Adaptive robust nonlinear design of course keeping ship steering autopilot

This paper develops an adaptive robust control design strategy for automatic steering of ships with unknown parameters under unknown environmental disturbances induced by wave, wind, and ocean current. Based on the incorporation of the Nussbaum-type function into backstepping design and some technical lemmas, the proposed design method does not require a priori knowledge of the sign of the unknown coefficient. It is proved that the designed adaptive robust controller can guarantee the uniform ultimate boundedness of the resulting closed-loop system signals. The control performance can be guaranteed by an appropriate choice of the design parameters. Simulation results on a 45 meters long ship are presented to validate the proposed controller.