基于变基准值比较的MMC电容电压优化均衡控制策略

模块化多电平换流器的子模块电容电压均衡是其稳定运行的关键，传统电容电压均衡策略计算量大，器件平均开关频率高。提出一种基于变基准值比较的电容电压优化均衡控制策略，由最近电平逼近调制计算出当前投入模块的数目，并根据投入模块个数调节基准值，以此基准值为分界点将子模块电容电压序列分为两组，采用随机置乱算法对组内元素排序，根据桥臂电流方向，确定组间排序先后次序，最终确定投入模块信息。同时，通过电容电压优化函数选取合适的电容电压允许偏差阈值及调节因子，实现对器件平均开关频率和电容电压一致性的优化控制；在MATLAB/Simulink中搭建基于MMC的三相逆变器仿真模型，验证所提策略在取得良好均压效果的前提下，降低计算量，同时降低器件平均开关频率。

An Optimized Capacitor Voltage Balancing Control Strategy of Modular Multilevel Converter Based on Comparison of Variable Reference Values

The capacitor voltage balance of modular multilevel converter is the key to its stable operation, aiming at problem of large calculation amount and high switching frequency existing in traditional capacitor voltage balancing strategy. This paper proposes an optimized balancing control strategy of the capacitor voltage based on the comparison of variable reference values. The number of current input modules is calculated by the nearest level modulation, then the reference value is adjusted according to the number of input modules, and based on this reference value, the sub-module capacitor voltage sequences are divided into two groups. At the same time, the random scramble algorithm is used to sort the elements in the group. According to the direction of the bridge arm current, the sequencing order of the groups is determined, and the information of the input module is finally determined. Meanwhile, the permissible deviation threshold of capacitor voltage and the regulatory factor are selected by the optimization function of the capacitor voltage to achieve optimal control of the device's average switching frequency and capacitor voltage consistency. A simulation model of three-phase inverter based on MMC is set up in MATLAB/Simulink to verify the proposed strategy can significantly reduce the amount of calculations and the average switching frequency of the device under the premise of achieving a good effect of capacitor voltage balancing.