Silicon carbide based traction inverter cooling in electric vehicle using heat pipes

Abstract

Power train in electric vehicles is provided with assortment of power electronics including traction inverter to control, monitor and deliver electric power from battery system to electric motor as per vehicle needs. Inverter technology based on Silicon Carbide (SiC) semiconductor provide lower switching losses, can handle high power densities and can operate at very high junction temperatures ∼ 200 °C, which enables air cooling for such system viable. This project investigates the technical feasibility and the potential of an air-cooled traction inverter, for mid-sized passenger vehicles, with very high heat fluxes (∼35 W/cm2) and heat loads exceeding ∼ 2.2 kW. Heat pipe based air cooled heat sink has been evaluated for thermal management of SiC inverter for traction purposes in electric vehicles. Traction inverter was equipped with 3x SiC power modules, each with 350 W heat load (∼17 W/cm2 heat flux) totaling 1050 W, and operating in 85 °C ambient. Based on analysis of different design options, remote heat pipe heat exchanger was chosen as optimal design with best performance and volume/area ratio. Heat pipe system with copper–water heat pipe configuration and air cooled aluminum sheet metal based heat sink arrangement was designed in segmented form to dissipate asymmetric heat loads (65 % top, 35 % bottom) output by two faces of each SiC power module. Top surface of each chip was cooled by separate heat sink, each with 2x U-shape heat pipes while bottom faces of three chips have common heat sink with 6x L-shape heat pipes. Complete cooling system was put together using system of copper blocks that provide housing for SiC power modules while allowing for integration of cooling module into inverter housing, keeping IP6 K4K sealing requirements. Proposed solution was able to keep junction temperature < 142 °C against requirement of 175 °C, provide thermal uniformity within ∼ ±5 °C, was able to handle maximum power surges double of nominal loads, qualify for start-up from frozen state and was able to handle temperature cyclic loading without showing any performance degradation. Heat pipe based air cooling system for traction inverter, in particular, and overall vehicular power electronics, in general, will provide dedicated and modular cooling system approach, which can be located with relative ease and simplicity as compared to liquid cooled system while achieving lower system cost. Furthermore, such systems will provide operational safety against leaks, runtime reliability and lifetime longevity which is critical in automotive.