Research On Motion Control For Underactuated AUV Based On Non-smooth Method

Autonomous underwater vehicle(AUV)has always been a hot topic in marine research.The AUV has the ability to complete underwater operations independently and has a wide range of applications in marine exploration,ocean mapping,underwater pipeline inspection and military field.Due to the advantages of the underactuated AUV in reducing the weight of the system,saving manufacturing costs and reducing energy consumption,it is of great practical significance to study the motion control of the underactuated AUV.This study is carried out with the underactuated AUV as the research object,aiming at the point stabilization problem and the trajectory tracking control problem in the horizontal plane and the three-dimensional trajectory tracking control problem.The controllers are designed based on non-smooth method to realize the corresponding control objectives.To the point stabilization problem of the underactuated AUV in the horizontal plane,non-smooth controllers based on adding a power integrator approach are designed in this paper.Firstly,the limitations of Brockett's necessary conditions are avoided by the coordinate transformation of the polar coordinate.Secondly,the transformed system is divided into the heading and distance subsystems by using variable substitution.Thus the high-order system is transformed into two low-order systems.Then,two controllers are designed for the two subsystems by using adding a power integrator approach,respectively.Finally,the controller is designed for the case the starting point coincides with the target point by using adding a power integrator approach.By constructing appropriate Lyapunov functions,it is proved that the velocities,distances and angle of an underactuated AUV can converge to the desired values.Simulation results demonstrate the effectiveness of the proposed control method.To deal with the trajectory tracking control problem of the underactuated AUV in the horizontal plane,a controller is designed based on the nonsingular fast terminal sliding mode.Firstly,the trajectory tracking error system is established according to the kinematic equation and dynamic equation of the underactuated AUV.Secondly,the desired velocities are designed to ensure that the position tracking errors can converge to zero asymptotically,and the limitation of the desired velocities obtained by deriving the desired positions is avoided.Then,the nonsingular fast terminal sliding mode is used to design the longitudinal thrust and the yawing moment,so that the desired velocities of the underactuated AUV can be tracked in finite time.Finally,numerical simulations are conducted to verify the effectiveness of the controller.The results show that the underactuated AUV can track the desired trajectory in the horizontal plane by the proposed controller.To deal with the three-dimensional trajectory tracking control problem of the underactuated AUV,a non-smooth controller is designed based on adding a power integrator approach.Firstly,the trajectory tracking error system is established based on the kinematic equation and dynamic equation of underactuated AUV.Considering the complex nonlinearity of the three-dimensional model and the coupling between the degrees of freedom,the trajectory tracking error system is represented as a cascade system of position errors and velocity errors by designing desired velocities.Then,the controller is designed for the trajectory tracking error system by using adding a power integrator approach.Finally,the stability of the closed-loop system is proved based on the finite-time Lyapunov stability theorem.The numerical simulation results show that the underactuated AUV can track the desired three-dimensional trajectory in finite time.