基于超级电容储能的大容量直驱风电机组低电压穿越策略

模块化多电平换流器(modular multilevel converter, MMC)可用作大容量风电机组的换流器，其具有良好前景，但需要解决风电机组低电压故障时易脱网运行的问题。鉴于此，提出了一种基于超级电容储能的低电压穿越策略。考虑超级电容的利用效率和变流器的约束条件，通过DC-DC变换器对超级电容的储能模式进行控制，实现故障期间机、网侧的功率平衡，以稳定直流侧母线电压。按照海上风电场规定，确定了故障期间网侧MMC有功无功电流分配原则，向电网提供动态无功以帮助恢复电网电压。仿真结果表明，当并网点发生故障时，所提策略不仅能较好地稳定直流母线电压，保障了MMC功率器件安全运行，还可以补偿无功以改善电网电压，提高了大容量直驱风电机组的故障穿越能力和运行稳定性。

Low voltage ride-through strategy for high-capacity direct-drive wind turbines based on supercapacitor energy storage

The modular multilevel converter (MMC) is a promising prospect as a high-capacity wind turbine converter, but it is necessary to address the issue of easy disconnection during low voltage faults in wind turbines. Thus a low voltage ride-through strategy based on supercapacitor energy storage is proposed. Considering the utilization efficiency of supercapacitors and the constraints of converters, the energy storage mode of supercapacitors is controlled through DC-DC converters, achieving power balance on the machine and network sides during faults and stabilizing the DC bus voltage. From the regulations of offshore wind farms, the active and reactive current distribution principles of a grid-side MMC during faults are determined. This can provide dynamic reactive power support to improve grid voltage. Simulation results show that the proposed strategy can effectively stabilize the DC bus voltage during grid faults, ensure the safe operation of MMC power devices, compensate reactive power to improve grid voltage, and enhance the fault ride-through capability and operational stability of large-capacity direct-drive wind turbine generators.