Compound line-of-sight nonlinear path following control of underactuated marine vehicles exposed to wind, waves, and ocean currents

This paper investigates the problem of non-linear path following control of underactuated marine vehicles in the horizontal plane. Firstly, appropriate kinematic and dynamic models are established, where the kinematic model is developed in terms of the relative velocity with respect to the ocean current disturbances, and the dynamic model is developed to include the effects of wind and wave disturbances. Based on the time delay control method and the reduced-order linear extended state observer (LESOs) technique, an improved compound line-of-sight (CLOS) guidance law is first proposed which can estimate the unknown sideslip angle and can compensate for the effects of time-varying ocean currents. Secondly, the control law is decomposed into the kinematic and dynamic controllers by the back-stepping technique. The high-order tracking differentiator is applied to construct derivatives of desired yaw angle, which are calculated by the CLOS guidance law. This approach resolves the problem of computational complexity inherent in the traditional back-stepping method and simplifies the overall controller. The lumped disturbances caused by waves and wind are estimated and compensated by the reduced-order LESOs. Finally, stability analysis of the closed-loop system is performed. The simulation results and comparative analysis validate the effectiveness and robustness of the proposed control approach.