Research On The Robust Heading Control For AUV Based On Feedback Linearization In Near Surface

AUV (Autonomous Underwater Vehicle) is a typical system which is characterized by nonlinearities, couplings and hydrodynamic uncertainties. It is more difficult to achieve the accuracy heading control for AUV when it navigates near surface under the influences of ocean current and ocean waves. In order to enhance the accuracy, robustness and stability for AUV heading control, a linearization via state feed-back based on geometry theory and the nolinear robust control theory for AUV as well as theirs practical applications are deeply presented and investigated in this paper.Firstly, in order to reduce the system error whose mathematical model of AUV heading control is established based on Taylor linearization technique. The heading control system structure and mathematical models of AUV motion of six degrees of freedom are analyzed in order to perfect the heading control system design model.Then the mathematical model of AUV heading control system which includes hydrodynamic uncertainties and external disturbances are established.Secondly, the linearization via state feed-back method for AUV is presented and deeply investigated to overcome the negative affects of the nonlinearities. For affine nonlinear system, the necessary and sufficient condition for exact linearization of the systems is presented. When uncertainties are considered, the expressions of matching condition and extended matching condition in differential geometry are given. In order to solve the problem of AUV heading control systems with uncertainties, the concept of robust linearization is presented.Thirdly, in order to improve interference suppression for AUV heading control system, such as the influences of ocean current and ocean waves, the nolinear robust control theory and its application are researched. Based on a positive definite solution of Hamilton-Jacobi-Issacs inequality (HJI), A sufficient condition is given such that the closed loop system is asymptotically stable and its L₂ gain is less than or equal to a prescribed value. Using this condition, a state feedback control law which ensured robust performance of the closed-loop system is derived. Due to the difficulty of resolving of HJI inequality, the results are transformed into nolinear matrix inequation for more efficient computation. The nolinear robust controller for AUV heading control is designed based on the state of the nonlinear feedback linearization method.Lastly, the nolinear robust controller for AUV heading control system is applied to the AUV virtual simulation platform, obtaining the heading control curves under the different simulation environment of AUV.The simulation results fully demonstrate that the nonlinear robust controller can improve the dynamic characteristics and robustness than the standard robust H_∞, controller in a certain extent.