不平衡电网下模块化多电平换流器的直流环流均衡策略  

DC Circulating Current Balancing Control of Modular Multilevel Converter under Unbalanced Power Grid

作　　者：潘子迅 杨晓峰[1] 赵锐 崔晨阳 郑琼林[1] Pan Zixun;Yang Xiaofeng;Zhao Rui;Cui Chenyang;Zheng Trillion Q(School of Electrical Engineering,Beijing Jiaotong University,Beijing 100044 China)

机构地区：[1]北京交通大学电气工程学院,北京100044

出　　处：《电工技术学报》2024年第2期541-553,共13页Transactions of China Electrotechnical Society

基　　金：中央高校基本科研业务费专项资金资助项目(2019JBM058)。

摘　　要：不平衡电网下模块化多电平换流器(MMC)存在三相直流环流不均衡问题,易导致相间电流应力和热应力差异,降低其在不平衡工况下安全运行能力。该文从桥臂功率角度分析不平衡电网下三相MMC直流环流不均衡现象和基于零序电压注入的直流环流均衡机理。提出一种零序电压注入的直流环流均衡方法,通过网侧电流与直流环流偏差量计算得到零序电压相位,经过比例谐振控制器生成零序电压注入量,进而实现直流环流的快速、有效均衡。在所提出的控制策略的基础上,研究该方法对MMC桥臂电流峰值、有效值及子模块电容电压纹波的影响规律。仿真与实验结果验证了该文理论分析与控制策略的有效性。Under an unbalanced power grid,the circulating current of a modular multilevel converter(MMC)contains double-line frequency positive,negative and zero sequence components,and unbalanced DC components,leading to unbalanced arm currents.Consequently,asymmetrical electrical stresses and nonuniform temperature distributions exist.However,traditional circulating current control methods generally take the AC components suppression as the control objective and ignore the potential impact of unequal DC components.Therefore,this paper considers unbalanced DC circulating current and proposes a zero-sequence voltage injection method to equalize DC circulating current.In addition,the effects of this method on the arm current and sub-module(SM)capacitor voltage are discussed in detail.Firstly,the DC circulating current equalization mechanism based on zero-sequence voltage injection is analyzed from the arm power transmission perspective.The expression of the amplitude and phase of the zero-sequence voltage is obtained.Then,a zero-sequence voltage injection method is proposed to equalize DC circulating current.The phase of zero-sequence voltage is obtained from the grid current and the deviation of DC circulating current,and a proportional resonant controller is added to adjust its amplitude.After that,the effects of this method on the arm current and SM capacitor voltage are quantitatively studied.The analysis results show that when a single-phase voltage drop occurs,the arm current peak can be reduced by 10.9%at most,and the standard deviation of the arm current root-mean-square(RMS)value can be reduced to zero.Besides,the maximum SM capacitor voltage ripple can drop by more than 8%under the above condition.Simulation and experiment are performed on Matlab/Simulink platform and a three-phase five-level MMC prototype.In the simulation,the proposed method is first applied when single-phase voltage drops to 40%,which shows that the DC circulating current becomes balanced,and both the arm current peak and the maximum SM capacita

关 键 词：不平衡电网 模块化多电平换流器 直流环流 零序电压注入 桥臂电流 子模块电容电压 

分 类 号：TM46[电气工程—电器]