Control Study Of Ship Power Positioning System Under Time Lag And Uncertainty Environment

Ship power positioning system is a kind of system used to control ship positioning and maintain stability at sea,which is widely used in the fields of marine engineering,marine scientific research and sea rescue,etc.It can improve the operation efficiency and safety of ships and reduce the dependence on crew and the need for human operation.Therefore,it is of great significance to conduct in-depth research on ship power positioning control system.However,in the actual marine environment,problems such as measurement system failure or delayed transmission time lag,actuator response time lag and model uncertainty of the ship appear,which can make the system control performance deteriorate and lead to phenomena such as slow convergence speed,overshoot and large oscillation of the ship during positioning,thus bringing challenges to the design of the power positioning control system.This thesis addresses these problems in depth in order to further improve the positioning accuracy and stability of the ship.Firstly,based on the kinematics and dynamics analysis of the ship,a six-degree-offreedom mathematical model of the ship is established,and the low-speed characteristics and influencing factors of the ship motion are considered and simplified to a three-degree-offreedom mathematical model,and the ship with actuator time lag is modeled on the basis of this model.In addition,a mathematical model of marine environment disturbance is also established.Secondly,for the situation of ship disturbance and actuator time lag,the backstepping controller and sliding mode controller based on Lyapounov-Krasovskii function are designed and simulated and compared with the traditional backstepping and sliding mode controllers,respectively,and the results show that both controllers can effectively suppress the influence of ship actuator time lag.Among them,the sliding mode controller based on LyapounovKrasovskii function acts with higher positioning accuracy and smoother convergence process,but the convergence time is longer.The backstepping controller based on the LyapounovKrasovskii function has a relatively low positioning accuracy and slight overshoot,but the convergence response is faster.Then,a mathematical model of time lag and uncertainty for power positioning ships subject to measurement system failure or delayed transmission time lag,actuator response time lag and uncertainty is established,and an adaptive backstepping sliding mode controller based on Lyapounov-Krasovskii function and RBF neural network is designed by combining the respective advantages of sliding mode and backstepping method;meanwhile,the NARX neural network model is used to predict the output of the measurement system with time lag,a compensation function is constructed to compensate for the prediction error,and the predicted position value is input to the controller as feedback.And the simulation is compared and verified in the states of no time lag,with uncertainty and with time lag,with uncertainty,respectively.The results show that the adaptive backstepping sliding mode controller based on Lyapounov-Krasovskii function and RBF neural network combined with NARX prediction model has higher localization accuracy and faster response speed,smooth convergence process without overshoot and oscillation,and stronger suppression effect on time lag and uncertainty.Finally,in order to verify the effectiveness of the above designed controller,a semiphysical simulation model of ship power positioning control system is designed.The overall design of the ship power positioning system is carried out,and the hardware system of the semi-physical simulation model is built.Then the software of the positioning control system is designed according to the above control algorithm,and the data sending and receiving and positioning functions between the upper computer and the lower computer are realized.