Medium-voltage connected ultra-fast chargers are getting more popular for charging electric vehicles with large battery capacities. Here, the solution based on a modular multilevel converter is more promising, since the isolation stage can be realized as a single medium-frequency transformer interconnecting the modular multilevel converter to a single-phase ac/dc converter. A new operating scheme is proposed for this converter, enabling zero-voltage switching and nearly zero-current switching across the entire load range. In contrast to the conventional phase-shift control method, the proposed scheme effectively reduces the reactive power through the ac/dc converter, leading to decreased turn-off switching losses in the ac/dc converter and a lower RMS current stress in the power path. A control scheme, integrating the operating principle, is developed for the modular multilevel converter. The method is verified through simulation and measurements on a scaled-down prototype. The results validate the theoretical analysis and practical feasibility of the proposed operating principle and the developed control scheme.

中文翻译：

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MMC-Fed AC/DC 转换器的开关损耗降低

中压连接超快速充电器在为大电池容量的电动汽车充电时越来越受欢迎。在这里，基于模块化多电平转换器的解决方案更有前途，因为隔离级可以实现为将模块化多电平转换器互连到单相交流/直流转换器的单个中频变压器。为该转换器提出了一种新的操作方案，可在整个负载范围内实现零电压开关和接近零电流的开关。与传统的相移控制方法相比，该方案有效地降低了交流/直流转换器的无功功率，从而降低了交流/直流转换器的关断开关损耗，并降低了功率路径中的RMS电流应力。结合工作原理，为模块化多电平变换器开发了一种控制方案。该方法通过在按比例缩小的原型上进行仿真和测量进行了验证。结果验证了所提出的工作原理和所开发的控制方案的理论分析和实际可行性。