Adaptive Robust Output Feedback Control for a Marine Dynamic Positioning System Based on a High-Gain Observer

TLDR

The study proposes an adaptive robust output‑feedback controller for dynamically positioned ships that operates without velocity measurements or prior knowledge of ship dynamics and environmental disturbances. The controller combines a high‑gain observer to estimate position, heading, and velocities with radial‑basis‑function neural networks in a vectorial backstepping framework, and employs adaptive laws with leakage to learn the network weights and disturbance bounds. Theoretical Lyapunov analysis shows the controller drives ship position and heading arbitrarily close to desired targets while keeping all signals bounded, and simulations with two ships confirm its effectiveness.

Abstract

This paper develops an adaptive robust output feedback control scheme for dynamically positioned ships with unavailable velocities and unknown dynamic parameters in an unknown time-variant disturbance environment. The controller is designed by incorporating the high-gain observer and radial basis function (RBF) neural networks in vectorial backstepping method. The high-gain observer provides the estimations of the ship position and heading as well as velocities. The RBF neural networks are employed to compensate for the uncertainties of ship dynamics. The adaptive laws incorporating a leakage term are designed to estimate the weights of RBF neural networks and the bounds of unknown time-variant environmental disturbances. In contrast to the existing results of dynamic positioning (DP) controllers, the proposed control scheme relies only on the ship position and heading measurements and does not require a priori knowledge of the ship dynamics and external disturbances. By means of Lyapunov functions, it is theoretically proved that our output feedback controller can control a ship's position and heading to the arbitrarily small neighborhood of the desired target values while guaranteeing that all signals in the closed-loop DP control system are uniformly ultimately bounded. Finally, simulations involving two ships are carried out, and simulation results demonstrate the effectiveness of the proposed control scheme.