Nonlinear Feedback-Based Path Following Control for Underactuated Ships via an Improved Compound Line-of-Sight Guidance

To promise the high fidelity of path following control for the underactuated ship from the aspect of the nautical practice, this paper develops a nonlinear feedback-based control scheme with an improved compound line-of-sight (ICLOS) guidance law, which has the energy-saving and efficient performance. Based on the methodology of the nonlinear disturbance observer and method of reduced-order extended state observer (ESO), a reduced-order state nonlinear sideslip angle observer is developed for online estimation of the time-varying sideslip angel caused by external disturbances, and a sideslip angle controller is incorporated to avert the sharp acting of actuators. Meanwhile, unlike the traditional line-of-sight (LOS) guidance law, a time-varying lookahead distance is designed as a function that relates to the ship' cruising speed and the cross track error, while the advance steering distance is also variable responding to the ship's length and turning angle, both of them make the turning process smoother. In the control scheme, the second-order closed-loop gain shaping algorithm (CGSA) is employed to design a concise robust controller, where the fuzzy logic system (FLS) is introduced to adjust the integral coefficient online to improve the transient performance. In addition, to further reduce the steering frequency and energy consumption of the system, nonlinear feedback technology (NFT) is adopted. Numerical simulation and comprehensive comparisons are conducted to demonstrate the remarkable performance and superiority of the proposed path following control system.