A combined finite-time speed and yaw controller for an underactuated unmanned surface vessel using way-point navigation

This thesis focuses on the speed and yaw control problem for an underactuated unmanned surface vehicle (USV) with only two propellers navigating through multiple way-points using the line-of-sight (LOS) algorithm. The speed and yaw dynamics are transformed into a cascaded nonlinear system that can be reduced to the stabilization control problem of the surge and yaw subsystems. Both the surge speed and yaw rate controllers are stabilized via finite-time controllers with the surge speed incorporating an acceleration term that uses distance and heading error to vary its speed accordingly when the combination of the error magnitudes call for such change. Comparisons of the traditional stabilization control techniques are made with the proposed finite-time controllers and shown to be inferior to the finite-time controllers in terms of convergence rate and robustness. The stability and effectiveness of the proposed control system is demonstrated and validated by simulation results of a modeled kayak.