Two novel floating capacitor voltage balancing schemes are proposed in this article, which enhance the linear modulation range of single-source seven-level inverters having floating capacitor fed H-bridge units. Extreme pole voltage levels associated with cascaded H-bridge units can be used for enhancing dc bus utilization. But, these pole voltage levels lack redundant switching states, which limits the linear modulation range for which floating capacitor voltages remain balanced. In recent times, a few literature have addressed the issue of balancing these capacitor voltages by employing appropriate modulation schemes, which enhances the modulation range of a inverter to a certain extent. The proposed balancing schemes further extend the linear modulation range by adding a suitable common-mode offset to reference signals. The addition of a predefined low-frequency offset and an online calculated dynamic offset is proposed here that helps in extending the modulation ranges to 0.84 and 0.85. Under these schemes, the dc bus utilization can reach up to 0.637Vdc at unity power factor, where Vdc is the input voltage of the single-source inverters. Three well-established optimized seven-level inverters are used to analyze these schemes and their effectiveness is demonstrated using simulation and experimental results at different modulation and load conditions.

中文翻译：

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具有电容馈电 H 桥单元的单源七电平逆变器的增强型浮置电容电压平衡方案


本文提出了两种新颖的浮动电容器电压平衡方案，该方案增强了具有浮动电容器馈电H桥单元的单源七电平逆变器的线性调制范围。与级联 H 桥单元相关的极端极电压水平可用于提高直流母线利用率。但是，这些极电压电平缺乏冗余开关状态，这限制了浮动电容器电压保持平衡的线性调制范围。近年来，一些文献通过采用适当的调制方案解决了平衡这些电容器电压的问题，这在一定程度上提高了逆变器的调制范围。所提出的平衡方案通过向参考信号添加合适的共模偏移来进一步扩展线性调制范围。这里建议添加预定义的低频偏移和在线计算的动态偏移，这有助于将调制范围扩展到 0.84 和 0.85。在这些方案下，直流母线利用率在单位功率因数下可达 0.637Vdc，其中 Vdc 是单源逆变器的输入电压。使用三个完善的优化七电平逆变器来分析这些方案，并使用不同调制和负载条件下的仿真和实验结果证明其有效性。