一种提高MMC交流电压鲁棒性的改进调制策略

An Improved Modulation Strategy for Improving the Robustness of MMC AC Voltage

柔性直流输电技术被认为是目前应用于新能源大规模接入的较好解决方案,且可接入弱交流系统。柔性直流输电工程大多基于模块化多电平换流器（modular multilevel converter,MMC）,工程中MMC采用最近电平逼近调制（nearest level modulation,NLM）策略。在系统发生扰动或故障使得直流电压波动时,采用传统NLM调制策略的MMC换流器输出的交流电压稳定性较差。该文分析了传统NLM调制策略存在以上缺陷的原因,并针对该原因,提出了一种考虑子模块电容电压实际值的改进调制策略,从而使MMC输出的交流电压在系统扰动时具有较好的鲁棒性。通过在PSCAD/EMTDC中搭建电磁暂态模型并进行仿真分析,验证了该文提出的改进调制策略可以有效提升MMC换流器输出交流电压的鲁棒性。

Flexible HVDC technology is considered an advantageous solution applied to large-scale wind power integration.Flexible HVDC are mostly based on modular multilevel converter（MMC）,generally adopting nearest level modulation（NLM） strategy.If the MMC adopts traditional NLM strategy,then when a disturbance or fault occurs in the system,causing DC voltage fluctuates,the output AC voltage of MMC will have poor stability,unable to meet demand for wind farm integration.This paper analyzes the reason of above defects of traditional NLM strategy,and proposes an improved modulation strategy.The strategy considers actual value of capacitor voltage,so that the output AC voltage of MMC has good robustness.By building an electromagnetic transient model in PSCAD/EMTDC and carrying out simulation analysis,this paper verifies that the improved modulation strategy can effectively enhance AC voltage robustness of MMC.