Measured Thermal Performances at Brick and Module Levels in a Battery Pack of a Mid-Size Electric Vehicle under WLTC and FTP Cycles

Performances of battery electric vehicles (BEV) are affected by the thermal imbalance in the battery packs under driving cycles. BEV thermal management system (VTMS) should be managed efficiently for optimal energy consumption and cabin comfort. Temperature changes in the brick, module, and pack under the repeated transient cycles must be understood for model-based development. The authors conducted chassis dynamometer experiments on a fully electric small crossover sports utility vehicle (SUV) to address this challenge. A BEV is tested using a hub-type, 4-wheel motor chassis dynamometer with an air blower under the Worldwide Harmonized Light Vehicles Test Cycle (WLTC) and Federal Test Procedures (FTP) with various ambient temperatures. The mid-size BEV with dual-motor featured 80 thermocouples mounted on the 74-kWh battery pack, including the cells, upper tray, side cover, and pack cover. The authors analyzed battery pack temperature distribution behavior by changing the battery’s initial state of charge (SOC) and cell temperatures.

Performance metric data such as battery voltage, current, SOC, pack temperature, coolant properties, pressure drop, and flow rate are recorded and analyzed. The results show the temperature variations under diverse driving conditions, with an average difference of 1°C between modules and 2.3°C between bricks in module 1, and a maximum temperature difference of 3.9°C is recorded in the battery pack. The results provide valuable insights into the optimal operational range for maintaining battery pack temperature stability. The measured results can provide a fundamental understanding of the peak temperature location on the brick-to-brick and pack-to-pack variation under transient cycles. These results provide a fundamental understanding of the thermal performance of battery brick, module, and pack, which can be used to develop a VTMS model.