基于边界电流的柔性直流线路保护新方案

基于模块化多电平换流器的柔性直流输电线路保护技术越来越受到关注,由于MMC-HVDC与传统高压直流输电有所差别,提出一种基于边界电流的新型柔性直流线路保护方案。通过对MMC-HVDC直流线路在不同位置发生各类故障时线路边界电流波形的变化特征进行分析,当线路发生内部故障时,其暂态过程中线路整流侧出口电流值明显大于逆变侧出口。当线路发生外部故障时,两端电流值则无明显差异。在此基础上,提出基于边界电流波形差异度的MMC-HVDC直流线路保护判据,并在PSCAD/EMTDC中搭建双端MMC-HVDC模型。大量的仿真结果表明,该保护方案能够正确地判别区内故障和区外故障,具有较高的可靠性。

Protection novel scheme for flexible DC line based on boundary current

More and more attentions are paid to the protection strategy for the MMC-HVDC.Due to the difference between the mmc hvde and traditional HVDC,a new flexible DC line protection scheme is proposed based on the boundary current.Firstly,transient characteristics of both ends of current waveforms are analyzed when various types of faults in HVDC lines occur in different positions.It is noticed that the line current in the rectifier is signifi-cantly greater than that in the inverter side during the transient process of internal fault.Comparably,there are no significant differences between the two ends of current value at external faults.Secondly,a DC line protection strategy for MMC-HVDC is proposed based on boundary current distance.Finally,the simulation and verification of protection strategy are carried out on the 21-level MMC-HVDC system.It is shown that the proposed protection strategy can correctly distinguish the internal fault from the external fault,thus has high reliability.