Path following of under-actuated ships based on model predictive control with state observer

A model predictive control (MPC) method with linear extended state observer (LESO) is presented to address the problems of the input constraints, uncertain parameters and external disturbances for path following of under-actuated surface ships without velocity measurements. The line of sight (LOS) guidance algorithm is employed to convert the path following into the heading control flexibly. The proper reference paths at waypoints are formulated by a variable acceptable radius approach. The matters of the heading control, input constraints including rudder amplitude and rate limit are addressed by virtue of MPC method employing the Norrbin model as the internal model. The LESO is introduced to estimate the uncertain parameters and external disturbances for the improvement of the internal model accuracy and the controller robustness. Moreover, the nonlinear observer and LESO are used to approximate the surge velocity, sway velocity and yaw rate, respectively. The effectiveness of the proposed control law is demonstrated via the compared simulations.