Offshore AC Fault Ride-Through for Grid-Forming Offshore Wind Farms Connected Through LCC-HVdc Links

Line-commutated converter (LCC) is a promising choice for integrating large offshore wind farms. In such a system, grid-forming (GFM) control for wind turbine converters is necessary for establishing the offshore ac grid. However, during severe offshore grid ac faults, the GFM converter is susceptible to overcurrent and transient synchronization stability issues, given its internal voltage source nature. In this study, the offshore ac fault ride-through (FRT) issue is studied for the LCC-HVdc connected offshore wind farms. A unified model for the transient synchronization analysis considering current limiting is proposed. On this basis, key new factors, including current limiting and low emulated inertia are revealed to have detrimental impacts on the reliable FRT. A FRT strategy is proposed to address this problem, and simulations validate the feasibility of the method.