MMC拓扑无变压器并网存在的问题和解决措施

Existing Problems and Solutions to MMC Topology without Grid Integration of Transformer

适用于城市电网的柔性直流换流器拓扑需要考虑可靠性、经济性、占地和故障特性。柔性直流换流器不通过变压器而直接接入10 kV交流电网带来2个问题:当直流侧发生单极接地故障时,交流侧断路器无法正常分闸;直流侧双极短路电流大。通过理论分析和仿真验证了桥臂串联阻尼模块的MMC拓扑具有交流侧故障穿越和直流侧故障抑制能力,可较好解决上述问题,满足城市电网对柔性直流换流器拓扑的要求。

VSC-HVDC converter topology applicable to urban power grid must take reliability,economy,land occupation and failure characteristics into account.The integration of VSC-HVDC converter into 10 kV AC power grid without transformer faces two problems:first,the breaker at AC side cannot be switched normally in the case of unipolar grounding fault at DC side;second,the strong bipolar short-circuit current.Theoretical analysis and simulation shows that MMC topology of bridge arm damping module is capable of AC side fault crossing and DC side fault suppression,and can solve the problem above and meet the requirement on VSC-HVDC converter topology of the urban power grid.