Refrigerant Cycle with Latent Heat Storage for Battery Cooling
High power charging stations with charging powers of up to 350 kW are introduced to shorten the charging times of electric vehicles to less than 15 minutes. However, a significant amount of heat is generated in the traction battery during fast charging. This requires a sophisticated thermal management system for battery cooling. Valeo and Virtual Vehicle have designed and studied a refrigeration system with phase change material storage to prevent overheating of the battery cells.
Battery cooling normally uses a refrigerant cycle in the thermal management system (TMS), which is also increasingly used as a heat pump. This heat pump uses heat sources such as the powertrain, the battery or the ambient air, thus increasing the range when the weather is cold.
The following figure shows the structure of the battery with the integrated refrigeration plate, which is cooled by the refrigerant cycle.
In addition to battery cooling and heating, the TMS also has other tasks, such as cooling and heating the powertrain and cooling, heating and dehumidification of the cabin air. These different requirements must be considered in the development of the TMS and its control system.
Phase Change Material (PCM) is characterised by its ability to absorb or release large amounts of heat during the phase change and is therefore well suited as a heat storage or “cold storage.”
This attribute has been used to increase the total available cooling capacity by switching between the following two operating modes:
Cabin cooling and loading the PCM storage:
In this case, the battery path is not active, instead the refrigeration cycle is used to cool the phase change material (PCM) storage to a temperature below the phase change, thus “charging” the cold storage. At the same time, the refrigerant pump is active to cool the passenger cabin via the evaporator.
Battery cooling and cabin cooling via PCM storage:
Here, the cabin is cooled with the use of the PCM cold storage unit. This means that the refrigerant cycle can be used exclusively for cooling the battery. This significantly increases the battery cooling capacity compared to cooling the battery and cabin at the same time due to the higher suction pressure, which enables a higher compressor power.
By using these two operating modes, the average power for battery cooling could be increased by 22% compared to a state-of-the-art reference system, while maintaining the same cabin cooling power.
Conclusion: Modern charging technologies also require further development of thermal management systems to guarantee the safety of various components – especially the battery. Together with industrial partners such as Valeo, VIRTUAL VEHICLE is researching technologies that make electromobility and mobility in general safer and more efficient.
For more information, see the article that was published in the ATZ in September 2023.