Tracking control of surface vessels via adaptive backstepping interval type-2 fuzzy logic control

This paper investigates the problem of tracking control of fully actuated surface vessels along a desired trajectory in the presence of time-varying hydrodynamic disturbances. The combination of approximation-based adaptive technique and interval type-2 fuzzy logic system allows the time-varying disturbances to be handled without explicit knowledge about the disturbance model. Through backstepping and Lyapunov synthesis, an indirect adaptive interval type-2 fuzzy logic controller (IT2 FLC) as well as a direct adaptive IT2 FLC for the tracking control problem are introduced. The stabilities of the closed-loop systems are explored where sufficient conditions for guaranteeing global asymptotical convergence of the tracking errors are proposed. Comparative simulations of the proposed techniques against their adaptive type-1 counterparts are carried out with a container ship. The proposed techniques are found to be effective and robust.