L1 adaptive control used in path following of surface ships

In this paper, a cascaded control structure and the L₁ adaptive control law are used to deal with the path following problem of surface ships. The guidance-based strategy separates the geometric task from the ship motion control system. The whole control problem is decoupled into two subsystems, namely the outer-loop guidance subsystem and the inner-loop control subsystem. The outer-loop subsystem only concentrates on the geometrical part of the system and generates a desired yaw rate which guarantees the convergence of the ship to any proper given path. The desired yaw rate is then regarded as the reference output of the inner-loop control subsystem. Considering about the model uncertainty, the L₁ adaptive control strategy is used to deal with the inner-loop control subsystem. The L₁ adaptive method has a fast adaptation rate and robust control performance, which can ensure the uniformly bounded transient and asymptotic tracking performances. Besides, the L₁ theory is relative simple and easy for industrial implementation. The results show the effectiveness of the control law to the path following problem of ships.