Comparing Controllers for Dynamic Positioning of Ships in Extreme Seas

Abstract

This paper considers the design, implementation and experimental verification of two controllers for ship station keeping in extreme seas. In particular, the performance of two dynamic positioning controllers are compared, namely a sliding mode controller and a PID controller with acceleration feedback. The former has been tested in extreme seas before because the acceleration feedback term virtually increases the inertia of the ship, making it less sensitive to large wave loads. Sliding mode control is chosen because of its robustness to parameter uncertainties such as frequency dependency of added mass and damping. Model-scale experiments are performed in the Marine Cybernetics Laboratory at the Norwegian University of Science and Technology. The performance is measured by new performance metrics combining the energy consumption from thrusters onboard the ship with position and heading precision.