Practical observer-based path following control of the guide ship with propeller and rudder in the underway replenishment

A path following control strategy is proposed for the guide ship in the underway replenishment without velocity measurements. Firstly, the detailed models of the ship and external disturbances are established. Secondly, an extended state observer is designed to estimate the linear speeds and yaw rate of the ship based on the information of position, heading, propeller speed and rudder angle. With the estimated linear speeds, the sideslip angle led by the disturbances is obtained and thus can be compensated by the update law of the desired heading. Also, an augmented state in this observer is constructed to approximate the system uncertainties and disturbances. Thirdly, two command filter backstepping controllers companied with the observer are proposed to directly control the propeller and rudder, respectively. For the proposed control system, its stability is proved by using the Lyapunov theory. Finally, the effectiveness of the proposed method is demonstrated by a simulation example.