Research On Fault-Tolerant Control Of Dynamic Positioning Ships With Actuator Faults

With the increasing demand for offshore exploration and marine energy development,as an autonomous control system,dynamic positioning(DP)systems have been widely used in ship operations.The DP system keeps the ship’s position and heading at the desired value by controlling the ship’s own thrusters.During long-term marine operations,the actuators of the ship are inevitably affected by various faults.Therefore,the research on fault-tolerant control of DP ships with actuator faults has theoretical significance and application value.Taking the DP ship as the research object,this dissertation conducts in-depth research and discussion from two aspects:passive fault-tolerant control which not relying on fault detection and isolation(FDI)mechanism and active fault-tolerant control which relying on FDI mechanism.The main research contents are summarized as follows:1.A finite-time passive fault-tolerant control method is proposed for the partial actuator faults of ships without using FDI mechanism.Firstly,the geometric definition of the actuator fault space is described,on the basis of which,the fault severity of the ship’s actuator is analyzed,and the corresponding allowable fault set is given.Then,a novel nonsingular fast integral terminal sliding mode(NFITSM)which has more faster convergence rate is proposed to eliminate the singularity.Secondly,a passive fault-tolerant controller is developed for the partial failure of the actuators of the DP ship,which ensures the fault-tolerant capability for the actuator faults within the allowable fault set.Finally,to reduce the conservatism of the sliding mode controller and ensure the boundedness of control gains,two adaptive laws are designed to automatically update the switching gain of the sliding mode controller.2.A chatter suppression switched passive fault-tolerant controller is proposed for the large range of actuator faults of ships without using FDI mechanism.Firstly,for the state-measurable case,a novel state-dependent hysteresis(SDH)switching logic is designed by selecting a suitable time-varying Metzler matrix.The stability and H-infinity performance of the polytopic switched autonomous system under the SDH switching logic are analyzed,and a sufficient condition in the form of the linear matrix inequality(LMI)for the stability of polytopic switched systems is given.Then,for DP ships,a set of unitary simplex is used to model the actuator fault as a time-varying polytopic switched system,and multiple state feedback controllers are designed according to the LMI conditions.Combined with the proposed SDH switching logic,the resulting switched controller ensures the fault tolerance under a large range of actuator faults.Further,when the states of the system are not measurable,a novel chatter suppression outputdependent hysteresis(ODH)switching logic is designed,and the sufficient condition in the form of the LMI for the stability of the polytopic switched system under the ODH switching logic is also given.Finally,a class of hysteresis switched passive fault-tolerant controller is designed for DP ships,which ensures the stability and H-infinite performance of the closedloop system when the actuator fault occurs.3.For the separated design problem between fault detection and fault-tolerant control,an active fault-tolerant control method based on control allocation(CA)is proposed for DP ships.The proposed control scheme is composed of a high-level controller that creates the generalized forces and a low-level control allocator that distributed the generalized forces among redundant actuators.Firstly,in order to reduce the gain of the controller,a novel double-layer adaptive sliding mode disturbance observer(ASMDO)is designed to estimate the unknown disturbance.Based on the proposed observer,unknown disturbances can be effectively estimated in finite time without the knowledge of their derivative upper bounds.Secondly,a novel prescribed performance function with low-gain characteristics is developed,which imposes priori performance envelops on tracking errors.Subsequently,combined with the idea of the auxiliary intermediate control,an anti-disturbance high-level controller that can simultaneously solve the input constraints and tracking error constraints is designed.Finally,the conservativeness of attainable generalized force set under different distribution matrices is analyzed.Based on linear programming and second-order cone programming,two CA schemes are designed to make sure the generalized forces can be redistributed among the redundant actuators,which solve the problems of actuator saturation constraints and imprecise fault estimation.4.For the integrated design problem between fault detection and fault-tolerant control,in the framework of the supervisory control system,a mode-dependent supervisory switched active fault-tolerant controller is proposed for DP ships.Firstly,the input-to-state stability of nonlinear switched systems under a class of mode-dependent standard conditions and modedependent switching signals is studied,which expands the applicable range of subsystem and reduces the conservativeness of switching signals.On this basis,by properly limiting the switching signal,a class of mode-dependent exponentially weighted integral input-to-state stability is achieved.Further,a class of mode-dependent scale-independent hysteresis(MDSIH)switching logic that considers both the model estimation error and the time scale is designed by applying the above conclusions.The MDSIH switching logic can always switch to the correct controller in a short time interval related to the mode even if the system has an improper hysteresis constant,which is critical for fault-tolerant control.Finally,the design principles of multi-estimator and multi-controller are given for DP ships with different actuator faults.By adopting the designed MDSIH switching logic,the DP system can tolerant the sudden actuator faults while ensuring the boundedness of all signals in the closed-loop system.