基于模块化多电平高压直流输电系统接地故障特性仿真分析

Simulation Research on Earth Fault Characteristics of Modular Multilevel Converter Based High Voltage Direct Current Transmission System

模块化多电平电压源换流器型高压直流输电采用子模块级联结构,解决了开关器件直接串联所带来的动态均压问题,同时具有输出电压波形品质高、开关频率和损耗低等诸多优点,因此成为极具市场应用价值的输电技术之一。在故障时,工作机理、调制策略和拓扑结构的差异导致系统呈现出与传统直流和电压源换流器型直流输电不同故障特性。分别以交流系统侧、阀侧和直流侧接地故障为例,在PSCAD/EMTDC中搭建仿真模型基础上,针对联接变压器绕组不同接线方式,分析其不同故障特性以及对系统运行的影响,并提出了应对策略。

The sub-module cascading structure is applied in the modular multilevel converter based high voltage direct current （MMC-HVDC） transmission system to solve the dynamic voltage balancing brought by directly series-connected switching elements, and the MMC-HVDC transmission system possesses such advantages as high quality of output voltage waveform, lower switching frequency and lower loss and so on, so it becomes one of the power transmission technology that exists high market value. Because the working principle, the modulation strategy and the topological structures of MMC-HVDC transmission system are different from those of traditional HVDC transmission system and voltage source converter based high voltage direct current （VSC-HVDC） transmission system, different fault characteristics appear in MMC-HVDC transmission system under unbalanced grid conditions. Taking the earth fault occurred at the AC system side, the valve side and the DC system side as the cases respectively and considering the influence of connection modes of transformer windings on fault characteristics, based on the simulation model of MMC-HVDC transmission system constructed in PSCAD/EMTDC different fault characteristics under different transformer winding connection modes as well as the influence of above-mentioned three kinds of faults on the operation of MMC-HVDC transmission system are analyzed, and the strategies to cope with these faults are put forward.