Integrated Rudder/Fin Control With Disturbance Compensation Distributed Model Predictive Control

For the ship sailing in the seaway, usually the rudder is used to control the heading and the fin stabilizer is used to reduce rolling. However, there are interactions between their control effects, which usually deteriorate the control performance. The interactions can be used to enhance the control performance, if rudder and fin stabilizer are controlled to work in coordination, and this is usually called the integrated rudder/fin control. In this paper, a new control method based on distributed model predictive control (DMPC) and disturbance compensation mechanism is proposed to achieve the integrated rudder/fin control. MPC controllers are designed for rudder and fin stabilizer respectively to fulfill their different control requirements. Communication between the MPC controllers is established to make the rudder and fin stabilizer work in coordination. An extended state observer is adopted as the disturbance observer to estimate the lumped disturbance of roll motion which consists of model mismatch and external disturbance. The MPC controllers calculate control actions with the lumped disturbance to improve the control performance. They also avoid actuator saturations by limiting the control actions, which makes the control more robust in sever sea conditions. Simulation study shows that, with the proposed control method, the roll stabilization performance is enhanced and the heading control capability is preserved. The proposed control method also shows a more desirable control performance in roll stabilization compared with a well-tuned LQR controller.