A robust nonlinear model-based controller design for a hybrid wave compensation boarding platform for offshore wind farm operation and maintenance

This paper presents a nonlinear extended state observer (NLESO) based nonlinear model predictive controller (NMPC) design for a redundant 9-degree-of-freedom hybrid wave compensation boarding platform for offshore wind farm operation and maintenance to compensate for wave-induced vessel motions. The proposed NLESO is designed to estimate the total disturbance acting on the platform, which arises from unknown variations induced by wind, waves, currents, and the dynamic coupling within the redundant system. First, a task-priority motion planning method dynamically generates the desired compensation trajectory for the hybrid boarding platform to track. Simultaneously, the dynamic model of the hybrid wave compensation platform is transformed into a form suitable for designing the NLESO. Subsequently, the estimated disturbances and the desired compensation trajectory are incorporated into the NMPC to achieve the intended compensation for the platform. The stability of the proposed NLESO based NMPC is analyzed by representing the entire coupled system in the form of a Lure system. Following this, simulation verification demonstrates that, compared to Linear Extended State Observer based Model Predictive Controller (LESO-MPC), Sliding Mode Control (LESO-SMC), and Backstepping Control methods (LESO-Backstepping) under external disturbances, the proposed control strategy achieves lower trajectory tracking errors. Consequently, the wave compensation boarding platform exhibits excellent stability and high control accuracy during coordinated wave compensation tasks.