A Study of the Energy Consumption of a Battery Cooling System by Different Cooling Strategies

The High Voltage (HV) batteries that are used today in Hybrid Electric Vehicles (HEV), Plug-In Hybrid Electric Vehicles (PHEV), and Electric Vehicles (EV) utilize cooling systems to keep the battery packs within optimal operating temperature ranges. Manufacturers spend a generous amount of money to design these cooling systems to keep the batteries within these safe operating temperature requirements during harsh conditions, such as extreme cold and heat. Desert conditions can reach an average ambient temperature of 40°C. The temperature of the batteries can affect their performance, reliability, and the health of each cell. The Lithium Iron Phosphate (LiFePO4) battery systems manufactured by A123 Systems Inc. operate between 20-50°C for optimum performance. The thermal distribution among all batteries cells within a battery module is also important. Even a 3-4°C difference in cell temperature can result in reduced performance and potentially damage individual cells. Lithium iron phosphate batteries have a potential safety concern when it comes to temperature; if the temperature is too high, the batteries have a potential to go into thermal runaway and catch fire. This research effort has been conducted at West Virginia University (WVU) to evaluate how different cooling systems compare in cooling batteries during various battery usage cycles. The two systems that were evaluated were a 50/50 ethylene glycol water mixture recirculating coolant system and an R-134A refrigerant system. The research evaluated the impact on battery performance and energy consumption from the system using modeling and simulation. Prototype cooling systems were then fabricated and experiments were conducted using a representative aluminum block to simulate the thermal mass of the battery modules. The experimental data were used to validate the results of the simulation models. Matlab Simulink was used to simulate a PHEV hybrid-electric vehicle and determine the impacts from the thermal cooling system over various drive cycles. The thermal models were validated using experimental bench tests to confirm critical input data and verify that results were valid. The team used this simulation package and model to design the cooling system for the West Virginia University (WVU) EcoCAR 3 PHEV Chevrolet Camaro. Through the results of this thesis it was found that the 50/50 ethylene glycol system would use roughly three times less energy than the R-134a refrigeration system over the aggressive US06 drive cycle