Research On Thrust Allocation Algorithms And Strategies Of Dynamic Positioning System Based On QP Algorithm

At present,the dynamic positioning system is widely used,and it has become an indispensable system for the development and utilization of deep-sea resources.The dynamic positioning system can make use of the thrust produced by the propellers to counteract the external environment force to keep the ship or platform in a predetermined position and trajectory.Thrust allocation module is an important part of the dynamic positioning system,its main role is to find an optimal combination of thrust and angle in a limited period of time to meet the requirements of the control force and torque,its performance directly affects the positioning accuracy,stability and control ability of platforms or ships.Therefore,the study on the thrust optimal allocation is of important theoretical and practical significance.The main contents of this paper include:Firstly,the mathematical model of thrust optimal allocation problem is established,which is a nonlinear optimization problem with constraints.The quadratic programming algorithm(QP)and the sequential quadratic programming(SQP)algorithm are used to solve the thrust allocation problem,and the real time and accuracy of the two algorithms are compared by simulation.Secondly,taking into account of the hydrodynamic interaction between the propellers,it will reduce the efficiency of the propeller,increase the energy consumption of the propulsion system,and affect the positioning accuracy.In order to solve the problems of existing water dynamic interference method,an improved method was put forward,which allows the azimuth thruster through the forbidden area,but limit of the maximum thrust,and avoid the propeller in the forbidden zones for a long time.In addition,for the dynamic positioning ships work in complex sea conditions,the propeller may malfunction and reduce the positioning accuracy.In order to solve this problem,a fault tolerance allocation method is proposed based on the quadratic programming algorithm,which can effectively improve the fault tolerant capability of dynamic positioning system.Finally,according to the thrust optimal allocation problem in some special sea conditions or working conditions,an adaptive group biasing algorithm is proposed.The method can adaptively adjust the size of the biasing and the combination of the full rotary propellers according to the size and direction of the control force.In addition,in order to avoid the frequent switching of the combination mode,a hysteresis switching method is proposed to guarantee the stability of the dynamic positioning system.