一种新型模块化多电平换流器子模块拓扑

模块化多电平换流器（MMC）采用模块化设计，通过调整子模块的串联个数可以实现电压及功率等级的灵活变化，其普遍子模块（半桥、全桥结构子模块）的输出为0、1两种电平。提出了一种新型模块化多电平换流器子模块拓扑结构并介绍了其工作原理。该种子模块可以输出0、1、2三种电平，与原有的半桥结构相比，在输出同样电平数的情况下，该新型拓扑可以节省25％的IGBT，减少了子模块的总数和换流站的占地面积。成功地将最近电平逼近调制（nearest level modulation，NLM）策略应用到新型拓扑上，并给出了相应的电容电压控制策略。在PSCAD仿真环境中搭建基于NLM的11电平两端MMC—HVDC输电系统，仿真结果表明子模块电容、直流电压和谐波均满足要求，验证了所提拓扑和控制策略的正确性与有效性。

A New Scheme of Sub-Module Topology for Modular Multi-level Converter

Modular multi-level inverter (MMC) is modular in design, and able to realize flexible changes in the levels of voltage and power with adjusting the number of sub-module series, and its universal sub-module such as half-bridge, full-bridge structure sub-module has two voltage levels of 0 and 1 to output. This paper proposes a new scheme of sub-module topology for modular multi-level converter, and explains correlative operation principle. The sub-module in the new scheme can output three voltage levels of 0, 1 and 2, and thus in comparison with the original half-bridge structure, for the same output level number, the new topology can save up to 25% of the IGBT, and reduce the total number of sub-modules and the footprint of the converter station. Proposing the corresponding capacitor voltage modulation strategy, the paper does a successful application of the nearest level modulation strategy to the new topology, An NLM based Double-end 11 levels of MMC-HVDC transmission system is set up in the PSCAD simulation environment, and its simulation results show that sub-module capacitor, DC voltage and harmonic are all in agreement with the re-quirements, verifying the correctness and validity of the proposed topology and control strategy.