Dual‐Loop Control Design for Dynamic Positioning Ships with Prescribed Performance

Abstract

Dynamic positioning (DP) system is an advanced positioning system widely used in various special operation ships, and the design of control strategies to cope with different constraint conditions is the core technology of DP system research. In this study, a novel dual‐loop control law is proposed to effectively tackle the control challenges encountered by DP ships, particularly in the presence of input saturation and error constraints. Firstly, a saturation handling model is designed to avoid input saturation in the system. Subsequently, a dual‐loop DP control scheme is developed. The outer‐loop is responsible for the ship's position and heading control, while concurrently providing the command velocity signal essential for the inner‐loop. Specifically, a prescribed performance control strategy is designed in the outer‐loop to ensure precise control over positioning errors within predefined ranges and achieve desirable transient and steady‐state performance. The inner‐loop controls the ship's velocity signal, in which a feedback control law is designed based on Hamilton‐Jacobi‐Issacs (HJI) inequality to estimate generalized faults of the DP system. Finally, the proposed control law is validated through numerical simulations on a 76.2 m supply ship, demonstrating superior transient and steady‐state performance compared to existing methods.