Development of an Optimization Tool for the Geometry of Integrated Power Module Pin Fin Arrays Employed in Electrified Vehicles

Abstract

The mass-market adoption of electrification in the transportation sector mandates stringent and aggressive requirements in terms of cost, power rating, efficiency, power density, and specific density of power electronics. Modular packaging of power electronics is advantageous and thus ubiquitously used by the automotive industry. A trend of shrinking die sizes and increased integration is evident and will inevitably continue. The thermal management system has become ever more significant as it is one of the main obstacles to higher power densities. The cooling system must be cost-effective, simple, efficient, reliable, and compatible with system requirements.

Pin fins are a reliable and effective means of augmenting heat transfer. They rely on inducing turbulence, increasing the effective wetted surface, and accelerating fluid velocity. Unavoidably the pin fin array also produces an undesirable pressure drop that is commensurate to the pumping power required for the system. In this thesis, a tool is developed for the geometry optimization of pin fin arrays to dissipate the heat at a rate large enough to ensure junction temperatures do not exceed the maximum value possible at a minimal pressure drop. It is hoped that this tool would contribute to the multi-physics optimization and integration of power electronics for electrified vehicles. This optimization is confined to equalaterally spaced short pin fins, aspect ratios less than three. The tool employs empirical correlations since flow is too complex to solve analytically and numerical solutions or CFD-simulations are too time and computationally extensive.

The tool development is done in a comprehensive manner. Starting from the first principles of a two-level voltage source inverter's operation. Next, the inevitable power losses from the operation are explained and a method for their calculations is presented. Correlations in the literature related to both pressure drop and heat transfer are reviewed afterward. Then the methodology of the construction of the tool is explicated in detail. Employing a commercial power module to benchmark results; three scenarios with different flow rates and inlet temperatures are optimized for. Simulations in ANSYS Fluent are run to verify the accuracy of correlations used in the tool. Comparing the optimized geometry of pin fins to the original benchmarking geometry it is evident that employing this tool on a per-application basis provides superior performance.