Event-triggered robust fuzzy path following control for underactuated ships with input saturation

To promise the high fidelity of path following control for the underactuated ship, this paper develops an event-triggered robust fuzzy control scheme, which also releases the constraint of input saturation. To solve the underactuated problem, we add an adaptive bounded term to the tracking error in the sway motion, which allocates the error to actuated motions. In the control scheme, the fuzzy logic systems (FLS) are employed to approximate the uncertainties, while the methodology of robust damping is adopted. The Gauss error functions are introduced to approximate the structure of input saturation, such that the backstepping frame can be applied, and the control commands in the rudder angle and the revolving rate of the main engine are derived. To avert the frequent acting of actuators, the event-triggered control (ETC) technique is adopted. The static triggered condition is constructed with a flexible adjustable variable, which regulates the minimal inter-event times for actuators. Via the direct Lyapunov approach, we prove the existence of the minimal inter-event time and the uniform boundedness of all tracking errors in the closed-loop system. Finally, the feasibility of the scheme is validated in the platform of the simulated ocean environment.