Nonlinear output feedback control of dynamically positioned ships using vectorial observer backstepping

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 and gain scheduling techniques can be applied. This paper proposes a globally exponentially stable (GES) nonlinear observer is included in the design such that only position measurements are required. GES is proven by applying the backstepping design methodology and Lyapunov stability theory. The control law is simulated on two thruster-controlled ships.