Path following of underactuated surface ships with uncertain forward speed

The control problem of path following with an uncertain forward speed is concerned for an underactuated surface ship with second order nonholonomic constraints. An increment feedback controller is developed based on nested nonlinear sliding modes which are decentralized and iteratively designed in the augmented states space. Without a known reference course to be generated by an accurate model, the underactuated path following control objective can be achieved by single input of rudder angle. The saturation on actuator and unknown environmental disturbances are also explicitly considered. And the yaw velocity PE (persistent excitation) condition is not required, so the controller can also be used for way points tracking. Computer simulation results on a full nonlinear hydrodynamic model of M.V YULONG are provided to validate the effectiveness and robustness of the proposed controller.