Thrust allocation is one of the key technologies of the dynamic positioning system. Its main task is to allocate appropriate thrust to each thruster according to the control force and torque generated by the controller.In the process of ship dynamic positioning, when the ocean environment force is small and the direction changes frequently, in order to resist the environmental force, the control system requires thrusters to generate a small thrust, even zero thrust. The conventional thrust allocation method cannot solve the problems that the thruster cannot generate zero thrust and the angle of the thruster changes frequently due to the environmental force. Therefore, this paper introduces the idea of group bias and designs an adaptive group bias thrust allocation algorithm based on energy optimization. The algorithm adopts an energy optimization algorithm to solve the optimization problem of thrust allocation, and is able to adjust the biasing adaptively to generate zero thrust and reduce the energy consumption of the thruster. Simulation and model test results show that the algorithm is suitable for the above conditions, which can solve the problem that the propeller is inconvenient to issue small thrust or even zero thrust in the actual engineering application, realize the fixed-point positioning control effect, and effectively reduce energy consumption and thruster wear.
The dynamic positioning system uses the thrust generated by the thruster to resist external environmental forces, thereby keeping the vessel or platform in a predetermined position or trajectory. Among them, the thrust allocation module is an important part of the dynamic positioning system. Its main function is to find a combination of optimal thrust and angle to meet the combined force and torque required by the controller.
When the dynamic positioning ship is near the positioning point or when performing fixed-point control, there are special working conditions with small control force but frequent changes in direction. The conventional thrust allocation method cannot solve the problem that the propulsion system generates very small thrust or zero thrust (Johansan, 2004; Ruth, 2007; Le, 2014). Meet the special high power requirements of the propulsion system and the inability to avoid frequent rotation or response lag of the thruster. This leads to the application of the group bias thrust allocation method in the dynamic positioning system.