Integrated path following and collision avoidance control for an underactuated ship based on MFAPC

Considering the challenges in integrated path following and collision avoidance control of underactuated ships, a model-free control method coupled with guidance approach is investigated in the present study. The collision risk assessment is performed first to determine whether collision avoidance should be considered during path following. To overcome the underactuated issue, path-following and collision avoidance tasks are transformed into a heading control problem in the guidance system by integrating line-of-sight (LOS) and modified velocity obstacle (VO) algorithms. The modified VO algorithm is characterized by adjusting the VO area, from which the smoothness of ship trajectory during collision avoidance can be enhanced. Additionally, COLREGs are integrated into the modified VO algorithm to ensure effective collision avoidance with encountering ships. To achieve accurate heading control without prior knowledge of the ship maneuvering motion model, a heading controller with the model-free adaptive predictive control (MFAPC) is developed. The heading angle and the yaw rate are synthesized as the defined output to enhance the correspondence between input and output in MFAPC. The effectiveness of the developed controller is verified by computer simulations, where the own ship stably and precisely avoids either static obstacles or encountering ships while following the desired path.