模块化多电平变换器的系统状态方程及等效模型

The System State Equation and Equivalent Model of Modular Multilevel Converters

模块化多电平变换器(modular multilevel converter,MMC)由于其模块及变量数量众多,造成其仿真及分析的困难。在忽略系统高频分量及假定模块电容电压均等的前提下,引入正负桥臂电容电压之和及差作为新的变量,并和环流及输出电流一起建立了系统的状态方程。以该方程为基础,提出了系统的一种等效模型。该模型以简单的电容和逆变器模型为基础,从而使得系统分析变得十分直观和简单。为提高模型的精确性,该文分析了死区及IGBT饱和压降对系统的影响,给出了修改后的等效模型及其s域模型,该模型可以替换实际的MMC系统用于仿真研究,而不必考虑仿真速度的问题。最后,通过仿真和实验证实了所提模型的正确性。

Applications of the modular multilevel converter （MMC） in the mid- and high voltage places have received extensive attention, but the numerous sub-modules bring difficulties for the analysis. In this paper, assuming the system is continuous and ideal, the system state equations of single phase are deduced about the four variables as the circulating current, the load current, the sum and the difference of the capacitor voltages between the positive and the negative legs in a phase. Based on the system state equations, the system equivalent model is established, which makes the physical relationship among the variables of the system become very clear. And then, effects of the dead time and the IGBT saturation voltage drop on the system are analyzed to improve the equivalent model, and the corresponding s-domain model is presented that can be used for simulation study of the MMC. Finally, simulation and experimental results confirm the accuracy of the proposed model.