State-dependent trajectory planning and tracking control of unmanned surface vessels

A new method combining trajectory planning, tracking and coordinated control for unmanned surface vessels is presented based on nonlinear sliding mode control. A limiting factor of sliding mode tracking control is that it can only guarantee position tracking as long as the vessel initial conditions are on the desired trajectory. In this work, a transitional trajectory between the vessel initial condition and the desired trajectory path is implemented using a set of two ordinary differential equations (ODEs) in terms of the position state feedbacks such that the ODE solution converges to the desired trajectory path. An additional advantage of this approach is that when the ODE represents a limit cycle, it can be used for coordinating multiple vessel trajectories without any possibility of collision. Several simulations are presented where the vessel successfully reaches and follows a desired trajectory starting from a variety of initial starting conditions.