单相接地故障下MMC入网电流耦合机理分析及小信号建模  

Current coupling mechanism and small signal modeling for MMC under single-line to ground fault conditions

作　　者：黄萌[1] 车江龙 查晓明[1] 刘浴霜 盛举 HUANG Meng;CHE Jianglong;ZHA Xiaoming;LIU Yushuang;SHENG Ju(School of Electrical and Automation,Wuhan University,Wuhan 430072,China)

机构地区：[1]武汉大学电气与自动化学院,湖北武汉430072

出　　处：《电力工程技术》2021年第4期52-59,共8页Electric Power Engineering Technology

基　　金：国家自然科学基金资助项目(51637007)。

摘　　要：电网侧发生单相接地故障会造成交流电压一定程度的跌落,此时可通过注入无功电流使模块化多电平换流器(MMC)系统实现故障下的低电压穿越。但接地阻抗会影响整个系统的拓扑结构,使各序网络之间相互耦合,因此对该条件下MMC系统的建模和稳定性进行分析至关重要。文中首先建立单相接地故障下MMC系统交流侧等效模型,并分析混合注入双序无功电流后的故障穿越过程。然后,基于MMC内部子模块电容电压和桥臂电流的动态特性建立MMC系统的小信号模型,并在分析系统失稳机理的基础上,利用根轨迹法分析阻抗参数和电流耦合对MMC系统小信号稳定性的影响。最后,在PSCAD/EMTDC中搭建21电平MMC仿真模型,仿真结果表明,电网阻抗减小或接地阻抗增大使得系统趋于不稳定,负序无功电流注入使得正序无功电流稳定区域增大。Single-line to ground fault occurring on the grid side causes certain drops in alternating current(AC)voltage.At this time,the modular multilevel converter(MMC)system is able to achieve low voltage ride-through under fault with the injection of reactive current.However,the grounding impedance affects the topology of the whole system,thus leading to couplings among the sequence networks.Therefore,modeling and stability analysis of MMC system is of vital significance in this case.The equivalent model of MMC AC system disturbed by single-line to ground fault is established,and the process of fault ride-through with the mixed injection of dual-sequence reactive current is analyzed.Then,based on internal dynamic characteristics of sub-module capacitor voltage and arm current of MMC,the small signal model is established.The influence of impedance parameters and current couplings on small signal stability of MMC are analyzed by using the root-locus method on the basis of system instability mechanism.Finally,a 21-level MMC simulation model is built in PSCAD/EMTDC and the simulation results show that the decrease of the grid impedance or the increase of the ground impedance makes the system tend to be unstable.And the injection of negative sequence reactive current expands the stable region of positive sequence reactive current.

关 键 词：模块化多电平换流器(MMC) 单相接地 序网络 小信号模型 电流耦合 

分 类 号：TM464[电气工程—电器]