Design of terminal sliding mode based controller with Prescribed performance function for ship dynamic positioning system

In this paper, a controller is designed to automatically control and keep the ship positioning, in a way that, it has ability to keep the ship at a coordination, automatically transfer the ship from one coordination to another one, and it’s also able to track a target without model uncertainties. To increase the accuracy and speed of the controller response, a backstep controller based on the terminal sliding mode is used, which guarantees the time-limited stability of the tracking error without depending on the initial conditions of the system. Also, in order to guarantee the controller's transient performance, a prescribed performance function is used in the controller design method. The designed controller, while guaranteeing the performance of the tracking error within a prescribed range, stabilizes the ship response in a constant time without dependence on the initial conditions of the system in a limited time so that the tracking error converges to a neighborhood of the target point. In order to validate the designed controller, the desired controller is tested in MATLAB environment on a ship model and the results show that the designed dynamic positioning controller is able to control the ship positioning well and all the theoretical findings are confirmed.