Research On Fault-tolerant Control Methods For Dynamic Positioning Of Ships

As the increasing focus on the exploration and development of the ocean, the deep-seaequipment develops rapidly. The dependence on dynamic positioning system is markedcausing its comprehensive appliance, simultaneously, its security and reliability are requiredstrictly. Control performance must be satisfied in normal dynamic positioning operations,even after occurring fault, some special task must have the ability to continue working withdegraded performance, which insures the system far from serious accident in limited time. Itneeds fault-tolerant control for dynamic positioning of ship which can improve security andreliability of the system.At present, high-level dynamic positioning system of ship all equip physical andanalytical redundancy. With physical redundancy, fault-tolerant control for dynamicpositioning of ship is achieved based on redundancy relationship used by analyticalredundancy, which can ensure durative dynamic positioning operation of ship with fault andhold performance of nominal controller and ability of dynamic positioning of ship. So theresearch of fault-tolerant control method based on analytical redundancy is significative totheory and engineering for dynamic positioning of ship.This paper focused on this frontier subject. Sensor and thruster fault diagnosis method,and sensor and thruster fault-tolerant control method were researched. The fault diagnosismethod based on oriented graph and Support Vector Machine (SVM) was proposed. Thefault-tolerant control method based on virtual sensor with robust sliding mode and virtualactuator with robust adaptive sliding mode were designed.Works achieved in this paper are present as follows.To find the potential fault timely, implement fault-tolerant control for the faulty ship andtruly reflect the ship response characteristics of environmental disturbance and control inputduring the fault-tolerant control process, the3-DOF kinematics and dynamics models of ship,the environmental load model and the propulsion system model were established according tothe literatures. To validate the fault-tolerant control method proposed, the parameters of theship were given.To achieve sensor fault diagnosis for dynamic positioning of ship, binary treeclassification was used to convert multi-classification problem of various fault type to manydimidiate-classifications. The difference method was used to extract feature from the sampling data, then the feature was as the input of SVM. Simulation shows that the methodproposed can achieve the detection of sensor fault quickly and accurately.To achieve thruster fault diagnosis for dynamic positioning of ship, maximum matchingalgorithm from oriented graph theory which can get the structural graph of system was usedto get complete matching between variables and constraints of dynamic positioning ship andpropulsion system. According to the matching, analytical redundancy relation based residualswere designed for constraints of pitch and shaft speed control of each thruster. The faultdiagnosis method based on oriented graph and SVM was proposed, residuals of redundancyrelation were as input of SVM after processing, which make the threshold change with theresult of SVM. The method above can reduce the probability of missing and false alarm,which can insure completeness and improve resolution of fault diagnosis greatly.To achieve fault-tolerant control for dynamic positioning of ship with sensor fault,reconfiguration strategy based on sliding mode observer and virtual sensor technology wasproposed. Virtual sensor was designed to track the state of faulty ship. Virtual sensor isidentical with faulty sensor, which reconfigured control loop of faulty ship from the state ofvirtual sensor. To solve nonlinear, error, disturbance and parameter uncertainties of systemmodel for dynamic positioning of ship, based on sliding mode observer, virtual sensor withrobustness sliding mode was designed to improve the applicability range of virtual sensor.Simulation result shows that the method proposed can well complete the fault-tolerant controlfor the dynamic positioning ship with sensor fault.To achieve fault-tolerant control for dynamic positioning of ship with thruster fault,reconfiguration strategy based on sliding mode control, adaptive control and virtual actuatortechnology was proposed. Virtual actuator was designed between faulty ship and nominalcontroller to reconfigure ship. Virtual actuator is identical with faulty actuator, which makesoutput of reconfigured ship hold the same output feature as nominal ship, insteads ofreadjustment and reconfiguration of nominal controller. To solve nonlinear, error, disturbance,parameter uncertainties and unknown boundary of the uncertainties of system model fordynamic positioning of ship, based on sliding mode control and adaptive control, virtualactuator with robust adaptive sliding mode was designed to improve the applicability rangeand control performance of virtual actuator. Simulation result shows that the method proposedcan well complete the fault-tolerant control for the dynamic positioning ship with thrusterfault.In this paper, with physical redundancy, fault diagnosis and fault-tolerant control fordynamic positioning of ship were achieved by analytical redundancy. Reliability and security of dynamic positioning of ship were improved with standpoint of software, which can providepowerful guarantee compared with physics redundancy indeed.