基于电压电流突变量的MMC-MTDC纵联保护方案

作为柔性直流输电线路后备保护的纵联电流差动保护，通过较长延时来防止线路分布电容等问题引起的误动，无法满足保护对于速动性的要求，针对这一问题提出了一套基于电压电流突变量夹角余弦值的纵联保护方案。该方案利用故障发生时，故障与非故障状态下直流线路两端的电压、电流突变量之间的夹角余弦值构造故障识别判据，并利用故障发生时线路正、负极电压的数值差异作为故障极判据，形成了一套完整的纵联保护方案。最后，在PSCAD/EMTDC平台上搭建了基于模块化多电平换流器的多端柔性直流输电（modular multilevel converter-multi-terminal direct current，MMC-MTDC）系统仿真模型对保护方案进行验证，结果表明，所提纵联保护方案能够实现在各种故障情况下的故障判别，并且满足直流线路对保护速动性的要求，可以作为直流线路的后备保护。

MMC-MTDC Pilot Protection Scheme Based on Voltage and Current Mutation

As the reserve protection of the DC transmission line, the longitudinal current differential protection prevents the unwanted operation caused by distributed capacitance by the long delay and the requirement for quick action of the protection cannot be satisfied. This paper proposes a pilot protection based on the cosine of angle difference between the voltage and current mutations. The fault identification criterion is constructed by the cosine of angle difference between the voltage and current mutations. And the difference between the positive and negative voltages is used to identify the fault pole. Finally, a four-terminal MMC-MTDC simulation model is built on the PSCAD/EMTDC platform to verify the protection scheme. The results show that the proposed scheme can realize fault identification under various fault conditions and meet the requirement of fast protection, and can be used as the reserve protection of DC transmission lines.