned concavity is effective in different scenarios with fast transient response and the decreasing
$L_2$
-gain under actuator saturation. Numerical simulations have demonstrated the effectiveness of the proposed interconnected passive architecture and the feedback concavification approach in improving the control performance of the underactuated AUV.