Gain-Scheduling PID Low-Level Control for Robotic Sailboats

The sea imposes a set of restrictions that substantially influences the development of control systems for robotic sailboats. Nonlinearities produced by events such such as currents and waves are introduced that makes it more difficulty to develop effective systems to work in such environment. Towards solving the navigation problems that appear, we propose a new methodology for the control of an autonomous sailboat, which differs from others in the literature by applying a suitable PID parameters at each different maneuvering. Our methodology consists of identifying the best control (i.e. control parameters) for a given mission through simulations of the mathematical model of the sailboat. To this end, we came up with a controller, called Proportional and Integrative Gain-Scheduling control, or GS-PI, which basically consists of a table with a set of proportional and integrative parameters that best suits the control requirements of a given wind speed/direction. Results of various experiments in simulation show an improvement in the sailboat performance using the GS-PI strategy, mainly in narrow environments, when compared to classical PID approaches using a single set of control parameters during the entire navigation.