摘要
全/半桥子模块混合型模块化多电平换流器(modular multilevel converter,MMC)由于具备直流故障穿越能力并兼顾了制造成本,成为当下柔性直流输电领域的研究热点之一。全桥子模块具备负电平输出能力,混合型MMC可以提升电压调制比,运行在过调制状态,提升运行效率。但是混合型MMC在过调制运行工况下的电流、热应力分布特性尚不明晰,为此针对混合型MMC在过调制下的全/半桥子模块开关器件的电流应力及热应力展开研究。通过分析混合型MMC在过调制下的工作原理和特性,结合仿真着重研究了不同电压调制比以及不同功率因数下换流器的损耗分布特性;归纳出了直流电流调制比的概念。研究发现随着直流电流调制比的增大,子模块内部开关器件的损耗—热应力分布不均程度加大,危及MMC安全运行,结论可以为混合型MMC的设计和优化提供指导。
Hybrid modular multilevel converter(Hybrid-MMC) using both half-bridge sub-modules(HBSM) and full-bridge sub-modules(FBSM) in arms can ride through DC fault and reduce the switches compared with FBSM-MMC, which is considered as a promising topology in Voltage Source Converter based High Voltage Direct Current(VSC-HVDC). Additionally, the voltage modulation ratio m can be promoted by utilizing the negative arm voltage output so that the power transmission and efficiency can be enhanced. However, under over-modulation operation(m>1), the current and thermal distribution in HBSM and FBSM become different from that of traditional modulation(m<1) due to the more complex modulation mode and operation principle. So in this paper, based on the analysis of the characteristics of hybrid MMC under over-modulation operation, the current stress and power loss under different modulation index and different power factor operation is emphasized in research with simulation. The concept of current modulation ratio is generalized finally and based on the concept the conclusion is made that the power loss in SMs' switching devices becomes more imbalanced with the increase of current modulation ratio.
出处
《全球能源互联网》
2018年第4期445-453,共9页
Journal of Global Energy Interconnection
基金
国家重点基础研究发展计划(973)青年科学家专题(2014CB247400)
国家自然科学基金项目(51490682)~~
