六角形模块化多电平AC/AC换流器损耗特性分析计算

Analysis and Calculation of Loss Characteristics for Hexagonal Modular Multilevel AC/AC Converter

详细分析换流器的损耗特性对于系统设计、冷却装置选型都有着重要意义。文中基于全桥子模块的工作特性,对六角形模块化多电平AC/AC换流器(Hexverter)的子模块损耗分布及换流器的总损耗进行分析计算。首先,简要介绍和仿真验证了Hexverter的工作原理。然后,通过提取绝缘栅双极型晶体管(IGBT)模块的数据进行拟合,建立IGBT及其续流二极管的通态特性和开关特性参数,进而对子模块工况进行详细分析,根据全桥子模块的输出特性推导出各器件导通范围及导通时间的解析表达式,从而得到通态损耗和开关损耗的理论计算表达式。最后,通过10 kV系统算例对换流器损耗进行了定量分析,对支路内不同子模块的损耗分布和不同工况下Hexverter的损耗进行计算,结果表明全桥子模块内部的损耗分布呈现对称性外,同一支路内各子模块损耗也不尽相同,特别是在不同容量及功率因数的工况下,子模块损耗分布及换流器总损耗存在明显差异。

The detailed analysis of loss characteristics for converter is of great importance for system design and cooling device selection. This paper analyzes and calculates the loss distribution of submodule and the total loss of converter based on the working characteristics of full bridge submodules in hexagonal modular multilevel AC/AC converter(Hexverter). Firstly, the operation principle of Hexverter is briefly introduced and simulated. Secondly, the on-state and switching characteristics of insulated gate bipolar translator(IGBT)and freewheel diode are established by fitting the data of IGBT module. The working conditions of submodule are analyzed in detail. According to the output characteristics of full bridge submodule, the analytical expressions of conduction range and the time of each device are derived, respectively. Then the theoretical analysis expressions of conduction loss and switching loss are obtained. Finally, the loss of the converter is quantificationally analyzed in 10 kV system, the loss distribution of different submodules is calculated, and the losses of Hexverter in different working conditions are calculated. The results show that the loss distribution in full bridge submodule is symmetrical, and the loss of each submodule in one branch is not the same. Additionally, the loss distribution of submodules and the total loss of the converter are obviously different, especially in various working conditions of different capacities and power factors.