Fixed-Time Generalized Super-Twisting Controller for the Trajectory Tracking of Unmanned Surface Vehicles in Autonomous Berthing

Autonomous berthing is the last crucial step in achieving full autonomy for unmanned surface vehicles (USVs). It can be transformed into a trajectory-tracking problem. A novel autonomous berthing controller based on fixed-time generalized super-twisting is proposed and the unknown disturbance and model nonlinearity are also considered. First, the fixed-time integral sliding mode surface is designed to solve the inherent singularity problem of long-time convergence. The convergence time is bounded by a constant, independent of the initial conditions. Furthermore, a new generalized super-twisting sliding mode controller is developed and a nonsmooth term is adopted to substitute the generally used discontinuous term to eliminate the chattering. In addition, the stability of the closed-loop system is analyzed and verified by a new Lyapunov function designed. Moreover, the simulations and field tests are conducted to verify its performance. The results show that the control scheme proposed outperforms the comparative control schemes.