Leader–follower formation control of underactuated autonomous marine surface vehicles with limited torque

• A saturated leader–follower formation controller is proposed for surface vessels.
• A new second-order leader–follower formation model is introduced.
• Generalized saturation functions have been used to prevent actuators saturation.
• Uncertain nonlinearities are compensated by neural network and adaptive techniques.

This paper proposes a leader–follower formation tracking controller for underactuated autonomous marine surface vehicles with limited torque under environmental disturbances. A second-order formation dynamic model is developed in the actuated degrees of freedom of the followers to simplify the design procedure. Then, a formation tracking controller is designed by utilizing generalized saturation functions to reduce the risk of actuator saturation. Radial basis function neural network and adaptive robust control techniques are also adopted to preserve the controller robustness against unmodeled dynamics and environmental disturbances induced by waves and ocean currents. A Lyapunov-based stability analysis shows that all signals of the closed-loop system are bounded and tracking errors are semi-globally uniformly ultimately bounded. Finally, simulation results are provided for a group of surface vessels to illustrate the effectiveness of the proposed controller as a qualified candidate for real implementations in offshore applications.