模块化多电平变流器的子模块分组调制及均压控制

The Grouping Modulation and Voltage Balance Control of the Sub-modules in Modular Multilevel Converter

模块化多电平变流器很容易扩展到更高电压等级的应用场合,但是当子模块数目很多时,桥臂中电容电压的均衡和触发脉冲的分配就变得很复杂,控制系统也因此变得复杂,降低了可靠性,增加了调试的难度。在研究最近电平逼近调制(nearest level modulation,NLM)算法的基础上,提出取整修正量移位算法,不同的子模块组采用不同的取整修正量,可以达到类似于载波移相的效果,使桥臂输出电压的畸变很小。分析子模块组电容均压原理,提出两种均压控制方法,并给出这两种方法的适用条件。取整修正量移位算法相当于在调制波中增加了直流分量,可以通过排序算法,控制子模块组之间的电压均衡。仿真结果显示,取整修正量移位算法和均压控制算法能够达到预期效果。

Modular Multilevel Converter（MMC） can be easily applied to higher voltage and large-scale capacity situations. But when the number of sub-modules is large enough, the capacitor voltage balance and gating pulse distribution in the arm become much more complex, leading to the increased complexity of the control system, the reduced reliability, and much harder debugging. In this paper, the Nearest Level Modulation（NLM） algorithm was introduced in detail, and on this basis, the Floor Modify Number Shifting（FMNS） algorithm was proposed. Since different sub-module groups adopt different floor modify numbers, the effect of carriage phase shift can be achieved, and the distortion of the output voltage is very small. Furthermore, the capacitor voltage balance principle of the sub-module group was analyzed, two capacitor voltage balance control methods were proposed based on this principle, and the application conditions were analyzed in detail. Simulation results show that the prospective effect can be achieved through FMNS algorithm and voltage balance control algorithm.