Research On Stabilization Control Of Underactuated Surface Vessels

The underactuated system means that the number of independent control variables is less than the number of degrees of freedom system, simply, the number of input is less than the number of control. Underactuated system, not only can reduce the cost and the weight of the control equipment. In the real cases, the idea of underactuation can be used to control systems in which some components are failed during operation so that the system is also be controlled by the unfailed components effectively and the influence on the system performance caused by failure of system components can be decreased. So, the more and more attention has been paid to the underactuated mechanical system in recent years.The focused object is surface vessel, under certain assumptions, the system is underactuated. So for the different control aims, the problem on nonlinear control of the underantuated surface vessel is focused. Dynamic mathematical model of ship motion is established, and thus the three degree of freedom model of underactuated surface vessels is simplified. The underactuated surface symmetry of ship model is considered, this means in the mathematical model that the non-diagonal elements that in the matrix of inertia parameters and the matrix of damping are zero. The mathematical model of underactuated surface vessel is divided into two subsystems, as long as one of these subsystems can gradually stability, we can prove that the system can also be asymptotically stable.The stabilization problem of an underactuated symmetric surface vessel is investigated. First of all, based on the global diffeomorphism and time-varying coordinate transformation, the ship dynamic system can be decoupled into two linear subsystems, and the stabilization problem of the original system is changed into the stabilization problem of the subsystems. Second, a global K-exponential stabilizing controller for the two subsystems is constructed for the ship in consideration.Finally, the result are simulated, proving that designed controller can make the system stabilization to the origin.