Applicability of sliding mode control in autopilot design for ship motion control

The ship autopilot design is an active area of research and application of optimum controllers leads to saving of time, fuel cost, manpower and provides comforts to the crew as well as longevity to the machinery. However practical implication poses various challenges since a ship is always under unknown parametric uncertainties which are of structured as well as unstructured nature. In this paper a simple yet effective sliding mode controller is designed wherein signum function of the controller is replaced with a smooth switching function within a boundary layer in the vicinity of switching surface to reduce chattering phenomenon. Third order yaw rudder model has been used based on Nomoto´s second order yaw rate rudder model. Numerical analysis carried out and the results are presented to show the robustness of the controller. Finally its applicability onboard a naval ship is discussed.