This paper proposes a novel multilevel topology “Modular-Isolated-Multilevel-Converter” which achieves almost zero low frequency capacitor voltage fluctuation. It inherits the structure of MMC but replaces the half bridge module by the newly proposed Isolated Half-Bridge (IHB). The fundamental and 2^nd order harmonic frequency current originally in the MMC module capacitor have been eliminated through connecting the secondary sides of the IHB at the same level of the three phases together. The elimination is due to that the 1^st and 2^nd order components in the arm current are 120° phase shifted in three phases. Therefore, the module capacitance is reduced by more than 10 times since it only carries switching frequency ripple. Moreover, the arm inductance can also be significantly reduced since the 2^nd order harmonic current disappears. The topology is specifically suitable for variable frequency drive application, because its capacitance and inductance are not affected by the output frequency. The challenges of zero frequency start-up when MMC is adopted for VSD can be addressed here. In the paper, the operation principle of the proposed MIMC is fully analyzed and the mathematical model is built. Moreover, a methodology of capacitor sizing and arm inductor design for general MMC topology is proposed. The detailed design considerations for MIMC are also discussed and presented. The plant modeling and control strategy have been proposed for MIMC. A 55-kW simulation is carried out to verify the theoretical analysis. And a 6-kW downscaled hardware prototype is also developed to demonstrate the benefits of the new topology over the traditional MMC.

中文翻译：

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一种基于隔离CLLC谐振电路的具有纹波电流消除通道的新型模块化多电平转换器

本文提出了一种新颖的多电平拓扑“模块化隔离多电平转换器”，可实现几乎为零的低频电容器电压波动。它继承了MMC的结构，但用新提出的隔离半桥（IHB）取代了半桥模块。通过将三相同级IHB的次级侧连接在一起，消除了MMC模块电容器中原有的基波和二次^{谐波频率电流。}淘汰是因为^第一和^第二臂电流中的阶分量在三相中相移 120°。因此，模块电容减少了10倍以上，因为它只承载开关频率纹波。^{此外，自 2 nd}以来，臂电感也可以显着降低次谐波电流消失。该拓扑特别适用于变频驱动应用，因为其电容和电感不受输出频率的影响。当 MMC 用于 VSD 时，零频率启动的挑战可以在这里解决。本文对所提出的 MIMC 的工作原理进行了全面分析，并建立了数学模型。此外，还提出了一种用于通用 MMC 拓扑的电容器尺寸和臂电感设计方法。还讨论和介绍了 MIMC 的详细设计注意事项。已为 MIMC 提出了工厂建模和控制策略。进行了 55 kW 的模拟以验证理论分析。并且还开发了一个 6 kW 缩小的硬件原型，以展示新拓扑相对于传统 MMC 的优势。