Comprehensive System-Level Thermal Performance and Power Density Optimization in Enclosed Natural Convection PFC-LLC GaN Converters

GaN enhancement-mode high electron mobility transistors (e-HEMTs) excel at maximizing efficiency to possible extremes. With on-demand power density increase and efficiency approaching the saturation points, concerns regarding semiconductor reliability and thermal management intensify. This paper focuses on the two-stage GaN-based PFC-LLC converter, a prevalent topology in naturally-cooled consumer electronics, and explores solutions to address its thermal bottlenecks. An equilibrium thermal network is proposed, which is established by interconnecting thermal and electrical domains through accurate temperature-dependent loss characterization. These loss models are then transferred into the thermal network of the power converter. Furthermore, the concept of thermo-coupling, primarily developed in component-level studies, is expanded into system-level power converters. Various design subtleties, including proper component placement and PCB design aimed at enhancing GaN's junction-to-ambient thermal resistance ($R_{th,ja}$), are navigated. Eventually, this paper introduces a framework to achieve the maximum power density considering the thermal boundary, and presents a Pareto front of the multi-objective optimization (MOO) problem, explaining the power density and thermal performance trade-off. The proposed ideas can be used with other converters once their unique temperature-dependent loss models are determined. Finite element analysis (FEA) and experimental results are provided to support the claims.