Hybrid observer for improved transient performance of a marine vessel in dynamic positioning*

Dynamic positioning (DP) systems are used on marine vessels for automatic station keeping and tracking operations solely by use of thrusters. Observers are key components of DP systems, and two main types are proposed in this paper. The model-based type is used in steady state conditions since it is especially good at filtering out first order wave induced motions and predicting states in the case of signal loss, and the signal-based type typically has superior performance during transients. In this paper a hybrid observer including a signal-based part and a model-based part with a performance monitoring function is proposed. The observer part that provides the best estimate of the vessel position and heading is used in closed-loop control, thereby allowing for improved transient response while maintaining good steady-state performance. The contributions of this paper include the design of a hybrid signal-based and model-based observer with performance monitoring, stability analysis of the vessel with hybrid estimates in output feedback control, and simulations of a platform supply vessel during a set point and heading change.