Research On Model Predictive Control Of Ship Dynamic Positioning System

With the strategy of "Sea Power" in China, our country will invest a lot of manpower, financial and material resources to enhance the efforts of exploration of offshore oil and gas resources. It is not only the important demand of China’s international status and energy strategy, but also the need to defend the blue territory. Dynamic positioning system has become one of the key equipments and core technologies in the ocean engineering. For offshore vessels, its operating environment is relatively complex, and the demand for positioning is much stricter. Therefore, the technology of dynamic positioning has been widely used. As the key core of the dynamic positioning system, the control system performance is directly related to the operating conditions and accuracy of positioning. Therefore, it is very important to carry out the research on the dynamic positioning control system.In this paper, a positioning control system research for an offshore supply vessel, theory and simulation experiments methods were used, and research on the dynamic positioning control system.Firstly, two kinds of coordinate systems were established:earth-fixed-reference coordinates and the body-frame coordinates. According to motion and dynamics characters of the dynamic positioning vessel, a mathematical model of the dynamic positioning of the low-frequency motion state space model was established. Research on the wind, waves and currents, the simulation modules of the disturbance force and torque of the wind,waves and currents were established based on Matlab/Simulink to simulate real ocean environment load. Research on the model predictive control algorithm based on the state-space equation, a controller was designed which can be applied to the dynamic positioning vessel and the simulation module of the MPC controller was established by Matlab/Simulink. In order to improve the performance of the controller, the constraint handling methods and the design of the state estimator were introduced. Based on the modularization theory, the above simulation modules were established, and the DP-SSMPC simulation platform was set up. Finally, the positioning and directional capabilities of the offshore supply vessel was done, which in the condition of calm water, and different combinations of environmental conditions for wind, waves and currents. The simulation results show that the model predictive controller can make the dynamic positioning ship reach the set position accurately under the disturbance of the external environment, and the control process can meet the requirements of fast, stable and accurate, and the effectiveness of the proposed controller was demonstrated.