直流断线故障特性分析及一种基于控制的保护策略

Analysis on Characteristic of DC Network Line Breakage Fault and a Control-based Protection Strategy

随着“直流电网”概念的形成,传输距离的增长使得架空线成了构建直流传输网络的最佳选择。相较电缆线路,架空线故障率更高,更易发生断线故障。基于多端柔性直流环网拓扑结构,对直流网络中部分线路断开后换流站及相连线路的暂态特性进行了研究,阐述了故障后产生直流侧过电压以及非故障线路过电流的机理;以抑线路过电流水平、加快系统恢复速度为目的,提出改进后的电流控制器模型。最后,基于PSCAD/EMTDC搭建了四端环网模型,验证了提出的控制策略的有效性,能够明显的抑制线路过流峰值和加快直流网络恢复速度。

With the expansion of the scale of“DC power grid”and the increase of transmission distance,overhead line has become the best choice to construct DC transmission network.Compared with cable lines,overhead lines have higher failure rate and are more prone to break down.Based on the topology of flexible DC loop network,the transient characteristics of converter stations and connected lines after disconnection fault are studied in this paper.The mechanism of DC side overvoltage and non-fault line overcurrent after fault is described.In order to suppress the transient components and speed up the system recovery,an improved current controller model is proposed.Finally,a four-terminal loop network model based on PSCAD/EMTDC is built to verify the effectiveness of the proposed control strategy,which can significantly suppress the peak overcurrent and improve the transient characteristics of converter station during fault.