The next generation marine control systems will, as a step towards increased autonomy, have more automatic functionality in order to cope with a set of complex operations in unknown, challenging and varying environments while maintaining safety and keeping operational costs low. In this paper a hybrid control strategy for stationkeeping and maneuvering of marine vessels is proposed. The hybrid concept allows a structured way to develop a control system with a bank of controllers and observers improving dynamic positioning (DP) performance in stationary dynamics, changing dynamics including enhancing transient performance, and giving robustness to measurement errors. DP systems are used on marine vessels for automatic stationkeeping and tracking operations solely by use of the thrusters. In this paper a novel method improving the transient response of a vessel in DP is developed. The performance of the hybrid control system, including two observer candidates and one controller candidate, is demonstrated in model-scale experiments and on full-scale field data. The hybrid system has global stability properties.

In order to validate relevant dynamic positioning (DP) control algorithms in a realistic environment, a full-scale DP test campaign, the AMOS DP Research Cruise 2016 (ADPRC’16), was organized in a collaboration between the NTNU Centre for Autonomous Marine Operations and Systems (NTNU AMOS) and the company Kongsberg Maritime onboard the research vessel (R/V) Gunnerus. To the authors’ best knowledge, closed-loop DP feedback control algorithms have never been tested full-scale on a ship in an academic research experiment before. However, we have now achieved this by coding our algorithms into a test-module of the DP system, as prepared by Kongsberg Maritime. Among the tested algorithms is an output feedback control law with both good transient and steady-state performance. In another experiment, different adaptive backstepping control laws for DP were tested to compare and contrast their performance and properties. A hybrid state observer with a performance monitoring function proposed to switch between two observers, choosing the best one at any time instant, was also part of the test scope. For this, necessary measurements (including acceleration measurements) were logged to be able to rerun and validate the observer algorithms in post-processing. Finally, several experiments were done to test a pseudo-derivative feedback control law for DP. The feedback mechanism was tested with and without a feedforward disturbance rejection term, called acceleration feedforward. This paper reports the experimental setup, test program, and an overview of results from the ADPRC’16 campaign.

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This paper investigates different methods for compensating the mean and slowly varying environmental loads, and unmodeled dynamics (bias loads) in dynamic positioning of marine vessels. Four different methods are compared; using the bias estimate from an observer tuned to estimate position and velocity well, using a wave-filtered version of this bias load, using the estimate from a separate observer tuned to work well for estimating the bias loads, and finally traditional integral action on the tracking errors. The results show that the bias from the bias observer is the best solution, both in transients and steady state. Standard integral action matches the steady state performance, but is slower in transients. The estimate from the observer used for position and velocity is fast in transients, but too oscillatory in the bias state. The wave-filtered version of this has less oscillations, but falls short compared to the other methods due to added phase lag from the extra wave filter. Using a bias estimate from an observer has benefits over typical integral action, such as the possibility of offline or openloop tuning and avoiding integral windup issues. For the comparison study, a 6 DOF simulation model of a supply vessel is used.