Study On Fault Tolerant Control Via Sliding Mode Technology For Dynamic Positioning System Of Ships

With the deepening of marine development,the traditional anchoring positioning technology has been difficult to meet the positioning requirements of the deep sea operations.The dynamic positioning system has been widely used in complex positioning operation in the deep sea,such as drilling,cable-laying,pipe-laying,supply ships and offshore platforms because of its unique maneuverability,high precision and unlimited water depth.It has become an indispensable key technology for the resource development in the deep sea.However,the thrusters of the ship have been operating in a harsh marine environment for a long time in actual operation,the faults may occur.But the nature of the dynamic positioning ships makes it difficult for the faulty thruster to be repaired or replaced with a spare one in time.In order to improve the reliability of the system and ensure the safety of the operation,it is necessary to design a fault-tolerant control scheme for the dynamic positioning ships to complete assigned tasks when the thruster malfunctions.Therefore,it is of great theoretical significance and practical engineering value to study the fault-tolerant control problem of the dynamic positioning with actuator fault.The main research work of this paper is as follows:Firstly,the fault-tolerant control problem of the dynamic positioning ships subjected to unknown external environmental disturbances is studied.A fault-tolerant control scheme based on sliding-mode state feedback is proposed,which covers three thruster fault situations such as loss-of-effectiveness,stuck,and outage.The lower bound of the fault information and unknown upper bound of the disturbance are estimated online through the adaptive mechanism.Then an adaptive sliding mode control law is designed without relying on the fault detection module and the upper and lower bounds of the fault information.With the help of Lyapunov stability theory and sliding mode control theory,the designed adaptive sliding mode controller can ensure the uniform boundedness with all signals when the dynamic positioning system of the ship is subjected to thruster fault and external boundary disturbance in the marine environment.The simulation results have showed that the effectiveness of the proposed control algorithm.Secondly,the robust fault-tolerant control problem of the dynamic positioning ships subjected to unmeasurable velocity information of the ship external is studied.A high-gain observer is designed to estimate the unknown speed information,and the fault information and unknown external information are estimated ouline through the adaptive mechanism.Then,an adaptive sliding mode control law is designed using the above information,with the help of sliding mode control theory,it is proved that the designed adaptive sliding mode controller can ensure the position error of the ship's dynamic positioning system reaches the sliding mode area within a finite time when the dynamic positioning system of the ship is subjected to unmeasurable velocity information,thruster faults and extermal boundary disturbance in the marine environment.The simulation results have showed that the effectiveness of the proposed control algorithm.Finally,the fault-tolerant control problem of the dynamic positioning ships subjected to unknown model parameters of the ship is studied.The radial basis function neural network adaptive method is introduced to approximate the unknown ship model.The sliding mode control law is designed using the above estimated information,with the help of sliding mode control theory,it is proved that the designed adaptive sliding mode controller can ensure the position errors of the ship's dynamic positioning system reach the sliding mode area within a finite time and the simulation results have showed that the effectiveness of the proposed control algorithm.