Liquid-Cooled Charging Cables: A Breakthrough in Ultrafast EV Charging
The electric vehicle (EV) revolution is accelerating, with manufacturers pushing the boundaries of battery technology and charging infrastructure to eliminate range anxiety and reduce charging times. However, as EVs demand faster charging speeds, a critical bottleneck has emerged: thermal management in charging cables. High currents generate significant heat, which can degrade cable insulation, shorten equipment lifespan, and pose safety risks. Traditional solutions, such as increasing cable diameter, lead to heavier, less user-friendly charging cables. To address this challenge, researchers from the College of Electronic Information and Engineering at Taiyuan University of Science and Technology have conducted a groundbreaking study on the thermal performance of high-power liquid-cooled charging cables. Their findings, published in Guangdong Electric Power, offer a comprehensive analysis of how different factors influence cable temperature and current-carrying capacity, paving the way for safer, more efficient ultrafast charging systems.
The study, led by Jia Lumeng, Li Hongjie, Li Xutao, Deng Ruoyu, Du Jianfeng, and Wang Anhong, focuses on the development of a finite element simulation model that integrates electromagnetic, thermal, and fluid dynamics fields. This multi-physics coupling approach allows for a detailed examination of the complex interactions between electrical current, heat generation, and cooling efficiency. The researchers specifically investigated the impact of cooling medium type, cooling channel structure, and coolant flow rate on the performance of charging cables under ultrafast charging scenarios. By doing so, they aimed to optimize the design of liquid-cooled cables without increasing the cross-sectional area of the cable core, thus maintaining a lightweight and manageable cable for users.
One of the primary challenges in ultrafast charging is the significant increase in thermal effects. As charging currents rise, the resistive losses in the cable core generate more heat, leading to higher temperatures. If not properly managed, these elevated temperatures can cause the insulation materials to degrade, potentially leading to catastrophic failures. The researchers noted that conventional methods of increasing the cable’s cross-sectional area to handle higher currents are impractical due to the resulting weight and bulkiness. Instead, they proposed the integration of active cooling channels within the cable structure to enhance heat dissipation.
The team’s simulation model was based on a real-world charging cable used in electric vehicles, with a core cross-sectional area of 70 mm². They simplified the cable model by assuming perfect contact between layers and ignoring minor components like shielding and filler materials. This simplification allowed for more accurate and computationally efficient simulations. The model considered the cable’s electromagnetic field, which generates heat due to resistive losses, the thermal field, which governs heat transfer through conduction, convection, and radiation, and the fluid field, which describes the flow of the cooling medium.
To validate their model, the researchers first simulated the temperature distribution in a traditional charging cable without any cooling channels. They found that under a current of 200 A, the core temperature reached 50 °C, which is close to the maximum allowable operating temperature of 90 °C for the insulation material. This result highlighted the need for effective cooling solutions, especially as charging currents increase to 600 A or higher.
The next step was to introduce an active cooling channel into the cable design. The cooling channel, made of a flexible plastic tube, was placed alongside the cable core. The researchers tested various cooling media, including air, water, transformer oil, and ethylene glycol aqueous solution. Each medium has different thermal properties, such as density, thermal conductivity, and specific heat capacity, which affect its cooling efficiency.
The results were striking. When air was used as the cooling medium, the core temperature dropped to 81 °C at 600 A, a significant improvement over the uncooled cable. However, liquid cooling proved to be far more effective. Water, with its high thermal conductivity and specific heat capacity, achieved the best cooling performance, reducing the core temperature to 59.9 °C. Ethylene glycol aqueous solution and transformer oil also performed well, with core temperatures of 60.1 °C and 60.3 °C, respectively. These results demonstrated that liquid cooling is superior to forced air cooling in managing the thermal load of high-power charging cables.
Despite the excellent cooling performance of water, the researchers noted a significant drawback: its low freezing point. Pure water freezes at 0 °C, making it unsuitable for use in cold climates. To overcome this limitation, they recommended the use of ethylene glycol aqueous solution, which has a lower freezing point and better thermal stability. Ethylene glycol is commonly used in automotive antifreeze and coolant systems, making it a practical choice for EV charging applications.
The structure of the cooling channel also played a crucial role in the cable’s thermal performance. The researchers varied the ratio of the cooling channel’s cross-sectional area to that of the cable core, ranging from 0.5 to 2.0. They found that as the ratio increased, the core temperature decreased significantly. At a ratio of 1.0, the core temperature was 68.8 °C, but it dropped to 37.8 °C when the ratio was increased to 2.0. This reduction in temperature was attributed to the increased flow rate and heat transfer efficiency of the cooling medium. However, the researchers noted that the benefits of increasing the cooling channel size diminish beyond a certain point. For example, the temperature difference between a ratio of 1.5 and 2.0 was relatively small, suggesting that there is an optimal balance between cooling performance and cable size.
