Model-free approach based on intelligent PD controller for vertical motion reduction in fast ferries


Abstract: A new model-free approach was investigated to control two moving aps and a T-foil of a fast ferry traveling in the head sea. Considered as a highly perturbed system, fast ferries in sea waves suffer from the undesirable effects of pitch and heave motions causing severe vertical accelerations that lead to the discomfort of passengers who then experience seasickness. To appropriately control this multivariable system, a model-free control strategy was adopted. An augmented PD controller with compensating terms resulting from an online identification of an ultralocal model of the system was designed. Relying only on input{output data and using online numerical differentiation based on a fast estimation technique, a nonphysical model was designed and continuously updated to capture all the unknown system dynamics, uncertainties, and perturbations. The resulting controller, known as an intelligent PD (iPD) controller, has been proven to be of a reduced design complexity but able to cope with the system's changing characteristics under high perturbations. The robustness to parameter variations was analyzed and compared to a classic PD controller's performance. The results showed that good reductions in the system's vertical motions and seasickness were obtained with a low computational cost. Moreover, the iPD successfully exhibited very robust behavior based on its model-free property when changing the system parameters and the operating velocity.

Keywords: Model-free control, intelligent PD, T-foil, ap, ship control

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