Nonlinear control of dynamic positioned ships using only position feedback: an observer backstepping approach

Dynamic positioning (DP) systems for ships are usually designed under the assumption that the kinematic equations can be linearized about a constant yaw angle such that linear theory can be applied. This paper proposes a globally uniformly asymptotically stable (GUAS) nonlinear control law where this assumption is removed. A nonlinear observer is included in the design such that only position measurements are required. GUAS is proven by applying the backstepping design methodology and Lyapunov stability theory The control law is simulated on a thruster controlled ship