MMC子模块电容电压波动及谐波研究  

Capacitor Voltage Ripple and Harmonics Analysis in MMC

作　　者：邹凯凯 李钢[1] 邹强[1] 董云龙[1] 卢宇[1] ZOU Kaikai;LI Gang;ZOU Qiang;DONG Yunlong;LU Yu(Nanjing Nanrui Jibao Electric Co.,Ltd.,Nanjing 211100,Jiangsu,China)

机构地区：[1]南京南瑞继保电气有限公司,江苏南京211100

出　　处：《南方能源建设》2023年第5期129-138,共10页Southern Energy Construction

基　　金：国家电网有限公司总部管理科技项目资助“新能源经柔性直流送出系统在多类型谐波扰动下的穿越能力及控制策略研究”(5100-202256371A-2-0-ZN)。

摘　　要：[目的]柔性直流的快速发展为MMC(Modular Multi-Level Converter,模块化多电平变流器)拓扑确定了实践支撑。文章以半桥MMC换流器为例,研究MMC稳态电容电压波动、谐波交互规律及桥臂开关函数的关系,以对MMC系统设计、控制策略给予理论支持。[方法]通过建立子模块电容电压、桥臂开关函数的解析表达式,得到MMC换流器上下桥臂能量波动及电容电压波动的数学近似表达式,进而研究了上下桥臂电流、交流阀侧、直流侧中各次谐波的分布规律及相间环流的正负序关系,基于谐波公式得到二次环流的估算方法;进一步,采用变量对照法研究了桥臂开关函数、子模块电容电压随阀侧功率因数、子模块电容大小的变化关系;最后基于实际工程参数搭建了详细的PSCAD/EMTDC模型,开展了理论解析与离线仿真的一致性对比。[结果]研究表明:MMC相间环流只含偶数次谐波,且其中6k+2次环流呈负序、6k+4次环流呈正序、6k次环流呈零序特性,同时稳态下MMC阀侧出口交流电压电流只含奇数次谐波,MMC直流侧电压电流只含偶数次谐波,且在功率因数角φ<0的某些范围内桥臂开关函数峰值会大于1,在低功率因数下子模块电容电压波动峰值大于高功率因数下的波动。[结论]可由此开展换流器电容容值的选型设计及暂稳态策略研究,并通过理论解析掌握MMC拓扑的运行本征特性。[Introduction]The rapid development of VSC-HVDC provides practical support for MMC(Modular Multi-Level Converter)topology.Takes a half bridge MMC converter as an example,the relationship between steady-state capacitor voltage fluctuation,harmonic interaction,and bridge arm switching function of MMC is studied in order to provide theoretical support for MMC system design and control strategy.[Method]By establishing analytical expressions for the sub module capacitor voltage and bridge arm switch function,the mathematical approximate expressions for the energy fluctuation and capacitor voltage fluctuation of the upper and lower bridge arms of the MMC converter were obtained.Furthermore,the distribution law of harmonics in the upper and lower bridge arms current,AC(Alternating Current)valve side,and DC(Direct Current)side,as well as the positive and negative sequence relationship of inter phase circulation were studied.Based on the harmonic formula,an estimation method for the secondary circulation was obtained;Furthermore,the variable comparison method was used to study the relationship between the switching function of the bridge arm and the voltage of the submodule capacitance with the valve side power factor and the size of the submodule capacitance.Finally,a detailed PSCAD/EMTDC model was built based on actual engineering parameters,and a consistency comparison between theoretical analysis and offline simulation was conducted.[Result]The research has shown that the inter phase circulating current of MMC only contains even harmonics,with 6k+2 circulating currents exhibiting negative sequence,6k+4 circulating currents exhibiting positive sequence,and 6k circulating currents exhibiting zero sequence characteristics.At the same time,under steady-state conditions,the AC voltage and current flow at the outlet of MMC valve side only contains odd harmonics,while the DC voltage and current flow at MMC DC side only contains even harmonics,and at the power factor angleφ<0,the peak value of the bridge arm switch function

关 键 词：MMC 子模块电容电压波动 桥臂开关函数 谐波电压 谐波电流 

分 类 号：TM7[电气工程—电力系统及自动化] TM712