Disturbance observer-based finite-time control scheme for dynamic positioning of ships subject to thruster faults

The increasing dependence on marine resources has encouraged the rapid development of dynamic positioning (DP) technology in ships and other marine vessels. This study proposes a novel DP scheme for ships subjected to comprehensive disturbances (unknown environmental disturbances and thruster faults). An integral nonsingular fast terminal sliding mode control (INFTSMC) scheme is initially designed without accounting for environmental disturbances. This scheme has a higher convergence rate and robustness against unknown environmental disturbances than the NFTSMC scheme. Furthermore, a new finite-time disturbance observer is developed to adapt to the changes in the comprehensive disturbances and ensure that the observed errors converge within a small region around the origin in finite time. The INFTSMC scheme is then combined with the finite-time observer to create a finite-time observer-based thruster fault-tolerant control (FTOAFTC) scheme. Detailed simulation studies and quantitative analyses are carried out on the traditional sliding mode control (SMC), NFTSMC, and FTOAFTC schemes. The FTOAFTC scheme's transient and steady-state performances, robustness against environmental disturbances, and fault-tolerance ability are found to be superior to those of the other schemes.

Automated summary

This study introduces a novel dynamic positioning scheme for ships, addressing unknown environmental disturbances and thruster faults. The proposed scheme demonstrates higher convergence rate and robustness, integrating finite-time disturbance observer and thruster fault-tolerant control for superior overall performance.