Thermal Performances and Annual Damages Comparison of MMC Using Reverse Conducting IGBT and Conventional IGBT Module

Insulated gate bipolar transistor (IGBT) modules in modular multilevel converters (MMCs) have inherent unbalanced power loss distribution and temperature swing. Some chips may become the hotspots and have much larger temperature swing than others, which seriously compromises the lifetime of the IGBT modules. Therefore, effective improvement measures that are low cost become crucial for the IGBT modules in MMC. Reverse conducting IGBT (RC-IGBT) constructs the IGBT and freewheel diode in a single chip, which has the advantages of lower thermal resistance, lower switching loss, and larger heat capacity. In this article, a new generation of RC-IGBT module and conventional IGBT (Con-IGBT) module from Fuji Electric with the same packaging are both used in the MMC. A newly defined current density for RC-IGBT and Con-IGBT module is proposed. The thermal performances and annual damages of the two modules under different power factors are comprehensively compared at the same module current density. The results show that when the power factor is greater than 0.4, using RC-IGBT can significantly improve the thermal performance of MMC submodules (SMs) and extend their lifetime. In addition, the reasons for the comparison results are also discussed in this article. Finally, the advantages of RC-IGBT in terms of thermal performances are verified by experiment. This article also provides a guideline for the design of MMC SMs.