Nonlinear Model Predictive Control for Enhanced Navigation of Autonomous Surface Vessels

Abstract

This article proposes an approach for collision avoidance, path following, and anti-grounding of autonomous surface vessels under consideration of environmental forces based on Nonlinear Model Predictive Control (NMPC). Artificial Potential Fields (APFs) set the foundation for the cost function of the optimal control problem in terms of collision avoidance and anti-grounding. Depending on the risk of a collision given by the resulting force of the APFs, the controller optimizes regarding an adapted heading and travel speed by additionally following a desired path. For this purpose, nonlinear vessel dynamics are used for the NMPC. To extend the situational awareness concerning environmental disturbances impacted by wind, waves, and sea currents, a nonlinear disturbance observer is coupled to the entire NMPC scheme, allowing for the correction of an incorrect vessel motion due to external forces. In addition, the most essential rules according to the Convention on the International Regulations for Preventing Collisions at Sea (COLREGs) are considered. The results of the simulations show that the proposed framework can control an autonomous surface vessel under various challenging scenarios, including environmental disturbances, to avoid collisions and follow desired paths.

Figures (6)

• Figure 1: Observed disturbances $\boldsymbol{\hat{\tau}}_d$ in comparison to the simulated disturbances $\boldsymbol{\tau}_d$ with a model parameter deviation of 5% concerning the ground truth.
• Figure 2: Vessel states (surge, sway, and yaw rate) during a crossing give-way scenario followed by anti-grounding under the impact of environmental disturbances and model uncertainties. The speed plan in surge outside a critical region was set to $\unit[7]{\frac{m}{s}}$. It can be seen how the controller slows down in proximity to a dynamic obstacle $\unit[100]{s}<t<\unit[200]{s}$, and in proximity to grounding hazards $\unit[300]{s}<t<\unit[500]{s}$.
• Figure 3: Distance to grounding hazards and dynamic obstacles regarding a crossing give-way scenario under the impact of environmental disturbances.
• Figure 4: Collision avoidance maneuvers according to the COLREGS. The controlled ownership (OS) is depicted in black, while the dynamic obstacle (DO) is visualized in red. Presented are, in each case, three snapshots of the scenario in sequential order. In all three cases, the OS successfully initiates a starboard-sided obstacle avoidance maneuver and subsequently follows the desired path.
• Figure 5: Anti-grounding scenario. Presented are three snapshots of the scenario in sequential order.