Concise robust fuzzy nonlinear feedback track keeping control for ships using multi-technique improved LOS guidance

In order to solve the problem that the parameterized LOS (line-of-sight) guidance cannot be directly applied to the navigation practice, this paper proposed an indirect nonlinear feedback concise robust track-keeping control strategy for ships, which consists of a robust course-keeping controller and a MILOS (multi-technique improved LOS) guidance system. The second-order closed-loop gain shaping algorithm was employed to design the linear course-keeping controller, then the fuzzy logic system was used to adjust the integral coefficient online to improve the transient performance. The introduction of nonlinear feedback technique further reduces the steering frequency and saves energy. For the guidance system, three techniques are introduced to enhance the track-keeping effect. A nonlinear sideslip angle observer is developed to eliminate the static track error caused by the wind and current interference. A time-varying lookahead distance and a new advance turning distance are proposed to achieve the smooth turning between track sections. Simulation results show that compared with the conventional LOS guidance, the proposed strategy is more consistent with the requirement of navigation practice and has comprehensive advantages in both dynamic and static performance, which is of great significance for enhancing the ability of ship's autonomous navigation. The novelty and contribution of this paper can be briefly concluded as following points:•The second order closed-loop gain shaping algorithm is employed to design a PID controller in series with a first order filter for course-keeping.•The fuzzy logic system is used to adjust the integrate coefficient online to improve the dynamic performance of the course-keeping system.•A nonlinear sideslip angle observer is constructed based on the conventional LOS guidance frame.•A new advance turning distance setting strategy is proposed.