基于MMC的多端直流电网通用计算方法及拓扑优化研究

针对现有直流电网直流侧短路简化计算方法普遍不适用于对称单极接线系统及短路故障后故障电流急剧上升导致换流站闭锁的问题，提出了适用于对称单、双极接线方式直流电网的通用计算方法和直流电网拓扑优化方法。首先，分析了不同接线方式下的直流电网直流侧单、双极短路故障特性。其次，基于阻抗频率特性提出了适用于不同接线方式直流电网的故障电流计算方法，并得到了评价故障电流水平的简化指标，有效地评估直流电网拓扑变化时的故障电流水平，实现多端系统的拓扑优化，降低单极接地故障电流水平。最后，通过电磁暂态仿真案例验证了所提计算方法和简化指标的准确性和有效性。

MMC-based General Calculation Method and Topology Optimization of DC Power Grid

The existing simplified calculation method of DC side short circuit in DC power grid is generally not applicable to symmetrical unipolar system， the rapid rise of fault current after short circuit fault leads to the blocking of converter station. A general calculation method and DC power grid topology optimization method suitable for symmetrical unipolar and bipolar connection DC power grid are proposed. Firstly，the characteristics of DC side pole-to-ground and pole-to-pole short circuit fault in different connection modes are analyzed. Secondly， a fault current calculation method suitable for DC power networks with different connection modes is proposed based on the impedance frequency characteristics，and a simplified index to evaluate the fault current level is obtained. This index can effectively evaluate the fault current level when the DC grid topology changes， thus realizing the topology optimization of the multi-terminal system and reducing the pole-to-ground fault current level. Finally， the accuracy and effectiveness of the proposed calculation method and simplified index is verified by electromagnetic transient simulation software.