This article proposed a single-phase active neutral point clamped seven-level (SANPC-7L) inverter topology with only eight power switches and three dc-link capacitors. Compared with the existing single-phase seven-level inverters, the quantity of power switches and voltage stresses across them are both reduced. Modulation logic expression of every switch is derived based on the Karnaugh map technique. Like the existing counterparts with three series-connected dc-link capacitors, there is a severe capacitor voltage imbalance issue. This issue is hard to address as there are no redundant switching states that can be selected to balance the dc-link capacitor voltages. This article gives a comprehensive analysis on the capacitor voltage imbalance issue. It indicates that the over charge or discharge of the middle capacitor voltage is the root cause of this issue, while the upper and lower capacitor voltages can be automatically balanced. To overcome this issue, a variable-reference voltage-balance control method is used to enable a three-level voltage waveform to appear in every switching period, and thus the middle capacitor voltage can be controlled at 1/3 of the dc-link voltage. Both the simulation and experimental results have been presented to verify the proposed topology with the variable-reference voltage-balance control strategy.

中文翻译：

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单相有源中性点钳位七电平逆变器的拓扑结构和电压平衡控制

本文提出了一种单相有源中性点钳位七电平 (SANPC-7L) 逆变器拓扑结构，只有八个电源开关和三个直流链路电容器。与现有的单相七电平逆变器相比，电源开关数量和电压应力都减少了。每个开关的调制逻辑表达式是基于卡诺图技术推导出来的。与具有三个串联直流链路电容器的现有同类产品一样，存在严重的电容器电压不平衡问题。这个问题很难解决，因为没有可以选择的冗余开关状态来平衡直流链路电容器电压。本文对电容器电压不平衡问题进行了综合分析。说明中间电容电压过充或过放电是造成此问题的根本原因，而电容上下电压可自动平衡。为了克服这个问题，采用可变参考电压平衡控制方法，使每个开关周期都出现三电平电压波形，从而可以将中间电容电压控制在直流母线电压的1/3 . 仿真和实验结果都被提出来验证所提出的具有可变参考电压平衡控制策略的拓扑结构。因此中间电容器电压可以控制在直流母线电压的 1/3。仿真和实验结果都被提出来验证所提出的具有可变参考电压平衡控制策略的拓扑结构。因此中间电容器电压可以控制在直流母线电压的 1/3。仿真和实验结果都被提出来验证所提出的具有可变参考电压平衡控制策略的拓扑结构。