Ship Dynamic Positioning Output Feedback Control with Position Constraint Considering Thruster System Dynamics

Abstract

In order to simultaneously address the issues of ship operating area limitation, unknown time-varying disturbances, immeasurable ship speed, unknown dynamics, and input saturation, this paper investigates the position-constrained ship dynamic positioning output feedback control, taking thruster system dynamics into account. Firstly, a barrier Lyapunov function (BLF) is utilized to limit the ship position inside the dynamic positioning system’s acceptable working range and to limit the ship position error. Second, the set total disturbance, which is made up of unknown time-varying disturbances and unknown dynamics and is further handled by the control strategy, is estimated using a fixed-time extended state observer (FDESO). Additionally, the thruster system dynamics equations are incorporated into the controller design process so that the generated thrust signal varies gradually without abrupt fluctuations, in keeping with engineering realities. Furthermore, the thruster input saturation issue is dealt with using a finite-time auxiliary dynamic system. Finally, a robust control term is introduced to handle the errors generated in the controller design. The stability proof section demonstrates that the designed control strategy can cause the ship to arrive and maintain at the desired location and heading, as well as stay continuously inside the designated operating area with all signals of the closed-loop control system being consistently and eventually bounded. The simulation results demonstrate that the proposed system is valid.

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Dynamic Positioning Control of Large Ships in Rough Sea Based on an Improved Closed-Loop Gain Shaping Algorithm

“…Guan [11] designed a controller using the sliding mode variable structure control method, and a stability analysis based on the Lyapunov function exhibited good control performance. Mu [12] considered unknown time-varying disturbances and restricted operating areas, using a fixed-time extended state observer (FDESO) to observe the total perturbation and incorporating the thruster system's dynamics equations into the controller. The above control methods are robust for nonlinear systems with uncertain perturbations, but, at the same time, they introduce a tremor-a problem that can increase mechanical losses in a propulsion system.…”