A Distributed Framework Design for Formation Control of Under-actuated USVs in the Presence of Environmental Disturbances Using Terminal Sliding Mode Control

This paper proposes a distributed framework for formation control of USVs around a predefined target. This framework, according to the mission and problem conditions, includes three parts: determination of a desired path for each USV, preventing USVs entry to the target area and tracking the desired path of USVs under environmental disturbances. In the first part, a distributed approach is proposed to determine desired path for each USV and forming an aimed USVs arrangement around the target. In the second part, by modifying artificial potential function and smoothly redirecting USVs, the restriction of not entering the target’s region is met. Finally, in the third section, a robust control algorithm for the USVs navigation in the presence of wind and sea current disturbances is developed based on the nonsingular terminal sliding mode control. The developed control algorithm firstly improves maneuverability of USVs using virtual velocity command planning, and secondly, provides a finite time trajectory tracking. Also, stability of the closed loop control is analyzed using Lyapunov stability theorem and the performance of the proposed control algorithm is compared with results of the conventional terminal sliding mode control. Simulation results demonstrate proper performance of the proposed framework in terms of improving tracking accuracy of the desired path and reaching a circular arrangement of USVs surrounding the target.