Hybrid-mode Offshore Hydrogen-producing Wind Turbine: Grid-following and Grid-forming Operation Under Variable Grid Conditions

This paper proposes a hybrid-mode operation strategy for an offshore hydrogen-producing wind turbine (OHP-WT) capable of grid-following (GFL) and grid-forming (GFM) operation under both normal and low-voltage ride-through (LVRT) conditions. Unlike conventional centralized wind-to-hydrogen (W2H) schemes, the proposed turbine-level architecture integrates W2H converters directly into the DC link of a three-level neutral-point-clamped converter. A supervisory power-sharing and mode-switch layer is developed above established GFL and GFM controls to coordinate active and reactive power regulation, DC-link balancing, and hydrogen-load management according to grid conditions. The proposed strategy is validated through detailed PLECS simulations and real-time hardware-in-the-loop experiments using identical parameters. Results show that the GFL mode achieves accurate power dispatch and shallow-fault LVRT compliance, while the GFM mode maintains voltage and frequency stability under weak grid and severe-fault conditions. In all cases, maximum-power-point tracking (MPPT) is preserved, and hydrogen production continuously absorbs surplus power to stabilize the DC link. The findings demonstrate that the hybrid-mode OHP-WT enables transition between grid support and hydrogen production, effectively reducing wind-power curtailment and enhancing offshore grid resilience.