A nonlinear sliding mode control system for a ship’s course and rudder angle

To effectively solve the problem of interference caused by the change in rudder angle during the process of controlling a ship’s course, nonlinear mathematical models of the control systems for a ship’s course and rudder angle were established. The models were based on the motions of a ship and the working principle of the steering gear. In addition, sliding mode variable structure (SMVS) theory was used to study the simultaneous control of the two state variables, i.e., the ship’s course and the rudder angle. First, for the high-order linear ordinary differential equations, suitable switching hyperplane and stable sliding mode motion equations were obtained. Then, using an affine nonlinear method, on the basis of obtaining the switching function, the SMVS controller structure of the nonlinear model was solved. Finally, a Simulink simulation was performed in the MATLAB software environment. The results show that SMVS theory has a good controlling effect on the nonlinear control system for a ship’s course and rudder angle.