基于LCC和FHMMC的混合多端直流系统 线路保护方案研究

混合多端直流线路故障的检测和隔离是一个亟待解决的问题。针对基于电网换相型(Line Commutated Converter,LCC)和混合型模块化多电平换流器(Full Half Bridge Modular Multilevel Converter,FHMMC)的混合多端直流系统拓扑架构,在分析直流线路故障影响的基础上,提出了一种多端直流线路保护方案。首先,通过配置快速线路保护系统,在模块化多电平换流器(Modular Multilevel Converter,MMC)换流器过流闭锁前检测出线路故障。其次,采用在换流站两端配置线路保护系统保护直流线路全长、中间换流站配置线路保护系统分别保护两条线路的配置方案。在此基础上,提出利用线路故障后汇流母线区两侧电流变化量的不同,构造线路故障区域识别判据以解决多端线路故障区域识别问题。最后,通过与控制系统相配合将MMC站直流电压控制为零压或负压,并将LCC站快速移相,实现线路故障的自清除及隔离。仿真结果验证了所提方案的可行性。

Research on protection strategy of a hybrid multi-terminal DC system based on LCC and FHMMC

The detection and isolation of hybrid multi-terminal DC line fault is an urgent problem.In this paper,aiming at the topology structure of hybrid multi-terminal DC system based on Line Commutated Converter(LCC)and Hybrid Half Bridge Modular Multilevel Converter(FHMMC),a multi-terminal DC line protection scheme is proposed.First,by configuring fast line protection system,the line fault is detected before the Modular Multilevel Converter(MMC)is over-currently blocked.Secondly,a configuration scheme is proposed in which the two ends of the converter station are configured with a line protection system to protect the full length of the DC line,and the intermediate converter station is configured with a line protection system to protect the two lines.Based on this,a line fault area identification criterion is constructed using the difference in current changes on both sides of the bus bar area after a line fault to solve the problem of multi-terminal line fault area identification.Finally,in cooperation with the control system,the DC voltage of the MMC station is controlled to zero or negative pressure,and the LCC station is quickly phase-shifted to realize self-clearing and isolation of line faults.The feasibility of the proposed strategy is verified by simulation.