Design of a State and Disturbance Reduced-order Observer for Sampled-data Underactuated Ships with Constant Disturbance

The design of reduced-order observers that estimate both unmeasured velocity and disturbance of sampled-data ships with unknown constant disturbance is considered. When the angular velocity of yaw of ships is small, it is shown that the reduced-order observer is semiglobal and practical in T fot the exact model of sampled-data ships. The proposed design of reduced-order observers is applied to the circular path following control of sampled-data underactuated ships with unknown constant disturbance where the angular velocity of yaw becomes small. The efficiency of the proposed design is shown by simulation results.