Impact of Immersion Cooling on Balancing Semiconductor Thermal Distribution in NPC Multilevel Converters for Transportation Propulsion

Neutral point clamped (NPC) multilevel converters have been intensively utilized in many industry sectors, such as transportation electrifications, data centers, renewable energy generation, industry automation, and others. However, one major drawback with NPC converters is the unbalanced loss distribution among the semiconductor switches, which limits the maximum allowable output power and output frequency of the converters. In this paper, a novel immersion cooling technology is developed for NPC converters for transportation electrification applications, particularly for electric aircraft propulsion systems. The immersion cooling technology helps to balance the semiconductor thermal distribution with homogenous cooling, in addition to providing enhanced dielectric insulation capability for power converters operating at high altitude for aviation applications. This concept and the performance advantages are verified by comparing the immersion cooling case with the conventional heatsink cooled converters.