Battery thermal management strategy utilizing a secondary heat pump in electric vehicle under cold-start conditions

When an energy storage system (ESS) operates in cold conditions, the power and capacity of the battery critically fade. Therefore, an appropriate battery thermal management strategy (BTMS) is essential to prevent severe driving range loss at low ambient temperatures. However, none of existing studies considered the effect of BTMS on the driving range from a systematic perspective. Thus, we evaluated the trade-off between the performance enhancement by ESS heating and the additional energy consumption for ESS heating. We suggested and analyzed three BTMSs combined with a secondary heat pump: self-heating, active heating, and heat recovery. Active heating of the battery augmented the driving range of the EV by up to 18.8% over the self-heating strategy when the battery was used to full depletion, whereas the heat recovery strategy reduced the state-of-charge (SOC) decrease and thus increased EV driving range in nondepleted conditions. Furthermore, battery preheating with the heat pump achieved a temperature rise of 20 degrees C within an hour, consuming 38.4% less battery power than with conventional electric heater preheating. We expect this study contributes to the range extension of EV by suggesting the optimal BTMS depending on the driving conditions.