| Oceans make up a greater portion of the earth surface.Land resources are far less abundant than marine resources,but the marine environment is more complex and thus much more difficult to explore than the land environment.Nowadays,the demand for land resources exceeds the supply,thus mankind gradually move the platform of resources exploitation to the sea.However,the marine environment is very complex,especially in the deep and open sea,the exploitation of seabed resources is quite difficult.Therefore,the requirement of robustness for Dynamic Positioning(DP)vessel is getting higher and higher.DP vessels will face many practical constraints such as propulsion system failure、input saturation when operating in harsh marine environments.To address this problem,focusing on constraints such as ship input saturation,model uncertainty,and thruster failure,a more comperhensive robust fault tolerant scheme was proposed in this paper.The main work accomplished in this paper is as follows:First,establish the mathematical model of the vessel on the basis of the established coordinate system,and then establish the thruster failure mathematical model to address the thruster failure problem,at the same time,summarize relevant theories and analyze its design methods.The above mathematical models are simulated and verified on the basis of the research object.Secondly,an adaptive backstepping and integral nonsingular fast terminal sliding mode control(ABINFTSMC)scheme is proposed for the trajectory tracking and positioning task of the DP vessel with input saturation and actuator failure.There are various sliding mode control varieties which feature different advantages.For instances,integral sliding mode makes the system state on the sliding mode surface at all times,and improves the robustness of the system.Terminal sliding mode could converge to the expected trajectory in finite time,and the nonsingular performance can solve the singular problem in the terminal sliding mode.Therefore,it integrates the advantages of integral sliding mode and that of nonsingular fast terminal sliding mode,in order to enable the dynamic positioning vessel suffering propeller failure to fulfill the scheduled trajectory tracking task.The saturation function method is adopted to solve the problem of input saturation.Meanwhile,the lower bound of the fault information and unknown upper bound of the disturbance are estimated online through the adaptive mechanism.Then puts forward the adaptive integral nonsingular fast terminal sliding mode control scheme.At last,on the basis of the backstepping method and Lyapunov stability theory,the analysis on stability is conducted to verify the effectiveness of controller designed by this paper through simulation analysis.Finally,an adaptive neural network backstepping and nonsingular fast terminal sliding mode control(ARBFNNBNFTSMC)scheme is proposed for the trajectory tracking task of the DP vessel with input saturation、actuator failure and model uncertainty.Based on the control plan of adaptive backstepping integral nonsingular fast terminal sliding mode,the BF neural network control featuring the best approximation performance,learning process and fast convergence speed as well as the adaptive technology,it solves the problems of propeller failure,time-varying disturbance and model uncertainty.The neural network is used to fit the comprehensive uncertainty in the article,and the approximation error of the neural network is adjusted by adaptive technology.By doing so,it enables the dynamic positioning vessel to fulfill the scheduled trajectory tacking task in case of propeller failure,model uncertainty and input saturation and realize fast convergence in finite time without chattering,which guarantees the steady-state performance and transient performance of the system.On the basis of the backstepping method and Lyapunov stability theory,the analysis on stability is conducted to verify the effectiveness of controller designed by this paper through simulation analysis. |
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