Path Control of Surface Ships Using Sliding Modes

Abstract

The surface ship path control problem is formulated as a nonlinear state space control problem subject to disturbances, modeling errors, and parameter uncertainty. A "destroyer study" ship using a nonlinear maneuvering model is used as the system model. The system to be controlled is highly nonlinear with parameters that vary with speed and operational conditions. Uncertainty in the force coefficients, as well as in disturbances of the seaway lead to the need for a robust control for navigational accuracy. This paper investigates the use of cross track error and line-of-sight guidance laws with a sliding mode autopilot for path control of surface ships, and presents results based on computer simulations using the model described above. The results illustrate the simplicity and effectiveness of the robust control design for compensating the nonlinearities and disturbance effects with improvements in the navigational accuracy. Comparisons between the two guidance schemes are presented and guidelines are developed with respect to proper guidance selection.