基于损耗分析的全桥型MMC参数优化设计

全桥型模块化多电平换流器(MMC)具有直流故障自清除能力,且在发生故障时能够支撑交流侧电压,特别适用于架空线传输的柔性直流输电系统。但是其损耗大的问题十分突出,制约了其在大功率场合的应用。传统设计方法认为在全桥型MMC正常运行时负电平是无效电平,故而提出一种基于模块输出负电平特性的效率优化设计方法。分析子模块输出负电平时全桥型MMC中各电气量满足的约束关系,推导效率最优的直流电压、交流侧电压以及桥臂子模块数的表达式。该方法能在系统额定功率和开关器件型号确定的条件下,准确求解效率最优的MMC系统设计参数。

Optimization design of full bridge MMC parameters based on loss analysis

The full bridge MMC(Modular Multilevel Converter) is suitable for the overhead line transmission of VSC-HVDC(Voltage Source Converter based High Voltage Direct Current),due to its capabilities of riding through DC short circuit fault and supporting AC voltage. However, the huge power loss of full bridge MMC imposes a great challenge on its applications in high power occasions. The negative levels of full bridge sub-modules are not utilized during normal operations in the traditional design of full bridge MMC. Hence, an efficient optimization design approach based on the negative levels of full bridge MMC is proposed. The constraints that the power variables of the full bridge MMC should satisfy are analyzed. Then, the optimal DC voltage, AC voltage and sub-module number are derived. The proposed approach can accurately provide the optimal design parameter of MMC system under the rated power and the certain switching devices.