Single-Phase Dielectric Fluid Thermal Management for Power-Dense Automotive Power Electronics

This article describes the design and performance of a dielectric fluid cooling concept for automotive power electronics. The concept combines a low-thermal-resistance package (which eliminates metalized ceramic substrates) with a high-performance convective cooling strategy (slot jets impinging on finned surfaces). Modeling was first used to design the cooling system to maximize thermal performance and minimize pumping power. A prototype was then fabricated, and experiments were conducted to validate the model predictions using three fluids at various fluid flow rates (16.7 cm3/s [1 L/min] to 68.3 cm3/s [4.1 L/min]) and inlet temperatures (30 °C and 70 °C). The final design was compact (120-cm3 total volume, including heat exchanger and conceptual power modules) and cooled 12 devices (e.g., silicon carbide [SiC]). The validated model was then used to predict the junction-to-fluid thermal resistance and pumping power for various conditions, including -40 °C fluid temperature. The results predict thermal resistance values as low as 19 mm2·K/W is possible using the dielectric fluid cooling approach. The dielectric fluid cooling system is predicted to provide thermal resistance and pumping power values that are approximately 56% and 90% lower, respectively, compared to an automotive power electronics cooling system. Moreover, the dielectric fluids can be used for direct cooling of the bus bars, which can be an effective capacitor and gate driver cooling strategy and enable the use of new driveline fluids tailored for this application.