常规变换器变频运行控制方法缺乏对变换器各模块之间功率差的定量分析，导致变换器变频运行控制开关频率较高，为此提出基于PLC的模块化多电平变换器变频运行控制研究。根据电压调制原理，将三角载波分为两个模块，用于调整变换器的电压，结合低频工况子模块调整后的电压，计算多电平变换器变频运行误差；根据运行误差定量分析变换器各模块之间的功率差以及PLC技术，构建模块化多电平变换器变频运行控制模型，从而控制变换器变频运行。实验结果表明，所设计模块化多电平变换器变频运行控制方法下的开关频率低至251 Hz，该方法能够优化开关频率的波动。

The conventional inverter frequency conversion operation control method lacks quantitative analysis of the power difference between various modules of the converter, resulting in a high switching frequency for inverter frequency operation control. Therefore, a PLC-based study on modular multilevel inverter frequency conversion operation control is proposed. According to the principle of voltage modulation, the triangular carrier wave is divided into two modules, which are used to adjust the voltage of the converter. Combined with the adjusted voltage of the low - frequency operating submodule, the frequency conversion operation error of the multilevel converter is calculated. Based on the quantitative analysis of the power difference between various modules of the converter and PLC technology, a modular multilevel converter variable frequency operation control model is constructed to control the variable frequency operation of the converter. The experimental results show that the switching frequency is as low as 251 Hz under the variable frequency operation control method of modular multilevel converter, and this method can optimize the fluctuation of switching frequency.