Improved ELOS based path following control for underactuated surface vessels with roll constraint

This study aims to the path following control of underactuated surface vessels with an improved extended state observer based line-of-sight (ELOS). The large roll motion and nonzero drift angle can affect the guidance law and the course tracking accuracy in rough waves, the two factors should be considered when the path following control system is designed. The robustness of the tracking control system is enhanced by handling the system dynamic uncertainty and external random disturbances. First, the roll motion based track error dynamics are established, then a reduced order extended state observer is applied to estimate the time varying drift angle, and the adaptive heading guidance law is proposed. Finally, a robust adaptive heading control law is developed by combining dynamic surface control, sliding mode control and backstepping techniques. The ELOS based path following control methodology can ensure that all estimation and track errors are uniformly ultimately bounded. Simulations were used to illustrate the effectiveness of the proposed controller by comparing it with sliding mode control.