3D hybrid formation control of an underwater robot swarm: Switching topologies, unmeasurable velocities, and system constraints

This paper addresses formation control of underactuated autonomous underwater vehicles in three-dimensional space, using a hybrid protocol that combines aspects of centralized and decentralized control with constraints that are particular to underwater vehicles, including switching topologies, unmeasurable velocities, and system constraints. Using a distributed leader-follower model, the hybrid formation protocol does not require velocity sensing, access to global information, or static and connected topologies. To handle switching jointly connected networks-that is, to tolerate temporary disconnections-a distributed observer is designed for followers to cooperatively estimate leader states using local measurements and local interactions. On this basis, a compound formation control strategy is proposed to achieve geometric convergence. Firstly, cascaded extended state observers are developed to recover the unmeasurable velocities and unknown dynamic uncertainties induced by internal model uncertainty and external disturbances. Secondly, an improved three-dimensional line-of-sight guidance law at the kinematic level is used to address the underactuated configuration and the nonzero attack and sideslip angles. Thirdly, to overcome potential instability as a result of system constraints, including velocity constraints and input saturations, two adaptive compensators in the dynamic controller are used to address the negative effects of truncation. Using the proposed approach, the estimation errors and formation tracking errors are proved to be uniformly and ultimately bounded. Additionally, the numerical simulation results verify the performance of the approach and demonstrate improvement over both distributed and centralized state-of-the-art approaches.(c) 2022 ISA. Published by Elsevier Ltd. All rights reserved.

Automated summary

This paper proposes a hybrid formation control protocol for underactuated autonomous underwater vehicles in three-dimensional space. The protocol incorporates aspects of centralized and decentralized control and considers specific constraints related to underwater vehicles. A distributed leader-follower model is used, eliminating the need for velocity sensing, global information access, or static and connected topologies. The approach handles switching topologies and utilizes a distributed observer for followers to estimate leader states cooperatively. The compound formation control strategy includes extended state observers, three-dimensional line-of-sight guidance, and adaptive compensators to address system constraints. Simulation results demonstrate the effectiveness of the proposed approach compared to distributed and centralized approaches.