Ship course-keeping control of marine vessels using dual nonlinear modification strategy

Abstract Aiming at the high energy consumption and severe actuator wear associated with ship heading-keeping control under complex sea conditions, this paper proposes a dual nonlinear modified heading-keeping control algorithm. A second-order nonlinear Nomoto model considering speed reduction is established to better characterize ship maneuvering dynamics. Based on this model, a concise and robust controller is designed using the closed-loop gain shaping algorithm (CGSA). To further improve control performance, a bipolar S-function and a tangent function are introduced to nonlinearly modify the original linear feedback law, forming a dual nonlinear feedback structure. This modification preserves the steady-state performance of the system while enhancing robustness and reducing excessive rudder activity. Simulations are conducted in Simulink using the “ Yukun ” vessel as a case study, where Sea State 6 and Sea State 7 disturbances are modeled by a second-order oscillatory system driven by white noise. Compared with the linear CGSA controller, the proposed method reduces the maximum rudder angle by 31%, the MIA index by 28%, the MTV index by 15%, and the energy index by 51%. The results demonstrate that the proposed strategy can effectively maintain heading stability while significantly reducing control effort and energy consumption, indicating its potential for engineering application.