Research On The Redundant Controller Of Dynamic Positioning System

In spite of variously complex marine environment,Dynamic Positioning System makes ships a fixed station or direction by adjusting power equipment automatically.With the development of ocean engineering,it has become a necessary supporting system for ships operating at sea,and it is used in field of the laying of submarine pipelines,fixed point operation and sea rescue.As the reliability of Dynamic Positioning System is related to the safety of ship and personnel,the requirement of its reliability had attracted more attention.Then the redundancy technology began to be used in Dynamic Positioning System.It helps reduce the effects of faults and maintain the normal operation by equipment redundancy,which improves the fault tolerance ability of Dynamic Positioning System.The research object of this paper is redundant controller of Dynamic Positioning System.The redundancy of controller makes the output of controller not affected by some faults.It achieves the fallowing functions: synchronous operation of three control computers;providing right control command and shielding the error data of sensor and controller by input and output vote of controller;detecting failures and identifying it is a transient fault or permanent fault;completing system reconstruction when it is permanent fault.The main contents are as follows:First of all,from the point of the redundant system reliability,combining with the requirements of Dynamic Positioning System,a structure of the Triple Modular Redundancy based on network communication is designed.It shields the error data of sensor and controller by input and output vote of controller.Combined with fault detection mechanism,this structure can make the Dynamic Positioning redundant controller working in triple,double modular redundancy mode,single machine work mode and security mode.Secondly,triple synchronization strategy is adopted according to the characteristics of the Dynamic Positioning System cycle task.The CNA synchronization is used for cycle synchronization.Its disadvantage is fault machine can't automatic join redundant system after recovery.Therefor a layer of network synchronization is added by the method of master-slave synchronization.Then task synchronization is used in a cycle.Three layers of synchronization ensure synchronization execution of task.Secondly,the prediction optimized improved-history-based weighted average voting algorithm is proposed.Consistency value and smoothing degree have been added to improve history based voting algorithm.Besides,grey theory is used to improve the safety of the novelalgorithm in the state of multiple faults.Thirdly,in order to improve the fault tolerance function of system,voting detection and heartbeat inspection technology are used to monitor system fault state,which provides the basis for system reconstruction.Finally,experiment was carried out on the redundant controller designed in this paper in QNX.Final conclusions are made by analysis of the performance of the system in different fault conditions.The test results show that the system can keep synchronization,provide stable and correct voting output and automatically adjust its structure.The design in the paper is able to meet the expected design requirements.