Thermal Consideration and Design for a 200-kW SiC-Based High-Density Three-Phase Inverter in More Electric Aircraft

As advances in semiconductor, dielectric, and magnetic materials enhance the power density of power conversion systems, the emphasis on efficient cooling solutions becomes paramount. Effective thermal management is vital as it directly influences the power density and reliability of power inverters. This is especially crucial for high-altitude motor drives, given the challenges posed by reduced air density. This article provides a design process of thermal management for high-density high-power inverters. Thermal models for different scenarios are derived, and the hotspot temperature can be estimated under different cooling conditions. To demonstrate the proposed design process, a 200-kW three-level T-type propulsion inverter designed for an altitude of 7620 m (25 000 ft) is used to present the thermal designs. Several thermal mitigation techniques are also introduced. A critical finding is the potential for stagnating air spaces to produce localized hotspots in areas such as the busbar, gate-driver boards, and terminals. Historically, these hotspots have been overlooked, yet they can significantly degrade overall thermal performance and system reliability. To address the thermal issue of hotspots caused by stagnating air space, several solutions are proposed. Of these, the localized forced cooling air duct (AD) solution is selected in this work. By optimizing both internal and external airflows, the hotspot temperature in the stagnating air space is reduced by 37% using the designed AD without oversizing the overall cooling system. Moreover, based on full-power experimental thermal tests, we demonstrate that the inverter's hotspot temperature within a sealed enclosure can be kept below 130 degree celsius in an environment of 75 degree celsius and at an altitude of 7620 m. The culmination of our research validates the efficacy of the proposed design process.