A fault ride-through strategy for accurate energy optimization of offshore wind VSC[sbnd]HVDC system without improved fault ride-through strategy of wind turbines

Abstract

The transmission of offshore wind power through High Voltage Direct Current (HVDC) systems is an important way to utilization of offshore renewable energy. However, onshore AC grid faults can make it difficult to transmit the energy from offshore wind farms, resulting in HVDC system overvoltages. Existing solutions to this problem mainly include adding DC or AC energy-dissipation devices, adding communication systems, and improving the fault ride-through(FRT) strategy of wind turbines, which have issues with economics or reliability. Based on this, this paper proposes a device-free, communication-free FRT strategy, and the fault ride-through strategy of wind turbines does not need improvement. The exchange of active power between the AC side and DC side of the onshore MMC is calculated under grid-following and grid-forming control strategy. The reference value of DC voltage and offshore MMC capacitance energy are proposed at different control stages. Especially, the dynamically calculated offshore AC voltage reference values have been theoretically provided. This approach ensures that the HVDC system avoids over-voltage and effectively stores more energy. The effectiveness and correctness of the proposed scheme were verified through simulation on the RTDS platFform. This paper is of great significance to promote the development of offshore renewable energy and ensure the safe operation of offshore wind HVDC systems.