Research On Control Algorithms And Strategies Of Ship Dynamic Positioning System

With the increasing world population and the rapid development of the industry,the utilization of land resources has been depleted,and the exploitation of marine resources has become the focus of the marine development of existing marine powers.As marine environment is complex and changeable,the advanced and reliable marine equipments have become an essential part of the exploitation of deep-see resources,among which the ship dynamic positioning system(DPS)is the most brilliant jewelry.The DPS is a closed-loop feedback control system,relying on its own propulsion system to resist the external environmental loads,so that the ship can alternatively keep the desired position and heading or make auto-navigation as predefined.This thesis has mainly done some research works related to station keeping mode and path following mode of the DPS.The main research contents and results are as follows:(1)For the station keeping mode of the DPS,this thesis has respectively designed the passive-input PID controller,the passive-input LQ(Linear Quadratic)controller and the passive-input backstepping controller with the output of passive observer been the control input,and has also given the corresponding stability analysis,thus the stability of observer-control cascaded system was ensured.In addition,the actuator dynamics have been added into the DP low-frequency mathematical model,and the innovative design of the passive-input inverse optimal backstepping controller with actuator dynamics has been put forward with the present two-step inverse optimal procedure extended to three-step procedure to make the ship control has a strong anti-jamming capability,therefore optimizing the energy consumption for station keeping mode and reducing the wear and tear of the propellers.This thesis has also researched the weather optimal control(WOC)to simplify the design process of existing WOC,and a new circle-center control law was proposed as well as a passive-input PID controller was adopted,therefore accelerating the response speed of the system and improving the accuracy of position keeping.(2)For the path following mode of the DPS,this thesis has researched the planning path,guidance system and control system.For path planning,this thesis hasput forward a modified path planning method based on straight lines and circle arcs which improved the accuracy of path planning,and has also designed a continuous curvature path passing through all the waypoints which satisfied the different accuracy requirements for path planning.For guidance system,this thesis has proposed the modified time-varying line-of-sight(LOS)guidance law,the modified integral LOS(ILOS)guidance law and the two-step LOS guidance law based on the continuous-curvature path,making the path following have a quick respond and obtain a better effectiveness.For the control system,the thesis has designed the backstepping controller with actuator dynamics which satisfied the control objetives of path following.Finally,the model experimental results have clarified the influence of ship speed and circle radius on the performance of path following with straight-line and circle-arc path,and also have verified the effectiveness of the time-varying LOS guidance law and the two-step LOS guidance law with the continuous-curvature path.