交流侧接地故障对直流配电网电压平衡影响

Impact on the Voltage Balancing of DC Distribution Network Under AC Side Grounding Fault

针对直流配网中换流器交流出口处的单相接地故障,对故障下直流侧正负极电容电压的响应进行了推导,并给出了故障下单个换流站的零序等效电路。对故障消除后直流正负极电压的恢复过程进行了分析。分别从在故障下消除直流正负极电容电压的工频共模波动和在故障消除后直流正负极电压的快速恢复2个角度对电容中点接地电阻的取值进行了讨论。提出了电容中点接地电阻的取值依据。最后通过PSCAD/EMTDC仿真软件进行了直流配网系统故障仿真,对结论进行了验证。

Response of DC capacitor voltage of the voltage source convertor in DC distribution network under asymmetry fault at its internal AC bus is derived. And the zero-sequence equivalent circuit of the converter station under AC side asymmetric fault is obtained. The voltage restoration process of DC side after fault is analyzed. Value of the grounding resistance of DC capacitor midpoint is discussed, based on both the following points, to eliminate the fundamental common-mode oscillations of the DC positive and negative capacitors during fault and to achieve fast recovery of the DC voltage after fault. Value selection rules of the grounding resistance of DC capacitor midpoint are proposed. The conclusion is verified by the results of simulations by PSCAD/EMTDC.