Another important factor in the cooling system’s performance is the flow rate of the coolant. The researchers tested five different flow rates: 0.05 m/s, 0.1 m/s, 0.15 m/s, 0.2 m/s, and 0.25 m/s. They found that as the flow rate increased, the core temperature decreased, but the rate of decrease slowed down at higher flow rates. At a flow rate of 0.05 m/s, the core temperature was 49.7 °C, but it dropped to 46.6 °C at 0.25 m/s. The most significant temperature reduction occurred between 0.05 m/s and 0.15 m/s, after which the temperature change became minimal. This suggests that there is an optimal flow rate for the cooling system, beyond which the additional energy required to pump the coolant does not provide a proportional benefit in cooling performance.
The researchers concluded that the ideal flow rate for the cooling medium is between 0.1 m/s and 0.15 m/s. At this range, the cooling system provides the best balance between thermal performance and energy efficiency. They also noted that the optimal flow rate may vary depending on the specific application and environmental conditions, but their findings provide a solid foundation for further optimization.
One of the key advantages of liquid-cooled charging cables is their ability to maintain a lower core temperature while handling higher currents. The researchers demonstrated that with a core cross-sectional area of 70 mm², a cooling channel-to-core area ratio of 1.25, and a coolant flow rate of 0.1 m/s, the cable could achieve a current-carrying capacity of 600 A, with a core temperature of 49.7 °C. This represents a significant improvement over traditional cables, which would require a much larger cross-sectional area to handle the same current without overheating. The ability to increase the current-carrying capacity without increasing the cable size is a game-changer for ultrafast charging, as it allows for faster charging times without compromising user convenience.
The implications of this research are far-reaching. As the demand for ultrafast charging continues to grow, the development of efficient and reliable cooling solutions will be essential. Liquid-cooled charging cables offer a promising solution, combining high current-carrying capacity with excellent thermal management. The findings of Jia Lumeng and her colleagues provide valuable insights into the design and optimization of these cables, helping to ensure that the next generation of EVs can be charged quickly and safely.
In addition to improving the performance of charging cables, the research also highlights the importance of multi-physics modeling in the design of complex systems. By integrating electromagnetic, thermal, and fluid dynamics simulations, the researchers were able to gain a deeper understanding of the interactions between different physical phenomena. This holistic approach is essential for developing innovative solutions to the challenges facing the EV industry.
The study also underscores the need for continued research and development in the field of thermal management. While liquid-cooled cables represent a significant advancement, there is still room for improvement. Future work could focus on optimizing the cooling channel design, exploring new cooling media, and developing more efficient pumping systems. Additionally, the integration of smart sensors and control algorithms could enable real-time monitoring and adjustment of the cooling system, further enhancing its performance and reliability.
The transition to electric mobility is not just about replacing internal combustion engines with electric motors; it requires a complete rethinking of the entire transportation ecosystem. From battery technology to charging infrastructure, every component must be optimized to deliver a seamless and sustainable user experience. The research conducted by Jia Lumeng and her team at Taiyuan University of Science and Technology is a prime example of how interdisciplinary collaboration and advanced simulation techniques can drive innovation in the EV sector.
As the automotive industry continues to evolve, the role of academic institutions and research organizations will become increasingly important. By bridging the gap between theoretical research and practical applications, these institutions can help accelerate the adoption of new technologies and bring the benefits of electric mobility to a wider audience. The work of Jia Lumeng and her colleagues is a testament to the power of scientific inquiry and the potential for technology to transform our world.
In conclusion, the study on the thermal performance of high-power liquid-cooled charging cables provides a comprehensive and detailed analysis of the factors that influence cable temperature and current-carrying capacity. The findings highlight the superiority of liquid cooling over forced air cooling, the importance of optimizing the cooling channel structure, and the existence of an optimal flow rate for the coolant. These insights are crucial for the development of safer, more efficient, and user-friendly ultrafast charging systems. As the EV market continues to grow, the innovations described in this research will play a vital role in shaping the future of electric mobility.
Jia Lumeng, Li Hongjie, Li Xutao, Deng Ruoyu, Du Jianfeng, and Wang Anhong, College of Electronic Information and Engineering, Taiyuan University of Science and Technology, Guangdong Electric Power, doi: 10.3969/j.issn.1007-290X.2024.06.013