不对称双极多端柔性直流电网短路电流特性分析

含金属回线的不对称双极柔性直流电网的短路电流特性分析是其故障类型判别和故障隔离的基础。不对称双极电网发生各种故障时的短路电流具有相似的特性,难以区分。文中针对不对称双极多端直流电网的短路电流特性进行分析。首先,建立直流电网的等效电路,其中换流器和线路分别简化为RLC串联电路和RL串联电路;然后,基于建立的等效电路,分析了单端换流站的短路电流特性;最后,基于单端换流站短路电流特性,分析各换流站的放电回路,研究了不对称双极多端柔性直流电网在各种故障类型下的短路电流特性。中国张北双极柔性直流电网的仿真结果验证了分析得到的多端柔性直流电网短路电流特性的正确性。

Characteristic Analysis on Short-circuit Current for Asymmetric Bipolar Modular Multilevel Converter Based Multi-terminal Direct Current Grid

Characteristic analysis on short-circuit current for asymmetric bipolar modular multilevel converter (MMC) based multi-terminal direct current (MMC-MTDC) grid with dedicated metallic return (DMR) is the foundation of its fault type discrimination and fault isolation. The characteristics of short-circuit currents with different faults are similar, which are difficult to distinguish. This paper analyzes the short-circuit current characteristics of asymmetric bipolar MTDC grids. Firstly, the equivalent circuit of the MTDC grid is established, where the converter and overhead line are simplified to RLC series circuit and RL series circuit, respectively. Then, based on this, the short-circuit current characteristics of a single-terminal converter station are analyzed. Finally, based on the short-circuit current characteristics of a single-terminal converter station, the short-circuit current characteristics of the asymmetric bipolar MMC-MTDC grid with various faults are studied by analyzing the discharging circuit of MMCs. Simulation results on the Zhangbei bipolar MMC-MTDC grid of China validate the correctness of the characteristic analysis on short-circuit current for MMC-MTDC grids.