直流配电网中的线路保护方案研究

故障区段的可靠识别是直流配电网线路保护的难点之一,由此产生相邻线路保护的配合问题,并需防止交流故障后直流保护误动。基于平波电抗器和滤波电抗构成的物理边界的故障区域识别方法,不适用于采用模块化多电平换流器(Modular multilevel converter, MMC)的直流电网。为此,在分析直流线路短路的电气特征后,综合考虑保护配合问题,划分了直流线路保护区域,设计了包含主保护、后备保护在内的直流线路保护方案。为满足选择性要求,直流线路保护采用两端电流方向判断故障位置。最后,搭建光伏直流汇集接入系统及多端直流配电网的仿真模型,验证了该直流线路保护方案的可靠性、选择性和速动性。

Line protection scheme for DC distribution grids

The reliable identification of the fault zone is one of the bottlenecks in the DC line protection of a distribution network, which results in the issue of the cooperation between adjacent line protections, as well as preventing DC protections from malfunction after AC faults. The existing faulted-zone identification methods, which relys on the physical boundary formed by smoothing and filtering reactors, are not applicable for DC grids based on the Modular Multilevel Converter (MMC). Therefore, after analyzing fault characteristics of the DC line and considering the cooperation between protections, the DC line protected zones are divided, and the DC line protection scheme, consisting of the main protection and backup protection, is designed. To implement the selectivity, both-terminal current direction information of the protected line is employed to determine the fault location. Finally, the reliability, selectivity and rapidity of the proposed DC line protection are verified by means of the simulation model of a PV integration system and a multi-terminal DC distribution network. This work is supported by National Natural Science Foundation of China (No. 51877084), Natural Science Foundation of Hebei Province (No. E2018502063), and Science and Technology Project of Hebei Electric Power Company (No. kj2017-008).