Multiphysics Modeling, Analysis, and Validation of Immersion-Cooled Five-Level ANPC Inverters for Electric Propulsion

In the emerging transportation electrification applications, there is an increasing demand on concurrently pursuing high reliability, high energy efficiency, and high power density of power converters. Conventional cooling technologies, such as using bulky heatsinks or cold plates, have constrained further performance improvements of power converters. Based on an innovative immersion cooling technique, this paper presents a high-fidelity, multi-physics modeling and experimental validation framework for a 100-kW, five-level active neutral point clamped (5L-ANPC) power inverter, making it the first comprehensive study on this topic. The study begins by examining the electrical performance of the 5L-ANPC inverter, followed by the computation of semiconductor losses to be used as heat sources in subsequent thermal simulations. Afterwards, the immersion-cooled inverter is modeled and analyzed by conducting high-fidelity computational fluid dynamics (CFD) simulations. Various operating conditions and thermal design factors for the immersion-cooled 5L-ANPC inverter are considered, and the related impacts are investigated to characterize the thermal performance of the inverter. The results demonstrate significantly reduced semiconductor junction temperatures and more uniform heat distribution compared to conventional air cooling. The findings highlight the advantages of immersion cooling in thermal management, leading to higher output power and higher reliability. Finally, prototypes of air-cooled and immersion-cooled inverters are developed with intensive testing to compare the thermal performance. The multi-physics simulation results showing the superior performance of immersion cooling are also verified in the experiments.