Terminal sliding mode for robust tracking control of underactuated surface vessels

In order to realize tracking control for underactuated surface vessels with parameter uncertainties and external disturbances, a nonsingular terminal sliding mode method was proposed. The controller was divided by backstepping method into the kinetic part and the dynamic part. In the kinetic process, the reference surge and sway velocities are employed as the virtual control law in stabilizing the position errors. In the dynamic process, the virtual control law was considered the new tracking target, and the real control law was designed by the nonsingular terminal sliding-mode method to realize the tracking control of the reference velocities. This method can not only guarantee the position tracking error converge finite time, but also ensure yawing motion is BIBO stable. Eventually, simulation experiment of real ship is performed. Results validate the proposed controller can achieve fast tracking control of USV in finite time under parameter uncertainties and external disturbances.