Horizontal Trajectory Tracking Control Of An Underactuated UUA With Input Delay

In recent years,the Unmanned Underwater Vehicle(UUV)has become an important tool for the exploration and development of marine resources,and it has been highly valued by marine researchers at home and abroad.UUV motion control technology is an important technical support for UUV to successfully complete all kinds of underwater operation tasks UUVs are usually under-actuated,and the model have strong coupling,high nonlinearity and parameter uncertainty.In addition,the interference of the external environment and the time delay of the actuator make UUV trajectory tracking control more difficult to achieve.So this paper takes under-actuated UUV as the research object to solve the problem of UUV horizontal trajectory tracking control with input delay,external unknown environmental disturbance and parameter perturbation.The main research work is as follows:Firstly,the 3-DOF kinematics and dynamics model of under-actuated UUV horizontal plane is established.The characteristics of strong nonlinearity,high coupling,input delay,parameter uncertainty and external environmental interference of UUV mathematical model are analyzed.verify the accuracy of the established model through simulation experiments on the horizontal and rotary motion of the UUV model.Secondly,in the case of time-delay of actuators such as underactuated UUV rudders and propellers,a trajectory tracking backstepping controller based on state prediction is designed for the problem of the horizontal trajectory tracking.The method is based on the backstepping method to design the trajectory tracking controller.According to the dynamics and kinematics model of UUV,the velocity and pose predictor are respectively established.The influence of the input delay on the system is suppressed by predicting the future state.Aiming at the external environment interference,a nonlinear disturbance observer is designed and fedback the estimate to the controller,which effectively suppresses the disturbance.Aiming at the problem of "differential explosion" caused by the direct reference to the virtual control quantity in the traditional backstepping design,three first-order low-pass filters are introduced,and the integral operation is used instead of the differential operation to obtain the first derivative of the virtual control variable,avoiding Direct derivation of the amount of virtual control.Thirdly,aiming at the UUV horizontal trajectory tracking control problem with input delay,model uncertainties and external unknown environmental disturbance constraints,a UUV trajectory tracking controller combining backstepping method and sliding mode method is designed.Firstly,the model parameter uncertainty and environmental disturbance are regarded as compound disturbances.The disturbance is estimated by RBF neural network algorithm,and the composite disturbance estimation value is fed back to the controller to offset its influence on the system.Secondly,the backstep method is applied.In the kinematic loop,a virtual speed controller is designed to stabilize the position error.Thirdly,the Integral sliding mode method is used to design the actual control law to stabilize the virtual speed error.Finally,the state predictor is designed to predict the future state.Forecast to suppress the impact of input delay on the system.Finally,in order to verify the effectiveness of the underactuated UUV horizontal trajectory tracking backstepping controller and the backstepping-sliding mode controller,two sets of simulation comparison experiments were carried out before and after the state predictor was added.The simulation results show that the trajectory tracking controller control based on state prediction design can greatly improve the robustness of the control system,not only the control performance is good,but also can effectively suppress the influence of input delay on the system.