Auto Tuning of PID Controllers for Dynamic Positioning Systems with Nonlinearity

Abstract

This paper describes an application of Fictitious Reference Iterative Tuning (abbr. FRIT) to the Dynamic Positioning System (abbr. DPS), which is an automatic control system for ship positioning. We developed the motion equation including nonlinear fluid forces with respect to the relative velocity between a vessel and a current and adjusted control parameters by employing FRIT to such a nonlinear system. We mentioned that it was difficult to design the desired transfer function appropriately and proposed to use known information about a real plant. In particular, we used a nominal plant model to design desired transfer function. Furthermore, since disturbance attenuation is the primary purpose in the DPS, we designed the evaluation function which provides the control parameters that give the desired output response to the input disturbance (e.g. wind, wave). The simulation results show that the evaluation function based on the load disturbance sensitivity function (quasi sensitivity function) gives a better output response to the disturbance than the sensitivity function.