Assessing Thermal Buffering Half-Bridge Interconnects for Engine Compartment Traction Inverter

The Army Research Laboratory has developed a novel power electronic interconnect capable of temporarily storing waste thermal energy to better load level transient power profiles, resulting in delayed and more uniform temperature rise. The interconnects are formed by infiltrating a porous metallic foam with a low melting temperature metal (LMPM). ARL has demonstrated interconnects with melting points ranging from 30 to 120°C. Selecting the appropriate temperature is key to fulfilling the intended purpose, which could include cyclic buffering, intermittent levelling, or failsafe/one-shot temperature control of power electronics. Knowledge of the intended transient power profile is critical, including heat flux density, duty factor and cycle period. In a traction inverter, the dissipated thermal power of the power electronics is related to the switching characteristics of the half-bridge modules performing the power conversion. While the thermal oscillations at the timescale of the switching frequency do not propagate far from the device junctions, the envelope responding to changes in the duty factor and current draw presents a stochastic transient profile that can be managed by thermal storage elements. In our application the thermal management is complicated by locating the inverter within the engine compartment – near the rotating machines and cooled by the same 105°C coolant. Predicting the potential benefit of LMPM interconnects requires synthesizing mission-relevant drive loading requirements with an austere thermal budget and experimentally measured composite material thermal properties. We present a model-based design that shows the potential benefits of LMPM interconnects under heavy vehicle acceleration in Army-relevant scenarios.