用于城轨直流牵引系统的混合型MMC全桥子模块比例设计方法

城市轨道交通直流牵引供电系统是一个低电压大电流系统，受制于开关器件的通流能力，两电平变流器的单台容量难以满足需求。由全桥子模块和半桥子模块组成的混合型模块化多电平换流器（modular multilevel converter, MMC）可用于调制比大于1的系统中，利用全桥子模块的负电平输出能力，可以提高交流电压或降低直流电压。针对可用于城市轨道交通直流牵引供电系统的混合型MMC，提出一种全桥子模块比例的设计方法，满足高调制比稳态运行的需求和直流故障清除能力的需求，选取了常见的1 500 V地铁系统作为算例，选取3组参数，在PSCAD软件中搭建仿真模型，验证了设计方法的正确性。

A Design Method of Hybrid MMC Full-bridge Submodule Proportion Applied to DC Traction Power Supply System for Urban Rail Transit

The characteristic of urban rail DC traction power supply system is low voltage and large current. The capacity of a converter fails to meet the demand, limited by the current capacity of the switching device. Hybrid modular multilevel converter (MMC) is composed of full-bridge submodule and half-bridge submodule. It can be used in systems with modulation ratio greater than one. Utilizing the negative level output capability of the full-bridge submodule, the increase of the AC voltage or the reduction of the DC voltage can be achieved. This article is aimed at the hybrid MMC that can be applied in the DC traction power supply system and proposes a design method for the proportion of full-bridge submodule. This method meets the needs of high modulation ratio steady state operation and DC fault clearing capability. A 1 500 V subway system is selected as an example and three sets of parameters are also selected. The simulation model was built in PSCAD software to verify the correctness of the design method.