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

Area of Science:

• Marine Engineering and Control Systems
• Robotics and Autonomous Systems
• Naval Architecture

Background:

• Dynamic positioning (DP) systems are crucial for marine vessels, but traditional controllers struggle with unknown ship dynamics, unavailable velocity measurements, and unpredictable environmental disturbances.
• Existing DP controllers often require precise knowledge of the ship's dynamic parameters and external forces, limiting their applicability in real-world scenarios.
• Velocity estimation is a significant challenge in DP, as direct measurement is often impractical or unavailable.

Purpose of the Study:

• To develop an adaptive robust output feedback control scheme for dynamically positioned ships.
• To address challenges posed by unavailable velocities, unknown dynamic parameters, and unknown time-variant disturbances.
• To design a controller that relies solely on measurable outputs (position and heading) without prior knowledge of ship dynamics or environmental conditions.

Main Methods:

• A vectorial backstepping method is employed, integrating a high-gain observer and radial basis function (RBF) neural networks.
• The high-gain observer estimates the ship's position, heading, and velocities from available measurements.
• RBF neural networks are utilized to approximate unknown ship dynamics, while adaptive laws with a leakage term estimate RBF weights and disturbance bounds.

Main Results:

• The proposed output feedback controller successfully estimates unavailable velocities and compensates for unknown ship dynamics and environmental disturbances.
• Theoretical analysis using Lyapunov functions proves that the controller ensures all signals in the closed-loop system are uniformly ultimately bounded.
• Simulations demonstrate that the controller can guide the ship's position and heading to an arbitrarily small neighborhood of the desired target values.

Conclusions:

• The developed adaptive robust output feedback control scheme effectively achieves precise dynamic positioning for ships under uncertain conditions.
• The controller's reliance solely on position and heading measurements, without requiring prior knowledge of ship dynamics or disturbances, enhances its practical applicability.
• Simulation results validate the proposed control scheme's effectiveness and robustness in complex marine environments.