Robust global asymptotic position stabilization for uncertain underactuated surface vessels without velocity Measurement

Global asymptotic stabilization problem of underactuated surface vessels has been so far considered not only by designing complicated nonlinear control law, but also by requiring the velocity feedback or the known model parameters. This paper proposes a simple robust proportional (P) position stabilization static control law for underactuated surface vessels with unknown model parameters, which takes a simple linear form excluding velocity feedback, observer and adaptive law. A novel nonnegative function is for the first time constructed, together with Lyapunov direct method and Barbalat's lemma, showing that the proposed control law guarantees the position error and velocity variables globally asymptotically convergent to zero. The effectiveness of the proposed control scheme is demonstrated by the simulation example.