Abstract
This paper develops a finite-time output feedback control scheme for dynamic positioning (DP) system of ships in the presence of unmeasured states of ships, unknown dynamic model parameters and unknown time-varying environment disturbances. A novel finite-time extended state observer (FTESO) is first proposed to simultaneously and precisely estimate the unmeasured states of ships, unknown dynamic model parameters, and unknown time-varying environment disturbances in finite time. Second, based on the outputs of FTESO, the terminal sliding mode (TSM) controller is designed to guarantee that the DP system can track the position and heading at desired values in finite time with precise performance. Then, it is proved that all error signals of the closed-loop DP control system can converge to zero in finite time by utilizing the homogeneous method and the Lyapunov stability theory. Finally, the numerical simulations on a supply ship are carried out to illustrate the effectiveness of the proposed finite-time output feedback control scheme.
Highlights
Dynamic positioning (DP) system enables the ship automatically to maintain at the desired position and heading by using the thruster systems under the ocean environment disturbances from the wind, waves and currents [1] and [2]
In comparison with the existing observer design results for the DP system, the velocity of the DP system and the total disturbances acting on the DP system can be estimated simultaneously by the finite-time extended state observer (FTESO) and it is not dependent on an accurate system model
In this paper, a finite-time output feedback control scheme was proposed for the DP system in the presence of unmeasured states of the ship, unknown dynamic model parameters and unknown time-varying environment disturbances
Summary
Dynamic positioning (DP) system enables the ship automatically to maintain at the desired position and heading by using the thruster systems under the ocean environment disturbances from the wind, waves and currents [1] and [2]. With the expansion of the development of the ocean exploration and exploitation toward the deep and open sea, the DP system plays a significant role in marine applications, such as drilling platforms, pipe-laying ships, and shuttle tankers [4]. The control design of the DP system has become a hot research topic and attracted a large number of attention in theory and in practice. Considerable attention has been paid to nonlinear control systems [5] and [6]. With the progress of nonlinear control theory, some nonlinear control laws were
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