DC–DC converters are important in medium-voltage direct current (MVDC) distribution networks. For the scenarios where energy flows unidirectionally from MVDC distribution networks to low-voltage direct current (LVDC) loads, the DC–DC converter, which composes of a modular multilevel converter (MMC) on the MVDC side, an uncontrolled rectifier on the LVDC side and a high-frequency transformer as the AC link, is the most cost-efficient candidate. In this study, a new modulation method with quasi-triangular AC-link current is presented to realise zero-voltage turning-on for all switches on the MVDC side, as well as zero-current-switching for the uncontrolled rectifier on the LVDC side. Besides, by adding simple and low-cost voltage-balancing D-L auxiliary circuits between adjacent submodules (SMs), all SM capacitor voltages can be well balanced without voltage sensors. The validity and effectiveness of the proposed method are verified by the simulation and experimental results.

中文翻译：

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单向模块化多电平DC-DC转换器的软开关和无传感器电压平衡调制

DC-DC转换器在中压直流（MVDC）配电网络中很重要。对于能量从MVDC配电网络单向流向低压直流（LVDC）负载的方案，DC-DC转换器由MVDC侧的模块化多电平转换器（MMC）组成，在LVDC侧由不受控制的整流器组成高频变压器作为交流链路是最经济的选择。在这项研究中，提出了一种采用准三角形交流链路电流的新型调制方法，以实现MVDC侧所有开关的零电压导通，以及LVDC侧不受控制的整流器的零电流开关。此外，通过在相邻子模块（SM）之间添加简单且低成本的电压平衡DL辅助电路，没有电压传感器，所有SM电容器的电压都可以很好地平衡。仿真和实验结果验证了该方法的有效性和有效性。