柔性直流电网故障电流复合抑制策略

柔性直流电网在直流侧发生短路故障后，故障电流迅速达到较大峰值，严重时会危及整个系统电气设备的安全运行。为了在故障发生后的短时间内限制故障电流影响，提出一种不利用附加装置的电流抑制策略。首先，分析了直流电网结构与故障初期电流上升规律。然后，根据所得规律提出一种包含两个环节的电流复合抑制策略，给出电流抑制参数选取的原则，并分析了抑制策略下短路电流的发展规律。最后，在PSCAD/EMTDC平台搭建四端柔性直流电网模型进行仿真验证。结果表明，所提电流抑制策略可以有效减小直流线路过流倍数，降低换流器闭锁的概率，且故障切除后恢复阶段电流平衡度更好。

Composite fault-current suppression strategy for flexible DC grids

After a short-circuit fault occurs on the DC side of a flexible DC grid, the fault current quickly reaches a large peak, which can endanger the safe operation of the electrical equipment throughout the system. To limit the influence of fault currents within a short period after the fault, a current-suppression strategy without using additional devices is proposed. First, the structure of the DC grid and the law of rising of the current during the initial fault stage are analyzed. Then, based on the obtained law, a composite current suppression strategy including two links is proposed, the principle of selecting current-suppression parameters is given, and the development law of short-circuit current with the suppression strategy is analyzed. Finally, a four-terminal flexible DC grid model is built on the PSCAD/EMTDC platform for simulation verification. The results show that the proposed current suppression strategy can effectively decrease the overcurrent multiple of the DC line, reduce the probability of converter blocking, and achieve better current balance in the recovery phase after fault removal.