Research On Fault Tolerant Control Methods For Dynamic Positioning Vessel With Thruster Faults

With the rapid expansion and extension of national strategic interests and strategic spaces,the development of marine industry has gradually become an important part of national development.Under this background,the marine engineering equipment has been developed rapidly.Dynamic positioning vessel has been widely used in marine engineering with the advantages of high positioning precision,good flexibility and location without the limitation of ocean depth.However,as the dynamic positioning vessel always suffers abominable marine environment,and in the event of the accident during operation,for example,deep-sea drilling,it will cause serious environmental pollution and threaten the safety of the workers,so the requirement of safety and reliability for vessel operation is getting higher and higher.It is required that the dynamic positioning vessel must have a certain fault tolerant ability to deal with the acceptable faults happened in the regular task and meet certain performance index and continue to complete the operation on the premise of ensuring the safety of the operation ship.In order to achieve safety operation of dynamic positioning vessel,this dissertation focuses on thruster fault which is the main fault causing loss of position of the dynamic positioning vessel,and studies the fault tolerant control method for faulty vessel based on the analytical redundancy.The main contents in this dissertation are presented as follows:Firstly,we established the three degree of freedom motion model and propulsion system model for the dynamic positioning vessel.In view of the input saturation of the propeller during operations,a faulty matrix of thruster saturation failure based on the fuzzy set theory is proposed and established.And the open-loop model test simulation verification is carried out based on the established model.Secondly,in view of the nonlinear motion equations of the vessel,and considering the complete failure fault of partial thrusters,a new type of thruster reconfiguration block which can be applied to the nonlinear systems is proposed and placed between the original nominal controller and the faulty vessel.It is ensured that the outputs of the faulty vessel can follow the nominal one under the command signal of the reconfiguration block and the readjustment of the original nominal controller is avoided.The integral sliding mode variable structure control method is designed based on the nonlinear term in reconstructing module.Where,the adaptive control technique solves the problem of unknown boundary of the deviations of the uncertain term caused by the system nonlinearity and the disturbance of the external environment on pre/post fault.And then,the adaptive sliding fault tolerant control method with anti-saturation reconfiguration block is developed by the establishment of the faulty matrix of thruster saturation failure and the construction of the saturation function to achieve the double weakening of the thruster input saturation.The simulation results demonstrate that the method can ensure the stability of the vessel and guarantee the smooth completion of the operation task under the condition of the failure of the vessel propulsion system and the saturation of all the propellers.Then,considering that the real-time performance of system fault tolerant based on reconfiguration block to achieve active fault tolerant control is relatively weak,in order to further improve the fault tolerant capability of controller for the dynamic positioning vessel’ thruster faults,and combining the finite time fast response problem,the finite time fault tolerant control strategy with the time-varying sliding mode method is presented for the trajectory tracking control of dynamic positioning vessel.With this method,the neural network is used to approximate to the uncertain part of the system model and the adaptive technique is used to estimate the total upper bound value composed of external disturbances,thruster faults and approximate error of the neural network so that the fast tracking of the desired trajectory is achieved for vessels.The simulation results show that the method can ensure the asymptotical stability of trajectory tracking error in the case of serious failure of the ship propulsion system.The tracking control task can be finished in a limited time while guaranteeing the safety and real-time performance of the dynamic positioning ship.Finally,in view of the transient and steady state performance constraints of dynamic positioning vessel when performing some special tasks,a fault tolerant control strategy with prescribed performance is proposed for dynamic positioning vessel trajectory tracking.By constructing performance function and error conversion unit,the original tracking error system is transformed into a new equivalent system,such that the prescribed performance control problem for the original system is transformed into the stability analysis problem for the new equivalent system.The adaptive control strategy is used to estimate external disturbances and thruster faults,and finally the constraints on transient and steady-state performance of system tracking error are achieved.The simulation results indicate that the proposed method can still ensure the global prescribed performance constraints of the trajectory tracking error in the case of the vessel propulsion system failure,and guarantee the safety of the operation of the fault dynamic positioning vessel.In this paper,aiming at the overdrive dynamic positioning ship with redundant propulsion system,the fault tolerant controller is designed based on the redundancy relationship among the propellers,to ensure that the autonomous fault tolerant control for vessel when happening thruster fault is realized,and the safety and reliability of the vessel operation is further improved.