Path tracking control of underactuated surface vessels based on the differential flatness

For the path tracking direct control of underactuated surface vessels, because there are underactuated and nonlinear properties in the control system, the method of static feedback linearization can not be applied into the control law designing procedure. Here, the path tracking control system of underactuated surface vessels in horizontal plane was first proved to be a differential flatness system. Based on the feature that all state variables are the function of flat output and its derivative in differentially flat systems, the method of direct dynamic feedback linearization was adopted for the path tracking control of underactuated surface vessels. The equivalence equations were derived and decoupled into two linear controllable systems. Then the control law was derived such that the tracking error with respect to the planned path could be stabilized asymptotically and globally, even under disturbance. The method relaxes the assumption of persistent exciting in yaw rate required in other methods. At last, the effectiveness of the proposed method is illustrated by simulation tests.