Path Following of an Underactuated Autonomous Underwater Vehicle Using Backstepping and Disturbance Observer-Based Sliding Mode Control

In this paper, a new hierarchical robust nonlinear control scheme is designed for the horizontal plane path following control problem of an underactuated autonomous underwater vehicle in the presence of the model uncertainties and fast-time-varying external disturbances. First, the path following error model is established based on the virtual guidance method. Afterwards, the controller design starts at a kinematic level and evolves to a dynamic setting, building on the kinematic controller derived, using backstepping technique and a disturbance observer-based sliding mode control, respectively. A Lyapunov-based stability analysis proves that all the signals are ultimately bounded, and path following errors converge to an arbitrarily small neighborhood of the origin. Following achievements are highlighted in this paper: (I) in order to simplify the control design, the derivative of the virtual control is estimated by the disturbance observer which avoids explosion of complexity without common filtering techniques; (II) the proposed controller can be easily implemented with no information of the bounds on the parameter uncertainties and external disturbances in a continuously changing environment. Furthermore, computer simulations have shown that the overall closed-loop system achieves a good path following performance, which proves the feasibility and good robustness of the proposed control law.