Abstract
Low-frequency transmission technology has become a highly competitive method of power transmission in the scenario of offshore wind power delivery in the medium and long sea areas. The low-frequency power transmission line has a permanent magnet synchronous generator (PMSG) on one side and a modular multilevel matrix converter (M3C) on the other side. However, when a fault occurs in the low-frequency power transmission line, its fault characteristics are determined by the converters on both sides, which is fundamentally different from the conventional synchronous machines. Additionally, the capacitive current issues brought about by long submarine cables should not be overlooked, traditional AC protection has revealed adaptability issues, and low-frequency line protection faces new challenges. This paper introduces the topology and control strategy of offshore wind power transmitted through low-frequency transmission system(LFTS), then the challenges faced by protection after faults on low-frequency transmission lines were analyzed. In response to the decline in the performance of traditional AC protection, a flexible low-frequency transmission line protection for offshore wind power based on Canberra distance is proposed. Finally, a flexible low-frequency transmission system model for offshore wind power was built in PSCAD/EMTDC, and the simulation results show that: the proposed protection scheme can correctly operate under various fault conditions and has certain resistance to transient resistance and anti-interference capabilities.