Robust path tracking of autonomous underwater vehicles using sliding modes

Abstract

Accurate track keeping of autonomous underwater vehicles is necessary for the autonomous navigation of a vehicle through confined spaces, and in the presence of obstacles and cross-current environments. Uncertainties in the force coefficients and environmental disturbances, as well as the required accuracy lead to the need for a robust sliding mode control for successful vehicle operations. This thesis investigates the use of a cross track error guidance law with a sliding mode compensator and presents results based on computer simulations using a nonlinear dynamic model of the Swimmer Delivery Vehicle. Steady state errors and stability requirements are evaluated analytically for a given current speed and direction, and are confirmed through numerical integrations. The use of integral control and disturbance estimation and compensation methods are developed in order to achieve the desired steady state accuracy. A leading track control monitoring technique is used to eliminate track overshoot during turning and reduce the rudder activity. Finally, the effects of measurement noise are evaluated and guidelines are developed for suppressing them.