Handling Unknown External Forces with Highly Responsive DP Controller
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Rising marine activity in the arctic has introduced many ice related challenges forDynamically Positioned (DP) marine vessels. Current motion control systems forDP vessels are not designed to handle ice-related disturbances, and will thus needto be improved to be able to operate in these challenging conditions. The main goals of this master thesis have been to evaluate opportunities for handlinglarge and sudden unknown external disturbances, and compare these withexisting solutions. There will be presented a predictive feedforward controller to minimize the impactof an external disturbance. There will also be presented a selective wave filterwith a notch frequency that is adapted by a wave-frequency tracker.A modified highly responsive PID controller with nonlinear stiffness and dampingterms has been derived, and proven globally asymptotically stable using Lyapunovbased stability analysis. There will also be presented a Disturbance Rejection byAcceleration Feedforward controller that utilizes acceleration feedback from inertialmeasurements. All of the proposed improvements have been implemented and tested in Matlab/Simulink, while some of the methods have been implemented and tested hardware-in-the-loop in a simulator provided by Marine Technologies. The proposed methodswere shown both theoretically and through simulations to yield improved stationkeepingperformances.