Fin-Rudder Joint Control Based on Improved Linear-Quadratic-Regulator Algorithm

Navigation accidents and disasters frequently occur when ships sail at sea owing to extreme weather, wind, and wave conditions. The disturbance of wind and waves affects the stability of the ship’s course and makes the ship roll violently. Ships are usually equipped with an autopilot to control the course and a fin stabilizer to reduce rolling during navigation and improve stability and safety. Fin-rudder joint control system considers the coupling effect of the ship’s horizontal plane motion, thereby improving the performance of the rudder and the fin stabilizer. This paper presents an improved linear-quadratic-regulator control algorithm. A rate control law with no static error is proposed based on the traditional linear-quadratic-regulator to eliminate the static error of the state vector and achieve a better control effect. Additionally, a closed-loop state observer is used to estimate the system’s state vector, and a dynamic corrector is designed to reduce rolling and heading angle deviation caused by sea wave interference. The simulation results show that the designed fin-rudder joint controller with the improved linear-quadratic-regulator algorithm can achieve more than 80% roll reduction effect at level 3 and 5 sea states, and has better course keeping ability compared with the rudder control.