The Research Of Variable Structure Control Technology Of Autonomous Underwater Vehicle Navigating Near Surface

Autonomous Underwater Vehicle (AUV) is a typical system which is characterized by high nonlinearities, couplings and uncertainties. In general, it is difficult to get its precise dynamic model. The motion of AUV changes obviously when it navigates near surface under the influence of ocean waves. The hydrodynamic effect becomes more complicated and the nonlinearity of its motion becomes more notable. The AUV will float up to the surface and finally floats out of the surface under the influence of the second-order wave forces. So it is difficult to sustain the depth.As an integrate control method, the merit of Variable Structure Control (VSC) method lies in that it can use imprecise mathematical models to design the controller. Besides, the design of sliding side is insensitive to uncertainties including parameter variations and external load disturbance. So it is suitable to control the movement of AUV's navigating near surface.This dissertation aims at the application of VSC to the motion control of AUV's navigating near surface, and trying to design a control system which performs better. Firstly, dynamic model of AUV with 6 degrees of freedom is properly simplified for the need of practice. Wave forces are calculated numerically through wave spectrum and simulation research is carried out when the AUV navigates near the surface. Then a kind of VSC problem of controllable regular nonlinear system is researched in this dissertation. For the controllable regular multi-input nonlinear system, a decentralized control strategy is selected and the system is changed into the linear reductional form. The pole setting method is used to design the switching function. In order to eliminate chattering, the tendency ration strategy and the slippery function method is used. Besides, an integrator is added to the controller to reduce the steady-state error under the wave disturbances. Finally, simulation experiment is carried out at two situations: in deep ocean without wave disturbances and near surface with wave disturbances. Simulation results show that the controller presented in this dissertation provides high performance dynamic characteristics and anti-jamming ability. Also it is validated that the Integral VSC method is suitable and effective for the motion control of AUV's navigating near surface.