Design of reduced-order observer-based emulation controllers for dynamically positioned ships

Nonlinear sampled-data stabilization of dynamically positioned ships is considered by reduced-order observer-based emulation controllers. Using a backstepping technique, continuous-time state feedback stabilizing feedback laws for ships are designed and then under natural detectability assumption for ships linear time-invariant continuous-time reduced-order observers are obtained. Then combining an emulation of the designed state feedback laws and the exact discretization of the obtained observers, the output feedback semiglobal practical asymptotic stabilizing controllers are given for sampled-data dynamically positioned ships. A numerical example is given to illustrate the proposed design method.