Offshore wind energy resources have significant strategic importance, and high-voltage direct current (HVDC) transmission has become the mainstream solution. However, HVDC systems require additional construction of offshore converter platforms, which increases system costs. This paper proposes a low-frequency alternating current (LFAC) transmission scheme combined with a low-frequency auxiliary converter to reduce construction costs and address some of the economic challenges in HVDC systems. A diode rectifier unit (DRU) is used as the rectification station in the LFAC system, which reduces costs and equipment size. However, DRU cannot provide voltage support or starting energy for offshore wind farms. To address this, the paper suggests paralleling a low-frequency auxiliary converter on both the AC and DC sides, which not only provides voltage support for DRU but also delivers starting energy for the wind farm. Additionally, the auxiliary converter can provide reactive power compensation to DRU, eliminating the need for extra reactive power compensation devices. Time-domain simulations confirm the feasibility of the proposed scheme. This study offers new insights for the application of LFAC transmission systems in offshore wind energy development.

Offshore wind farm, diode rectifier unit (DRU), low frequency AC transmission, Auxiliary converter, black start, hybrid voltage-source converter