电网电压平衡下模块化多电平换流器的环流稳态分析

Steady State Analysis of Modular Multilevel Converter under Grid Voltage Balanced

模块化多电平换流器(Modular Multilevel Converter,MMC)内部环流的存在增大了桥臂电流的有效值和峰值,增加了子模块电容电压的波动幅度,影响电力电子器件的安全运行,因此,有必要对MMC内部环流特性进行分析.通过子模块电容电压变化的研究,从时域的角度建立描述环流特征的二阶微分方程.在稳态情况下通过近似处理方法求得微分方程的特解并忽略微分方程的通解,该特解主要是由直流分量和二次分量构成,可以有效地描述电网电压平衡下的环流稳态特性,并在PSCAD中搭建了5电平的MMC模型,仿真结果验证了理论分析的有效性与正确性.

Modular multilevel converter internal circulating current increases the peak ann current and RMS, increases the fluctuation of sub module capacitor voltage and affects the safe operation of power electronic de- vices, therefore, It is necessary to analyze the circulating current. In this paper, the two order differential equa- tion describing the circulation characteristics is established from the viewpoint of time domain. The approximate method to obtain differential equations special solution and ignore the general solution of differential equation in the steady state,the solution is mainly composed of the DC component and the two component,which can ef- fectively describe the characteristics of steady state circulation under the balance of power grid voltage, and set up the MMC model of 5 level in PSCAD. The simulation results verify the validity and correc-ness of the theo- retical analysis.