具有直流故障清除能力的主动接地式模块化多电平换流器

Active-grounded Modular Multilevel Converter with DC Fault Clearing Capability

针对传统半桥型模块化多电平换流器(MMC)无法阻遏故障电流,以及现有具备故障清除能力的MMC故障清除时间过长的问题,提出一种具有直流故障清除能力的主动接地式MMC拓扑。在传统半桥型MMC基础上,在换流器各相上、下桥臂电感外侧增加电流转移支路,在换流器直流出口增加断流支路和能量吸收支路。当MMC直流侧发生双极短路时,断流支路能够有效地隔离断路器和直流线路,电流转移支路能够消耗交流电流和电感电流,能量吸收支路能够快速清除故障电流。文中对主动接地式MMC的拓扑结构及其实现故障隔离和清除的过程进行详细分析,给出了关键参数的设计和计算方法,并利用RT-LAB OP5607软件搭建双端和四端MMC仿真模型,对比分析可知,所提出的主动接地式MMC能够在十几毫秒内清除故障,在经济性和实用性方面具有很大的优势。

In view of the fact that the conventional semi-bridge modular multilevel converter(MMC)cannot block the fault current,and the existing MMC with the fault clearing capability takes too long to clear the fault,an active-grounded MMC(AG-MMC)topology with DC fault clearing capability is proposed.On the basis of conventional semi-bridge MMC,a current transfer branch is added outside the inductors on the upper and lower bridge arms of each phase of the converter,and a cut-off branch and an energy absorption branch are added at the DC outlet of the converter.When a bipolar short circuit occurs on the DC side of the MMC,the cut-off branch can effectively isolate the circuit breaker and the DC line.The current transfer branch can consume AC current and inductor current,and the energy absorption branch can quickly clear the fault current.The topology of AG-MMC and the process of fault isolation and clearing are analyzed in detail,and the design and calculation method of key parameters are given.Finally,the two-terminal MMC and four-terminal MMC simulation systems are built by using RT-LAB OP5607 software.Comparative analysis shows that the proposed AG-MMC can clear faults within ten milliseconds,which has great advantages in terms of economy and practicality.