一种适用于海上风电经MMC-MTDC并网的电网侧故障穿越方法

海上风电工程逐渐向深远海和多端柔性直流输电技术推进。当岸上交流电网发生故障时，海上风电经多端柔直并网系统应该具有故障穿越的能力。然而现有方法主要研究电网侧换流站的系统级控制策略，未尽限利用风场侧换流站及场站内变流器的协同配合，严重故障时易导致换流站过载。此外，传统两端柔直故障穿越方法未针对多端场景改进，可能会出现风场脱网事故。针对上述问题，首先将故障划分为自消纳和非自消纳场景。自消纳场景下不平衡功率较小，结合风机自身安全减载能力和从站剩余容量，分别提出了基于降压法的超速减载和考虑功率裕度的从站电压偏差下垂控制策略。非自消纳场景下不平衡功率较大，分别提出了调度中心通信正常和异常情况下的故障穿越控制策略。最后在PSCAD/EMTDC仿真平台建模验证了所提控制方法的有效性。

A grid-side fault ride-through method suitable for offshore wind farms connected with MMC-MTDC

Offshore wind power projects are progressively expanding into deep seas and using MMC based multi-terminal direct current (MMC-MTDC). When a fault occurs on the shore AC grid side, the offshore wind farms connected to an MMC-MTDC system should have the capability of fault ride-through (FRT). However, existing methods focus on system-level control strategies between grid side converters, without considering the coordination of other converters. This oversight could lead to converter overload during severe faults. Additionally, traditional FRT methods for MMC based two-terminals have not been adapted for MTDC scenarios. This may result in wind farm disconnection. To address the above issues, faults are categorized into scenarios of self-absorption and non-self-absorption first. The unbalanced power is relatively small in the self-absorption scenario, so this paper proposes an over-speed load-shedding control strategy based on the voltage droop method and a slave station voltage deviation droop control strategy considering the power margin combining safe load-shedding capability of wind turbine itself and slave station surplus capacity. The unbalanced power is larger in the non-self-absorption scenario, so this paper proposes FRT control strategies considering normal and abnormal dispatch center communication. Finally, modeling on PSCAD/EMTDC simulation platform show the validity of the proposed control method.