Analysis of IGBT Junction Temperature Fluctuation in Modular Multilevel Matrix Converter

The modular multi-level matrix converter (M3C) is a crucial component of the flexible low-frequency transmission system. However, during AC-AC frequency conversion, the power of the AC system on both sides, with different frequencies, is directly coupled in the inverter. The converter bridge arm is subjected to two different frequencies of AC currents simultaneously, resulting in irregular thermal cycling on the power semiconductor device, which causes the IGBT junction temperature fluctuation to be more violent and complex, thereby accelerating its aging and reducing the overall reliability of the converter. In this paper, simulations based on thermal network and electro-thermal models are built to calculate the junction temperature of the IGBTs within the submodules on each bridge arm of the M3C, and their waveform characteristics are analysed, and then the rain-flow counting method is used to extract the thermal load of the IGBTs in one cycle, which contains three important parameters used for the life analysis.