不平衡电网电压条件下MMC控制策略综述

Review of Control Strategies for Modular Multilevel Converter under Unbalanced Grid Voltage

模块化多电平换流器MMC(modular multilevel converter)中负序电流的有效抑制对提高电能传输质量和系统稳定性具有重要意义。随着电网中出现不平衡故障的概率与日俱增,平衡网压下MMC的控制策略已不再适用。为此,从MMC内、外特性的影响因素出发,对国内外的研究现状进行归纳总结,并基于现有研究展望未来。首先,从外特性角度分析三个控制目标下不同控制策略的异同点,再进一步阐述引入多变量控制参数k后各电气量的变化趋势,并指出这些方法存在的局限性;其次,从内特性角度梳理环流注入、三次谐波注入对桥臂电流、电容电压的影响,并对相关研究的共性问题进行分析;最后,综合国内外对相关问题的分析与思考,提出该领域目前所面临的挑战,对未来需要深入探究的方向做出了展望。

The effective suppression of negative-sequence current in a modular multilevel converter(MMC) is of significance to improving the power transmission quality and system stability.With the increasing probability of unbalanced faults in power grid,the control strategies for MMC under balanced grid voltage are no longer applicable.Therefore,starting from the influencing factors of internal and external characteristics of MMC,the research status both at home and abroad is summarized,and the future based on the existing research is forecasted.First,the similarities and differences of different control strategies under three control objectives are analyzed based on the external characteristics,the varying trend of each electrical quantity after the introduction of multi-variable control parameter k is further explained,and the limitations of these methods are pointed out.Second,based on the internal characteristics,the effects of circulation injection and third harmonic injection on the bridge arm current and capacitor voltage are sorted out,and the common problems of related research are analyzed.Finally,through the comprehensive analysis and consideration of related issues both at home and abroad,the existing challenges in this field are put forward,and the prospect for the future direction that needs in-depth exploration is forecasted.