Research On Hybrid Controller For Dynamic Positioning Based On Sea Condition Changes

With the march of mankind to the deep ocean, dynamic positioning systems are becoming increasingly widely used in ships(research vessels,semi-submersible vessels,etc),offshore platforms (ocean drilling platform, etc.),underwater vehicles (ROV)and military ships(mine ships, submarine mother ships, etc.). Dynamic positioning systems usually contains three parts:position measuring system, control system and thrust system. Position measurement system (sensor) is used to measure the current ship's position,the controller with the expectations based on tracking ship position deviation, calculated to resist environmental interference power (wind, wave and current),the position of the ship back to the expectations of the required thrust, and energy management system allocate the thrust of each thrusters need,the thrust generated by the ship (platform) interference in the storm flow to maintain the set course and the ship's position. Dynamic positioning system is the control technology, it marks the level of the development of dynamic positioning system.Dynamic positioning system should be able to operate in varying operational conditions from calm to extreme seas, meet the need of different task, have dependability and be economical. Meanwhile, dynamic positioning system should increase the so-called weather window, the operational availability should be improved and possible to conduct long time marine operations also. To solve the problem that dynamic process change acutely, hybrid controller have better performance than single controller.This paper derived mathematical model of dynamic positioning vessel under reasonable assumption, by analyzing of kinematics and dynamics of the vessels. Then, the characteristics of propellers and rudders were researched and modeling. The estimate model of the second order wave force was researched.Based on supervisory and switch thoeries of linear and nonlinear systems, the dwell-time switching logic and scale-independent hysteresis switching logic were researched. The new concept of dynamic positioning was introduced, that was combining controllers of different targets to a hybrid-controller for solving limitations of single controller and improving the safety in changing environment. Finally, dynamic positioning hybrid-controller and a observer were designed, and the stability of them were proved. Numerical simulations were conducted to verify that the designed hybrid-controller was effectual and feasible.