Tracking control of an underactuated surface vessel

We consider tracking control of a surface vessel with only two control inputs. The surface vessel model has certain similarities with chained form systems, but cannot be transformed to chained form. In particular, the model has a drift vector field as opposed to the drift-free chained form systems. It is shown, however, that methods developed for tracking control of chained form systems, can be used for developing a tracking control law for the surface vessel. Through a coordinate transformation the model is put in a triangular-like form which makes it possible to use integrator backstepping to develop a tracking control law. The control law steers both the position variables and the course angle of the surface vessel, providing semi-global exponential stabilization of the desired trajectory.