The dc fault-current-limiting technique is extremely important for operation security and power supply reliability of the flexible dc grid. Generally, the dc reactor can effectively limit the dc fault current; however, it will result in negative influences on the system operation stability and dc circuit breaker (DCCB) isolating speed. The hybrid current-limiting circuit (HCLC) can effectively cooperate with the DCCB and avoid the negative influence of dc reactor on the fast fault current clearing, thus being considered as a promising technique in dc grid. In this article, the improved HCLC (I-HCLC) is proposed. It can effectively limit the dc fault current without time delay and eliminate the conduction losses of the used power electronic switches. Compared with the traditional HCLC, the investment of the I-HCLC is significantly reduced for multiport application in multiterminal dc grid. In addition, the improved control strategy, which can avoid the negative influence of dc reactor on the system operation stability, is also researched. Also, this problem has not yet been considered when the HCLC was initially proposed. The experiment tests and simulation cases are carried out to verify the feasibility and superiorities of the proposed I-HCLC and of the improved control strategy.

中文翻译：

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多端柔性直流电网中HCLC的改进拓扑及控制策略


直流故障限流技术对于柔性直流电网的运行安全和供电可靠性极为重要。一般情况下，直流电抗器可以有效限制直流故障电流；然而，这会对系统运行稳定性和直流断路器（DCCB）隔离速度造成负面影响。混合限流电路（HCLC）可以有效地与DCCB配合，避免直流电抗器对快速故障电流清除的负面影响，因此被认为是直流电网中一种有前途的技术。本文提出了改进的HCLC（I-HCLC）。它能有效限制直流故障电流，无延时，并消除所用电力电子开关的导通损耗。与传统的HCLC相比，I-HCLC的投资显着降低，适合多端直流电网的多端口应用。此外，还研究了改进的控制策略，避免直流电抗器对系统运行稳定性的负面影响。而且，HCLC最初提出时还没有考虑到这个问题。通过实验测试和仿真案例验证了所提出的I-HCLC和改进控制策略的可行性和优越性。