Research On Nonlinear Control For Underactuated Surface Vessels Motion

The underactuated surface vessel system is a special kind of nonlinear system with big inertia, strong coupling, certain constraints, and with model parameters uncertainty, time-varying disturbances induced by wind, wave and ocean current. The conventional single nonlinear control method is difficult to achieve the ideal control effect. To overcome these challenges, it has been attracted wide attention from the control community for searching new practical control methods. With the development of marine economy, the requirements of ship steering and offshore oil extraction platform position control are increasing day by day, such as pipeline laying, the dynamic positioning of marine drilling platform, the exploration of marine resources and ocean supply and so on. Therefore, it needs to study the precise control and formation control. The study of control problems for underactuated surface vessel motion possess important theoretical significance and practical value. The main contributions of this thesis are as follows:Firstly, the stabilization problems of underactuated surface vessels are investigated in the presence of uncertain parameters and unmodelled uncertainties including external disturbances and measurement noise. We consider the effect that the rudder generates a lateral acceleration on the sway direction, a two-stage robust adaptive switching control algorithm comprising a manifold convergence controller at the first stage and a sliding mode based stable adaptive neural network controller at the second stage is proposed. Numerical simulations are provided to demonstrate the validity the effectiveness of the proposed control law.Secondly, a nonlinear slding mode controller is presented for trajectory tracking control of underactuated surface vessels; the control law is developed by introducing a first order sliding surface in terms of surge errors and a second order sliding surface in terms of lateral motion tracking errors. The sliding-mode control law can guarantee the position tracking while the rotational motion remains bounded. In this framework, condider the uncertain parameters and time-varying exogenous disturbances, a nonlinear sliding mode adaptive compensation trajectory tracking controller is designed. Numerical simulations are provided to illustrate the effectiveness of the proposed methodology.Thirdly, according to the effect that the rudder generates a lateral acceleration on the sway axis, an output redefined point is introduced to solve the nonminimum phase problem. A novel global sliding mode based trajectory tracking control scheme for underactuated surface vessels is proposed, despite the uncertain parameters and unmodelled uncertainties. Note that a global sliding mode control is presented to design the controller by introducing an integral compensation to eliminate the offset errors. Numerical simulations are provided to validate the effectiveness of the proposed control law.Fourthly, we assume that the sway velocity is passive-bounded, the path following problem is investigated by designing a robust adaptive control strategy to force an underactuated surface vessel to follow a reference path, despite the presence of uncertain parameters and unstructured uncertainties including exogenous disturbances and measurement noise. A virtual vessel is introduced to generate the reference path. According to the uncertain parameters and unstructured uncertainties, a global sliding mode based adaptive NN control strategy is presented. The main contribution is that the controller is designed by integrating a NN approach and a global sliding mode control, and can guarantee the global robustness of the system. The simulation results are presented to verify and illustrate the effectiveness of the proposed controllers.Fifthly, the formation control problem of multiple underactuated surface vessels with the uncertain parameters and unstructured uncertainties is investigated by using the leader-following formation control framework. A global slding mode based robust adaptive control strategy is developed by using the global slding mode control and the adaptive control technique, and an ouput redefined point is introduced to solve the ship course oscillation problem. And then, we consider the leader-following formation framework with unavailable velocity of the leader ship. A global sliding mode formation control scheme is proposed, for only position and heading informations are available from the leader. Numerical simulations studies are also preformed to illustrate the effectiveness of the proposed approaches. Finally, the formation control problem with network induced time-delay, packet-dropout and uncertain parameters is investigated. A global virtual leader vessel is introduced to guarantee the formation stability. A hierarchical formation controller is developed. At the first layer, we use the feedback linearization control method to estabilish a hybrid formation model with parameter uncertainties and communication constraints, and at the second layer, a guaranteed cost dynamic output feedback controller is designed. Simulation examples are shown to demonstrate the performance and effectiveness of the proposed control shceme.