基于混合型Chopper电路的MMC-UPFC故障渡越方案

Fault ride through scheme of MMC-UPFC based on hybrid Chopper circuit

当交流系统发生短路时,基于模块化多电平控制器的统一潮流控制器(MMC-UPFC)串、并联侧MMC均会受到故障冲击,存在两侧换流器过流闭锁,MMC-UPFC完全退出运行的风险。对此,以交流系统发生最严重的三相短路故障为例,分析了MMC-UPFC串、并联侧MMC故障特性;在此基础上,借鉴风电场交流故障渡越的Chopper电路,并结合MMC-UPFC不同运行方式对故障特性的影响,提出了基于混合型Chopper电路的MMC-UPFC故障渡越方案。该方案能够在交流系统发生故障后隔离并联侧MMC与串联侧MMC之间的联系,从而抑制串联侧馈入并联侧MMC的故障电流。仿真结果表明在MMC-UPFC的不同运行方式下,所提方案均能避免故障后并联侧MMC闭锁,MMC-UPFC将切换至静止同步补偿器(STATCOM)工作模式,为交流系统提供无功功率支撑。

The MMC-UPFC(Modular Multi-level Converter based Unified Power Flow Controller)will suffer fault impact in both series side and shunt side when a short circuit occurs in its AC system,leading to over-current blocking of MMCs in both sides and the risk of MMC-UPFC out of service.Taking threephase short circuit fault as an example,the fault characteristics of MMCs on both series and shunt sides are analyzed.On this basis,a fault ride through scheme of MMC-UPFC based on hybrid Chopper circuit is proposed with referring to Chopper circuit in wind farm AC fault ride through,as well as combining with the effects of different MMC-UPFC operation modes on fault characteristics.The proposed scheme can isolate the connection between the shunt side MMC and the series side MMC after fault occurs,so as to suppress the fault current fed from the series side into shunt side MMC.Simulative results show that the proposed scheme can avoid the blocking of shunt side MMC under different MMC-UPFC operation modes,and the MMC-UPFC can serve as static synchronous compensator and provide reactive power to AC system.