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

This paper presents an indirect adaptive type-2 fuzzy logic controller (FLC) as well as a direct adaptive type-2 FLC for tracking control of surface vessels under time-varying hydrodynamic disturbances. The combination of approximation-based adaptive control technique and type-2 fuzzy logic system (FLS) allows us to handle time-varying disturbances without exact information on them. The stability of the design is proved through Lyapunov analysis where globally asymptotical convergence of the tracking errors is guaranteed. Although designed from different points of view, both indirect and direct adaptive type-2 FLC yield same and passive closed-loop systems. Comparative simulations with their adaptive type-1 counterparts are carried out. The proposed techniques are found to be effective, robust, and reduce tracking errors.