Fault-Tolerant Control For Dynamic Positioning Ships Via Integral Sliding Mode Output Feedback Technique

Dynamic positioning(DP)ships are widely used in marine pollution cleanup,environmental monitoring,oil development,scientific exploration and other fields due to its advantages of being unrestricted by water depth,precise positioning and high mobility,which has become one of the important tools for ocean exploration and development.However,the thrusters of DP ships inevitably fail in the complex and variable marine environment,which may result in task cancellation.Meanwhile,the phenomenon of signal quantization,input quantization mismatch and unknown parametric dynamics will also affect the stability of DP ships control system.On the other hand,the integral sliding mode output feedback method is widely used in the design of control system because it can ensure the robustness of the system from the initial time by only using measurement information.Considering the above-mentioned factors,this paper mainly studies the robust fault-tolerant control strategy by using the integral sliding mode output feedback technology.The main results of this thesis are as follows:(1)This paper proposes a fault-tolerant control method based on integral sliding mode output feedback control for DP ships in the presence of unknown ocean disturbances and thruster faults.Firstly,a full order dynamic compensator is constructed using the measurable outputs to introduce some degrees of design flexibility,and an integral sliding mode surface is designed based on compensator state and output information.Then,by using adaptive mechanism and matrix full-rank decomposition,an integral sliding mode output feedback controller is designed to attenuate the oscillation amplitudes of the yaw angle and yaw velocity error from the beginning time in the presence of thruster faults and ocean external disturbances.Finally,through a typical floating production ship,the effectiveness of the proposed method is verified in the simulation example.(2)This paper proposes a fault-tolerant control scheme based on quantized integral sliding mode control for DP ships with thruster faults,signal quantization and disturbances.First,based on the quantized signals of system output,an integral sliding manifold and a dynamic compensator are constructed.Then,design an integral sliding mode output feedback controller,and a novel dynamic quantization parameter adjustment strategy is proposed.Compared with the existing results,the relation between the attraction area and quantization range is revealed for the first time.The stability analysis results show that the closed-loop stability can be guaranteed from the every beginning time in despite of the quantization and thruster faults.Finally,simulation results verify the effectiveness of the proposed method.(3)This paper proposes a fault-tolerant control scheme based on integral sliding mode output feedback for DP ships where input quantization mismatched phenomenon is considered.The mismatched relation between quantization parameters at encoder and decoder sides involves the controller design conflicts which might induce instability of DP ships in practice.To tackle this problem,a time-varying ratio model with unknown lower and upper bounds is established,and adjusted online through linear differential equations,which avoids the complicated nonlinear updated laws in the existing literature.Furthermore,the fuzzy logic systems are employed to approximate the unknown nonlinear functions,then an integral sliding mode control law is designed to guarantee the stability of DP ships in spite of input quantization mismatch and thruster faults.Finally,simulation results verify the effectiveness of the proposed control technique.(4)This paper proposes an integral sliding mode output feedback fault-tolerant control scheme for DP ships where unknown parametric dynamics is considered.First,an integral sliding surface based on a high gain compensator and output information is constructed.Then,an adaptive technique is used to estimate the upper bounds of unknown faults and disturbances.Based on this,an integral sliding mode controller is designed,and the relation between an attraction region and dynamic uncertainties is revealed for the first time.The closed-loop stability can be guaranteed from the every initial time in despite of thruster faults,unknown parametric dynamics and unknown marine environmental disturbances.Finally,simulation results verify the effectiveness of the proposed method.