Passive Thermal Management of Battery Disconnect Units for Fast-Charging Electric Vehicles: A Comparative Study of Phase Change Material Heat Transfer Configurations

Reducing charging time remains a critical challenge for the widespread adoption of electric vehicles (EVs). Limited charging infrastructure availability, combined with the long duration required for battery recharging, significantly affects user acceptance. As a result, fast-charging technologies are increasingly being introduced in both newly designed EV platforms and existing vehicles through retrofitting solutions. Despite their benefits, fast-charging systems impose substantial thermal loads on vehicle components, charging stations, and associated power electronics. Excessive heat generation can compromise performance, reliability, and safety, making effective thermal management a key design concern. Within the high-voltage architecture, the Battery Disconnect Unit (BDU) plays a vital role by monitoring and controlling the connection of the battery to the powertrain and charging system. Traditionally, BDUs are designed for conventional charging power levels; however, higher charging currents associated with fast-charging can lead to critical temperature rises beyond safe operating limits. Addressing this issue without extensive redesign of the cooling system or vehicle electrical layout is therefore highly desirable. This study proposes a passive thermal management solution based on a phase change material (PCM) heat transfer device to enhance the thermal robustness of the BDU during high-power charging events. The methodology combines experimental testing and numerical simulations. An initial experimental campaign is conducted to identify thermal hotspots within the BDU assembly under fast-charging conditions. The most thermally stressed component is then selected for targeted cooling enhancement. A detailed thermal model is developed using GT-Power software to predict system behavior and assess performance improvements. In addition, the paper presents a comparative study of different PCM heat transfer device configurations, evaluating their effectiveness in terms of temperature reduction, response time, and thermal uniformity. The results demonstrate that appropriately designed passive PCM solutions can significantly improve BDU thermal performance, enabling higher charging power capability while minimizing system complexity and integration effort.