双极MMC-HVDC系统直流故障特性研究

直流故障是模块化多电平换流器高压直流输电(MMC-HVDC)的主要故障类型,目前国内外对于MMC-HVDC直流侧故障的研究主要集中于伪双极系统,而对于真双极系统直流侧故障的研究还处于起步阶段。首先,介绍真双极MMC的拓扑结构和工作原理,并根据实际交直流系统电气参数、桥臂子模块电容及电抗的放电机制,建立真、伪双极两种拓扑MMC-HVDC系统直流故障状态下的对应等效电路。然后,对比分析两种拓扑不同阶段故障电流在MMC桥臂上的流通路径,重点研究了故障短路电流对换流站桥臂阀组影响程度的差异,并指出三种电气参数与故障短路电流变化之间的内在关系。最后,基于RT-LAB仿真平台,搭建51电平双极MMCHVDC双端直流输电模型,仿真结果证明了直流故障特性研究方法的正确性。

Study on Characteristics of DC Fault in Bipolar MMC-HVDC System

DC fault is one of the main fault types in modular multilevel converter based HVDC (MMC-HVDC). The current research has mainly focused on pseudo bipolar system, while the research of DC fault in bipolar system is still in the initial stage. Hence, this paper introduces the topology and working principle of MMC in bipolar system. For the bipolar and pseudo bipolar systems, the corresponding equivalent circuits of MMC-HVDC system during DC fault are built respectively according to electrical parameters of AC/DC system, the discharging mechanism of sub-module capacitance and inductor on bridge arms. The effects of fault current on bridge arm valve group in bipolar and pseudo bipolar systems are compared, and the relationship between three electrical parameters and fault current is described. Finally, a 51-level bipolar MMC-HVDC model is set up in RT-LAB. The simulation results validate the method of DC fault characteristics.