Although electric vehicles (EVs) have existed as long as internal combustion engine vehicles, they have only become mainstream in the past few years. As EVs emerge as the primary mode of transportation, battery range and faster charging speeds will become critical elements for the smooth functioning of the global economy. Improvements in these EV charging systems require advancements in multiple technological areas, including thermal management solutions. This article introduces the thermal management needs and developments for EVs, as well as the thermal management solutions offered by Same Sky.
Differences between AC and DC EV chargers
With significant advancements in EV technology and strong government support, the demand for EVs has been rising sharply. However, to further increase consumer acceptance of EVs, range and charging speed will become key factors in their purchasing decisions.
As the demand for faster chargers grows, charging methods have undergone changes, both large and small. One such change is the shift toward DC chargers. Since all battery systems use direct current (DC), the term "DC charger" might seem confusing. However, the critical difference lies in where the rectification from alternating current (AC) to DC occurs. A typical AC charger, commonly used in residential applications, functions like a versatile connector responsible for communication, filtration, and control of the AC power flow to the vehicle. The onboard DC charger then rectifies the power and charges the battery. In contrast, a DC charger performs the rectification before transmitting the power as a high-voltage DC source to the vehicle. The biggest advantage of DC chargers is that by moving the power conditioning hardware from the EV to an external structure, many weight and size constraints are eliminated.
With these constraints removed, DC chargers can easily integrate more components, thereby increasing their current throughput and operating voltage. These chargers use cutting-edge semiconductor devices for rectification, along with filters and power resistors, all of which generate significant heat. While filters and resistors are non-negligible heat sources, the largest heat-dissipating component in EV charging systems is the insulated gate bipolar transistor (IGBT), a semiconductor device widely used over the past few decades. This powerful device brings many opportunities to the charging field, but fully cooling it is a challenge that cannot be ignored.
Heat sources and design challenges for cooling systems
IGBTs are essentially a cross between a field-effect transistor (FET) and a bipolar junction transistor (BJT). Due to their high voltage tolerance, low on-resistance, fast switching speed, and excellent thermal stability, IGBTs are well-suited for high-power applications like EV chargers. Since IGBTs are used as rectifiers or inverters in these EV charging circuits, their frequent switching generates substantial heat.
Today’s cooling challenge lies in the fact that the heat dissipation of IGBTs has increased more than tenfold, from 1.2 kW thirty years ago to 12.5 kW today, with further increases expected. In comparison, the heat dissipation of today’s highest-power CPUs is about 0.18 kW, or just 7 kW/cm². This is a world of difference! Two factors aid in cooling IGBTs: their surface area is approximately twice that of a CPU, and they can operate at higher temperatures of up to 170°C versus 105°C for modern CPUs.
The most straightforward and reliable thermal management solution is a combination of heat sinks and forced air cooling. The internal thermal resistance of semiconductor devices like IGBTs is typically very low, while the thermal resistance between the device and the surrounding air is relatively high. Adding a heat sink significantly increases the heat dissipation area, thereby reducing thermal resistance, and forcing airflow over the heat sink further enhances its efficiency. Since the interface between the device and the air is the largest thermal resistance in the system, minimizing this resistance is critical. The advantage of this simple system is that, if properly installed, a passive heat sink will never fail, and fans - a mature and highly refined technology - are also highly reliable.
For high-density heat sources like IGBTs, liquid cooling options are also available. Water cooling systems may be more attractive due to their lower thermal resistance. However, they are more expensive, complex, and still rely on heat sinks and fans as the primary means of heat dissipation for the entire system. Therefore, directly cooling IGBTs with heat sinks and fans is the more desirable approach, and active research is underway to improve air cooling technologies for IGBTs.
Component layout, thermal monitoring, and environmental considerations
The key to the effectiveness of any cooling system lies in the layout of components to optimize airflow and distribute heat efficiently. Insufficient space between components can restrict airflow and limit the size of heat sinks. Therefore, critical heat-generating components should be strategically placed throughout the system to promote overall cooling efficiency.
While careful placement of individual heat-generating components is essential, the placement of thermal sensors is equally important. In large systems like DC EV chargers, real-time temperature monitoring enables active thermal management. Automatic adjustments to cooling mechanisms - such as limiting current output or adjusting fan speed - based on temperature readings can optimize performance and prevent overheating. However, these adjustments depend on the quality of their input data. If temperature sensors are poorly placed and yield inaccurate measurements, the system’s response will also be inaccurate.
On the other hand, since EV charging stations are typically installed outdoors and exposed to various environmental conditions, the design must include weatherproof enclosures with good ventilation to protect against rain and extreme temperatures. Additionally, airflow paths and vents must be designed to prevent water ingress without compromising airflow.
One of the most concerning external factors is the heat generated by sunlight on the charger enclosure, which can significantly raise the internal ambient temperature. While this is a valid concern, the most effective solution is surprisingly simple: a well-designed sunshade, combined with adequate airflow between the shading and the charging unit. This will significantly reduce the ambient temperature of the charger.
Increasing thermal management demands for EVs and charging stations
The global adoption rate of EVs over the past few years has been remarkable, with demand continuing to grow rapidly. As more EVs hit the road, the deployment of charging stations will surge accordingly. Fully functional, efficient charging stations are crucial for the charging infrastructure being actively built. Moreover, they must also be cost-effective, as cost is a significant factor in how quickly individuals and businesses integrate these chargers into homes and businesses.
Not only is the number of EVs and charging stations expected to grow, but the technology they rely on is also anticipated to evolve and improve. Considering the potential increases in charging power and capacity, the continuous changes in software and hardware standards, and the need to accommodate entirely new and unexpected developments, thermal management systems must be adaptable to meet changing demands.
At the most fundamental level, EV chargers face the same thermal management challenges as other high-density, high-power electronic devices. However, the power density of the IGBTs used in them, coupled with the rapidly growing demand, makes this challenge even more complex. As charging speeds and battery capacities advance rapidly, the requirements for manufacturing these chargers efficiently and safely will become increasingly stringent, placing higher demands on thermal management designers and engineers than ever before.
High-quality heat sinks and fans enhance EV thermal management efficiency
To improve the thermal management efficiency of EVs, Same Sky has designed heat sinks for EV charging applications, with custom sizes up to 950 x 350 x 75 mm. These heat sinks are large enough to passively handle less demanding charging needs or actively manage higher demands with forced air cooling.
Same Sky’s also offers a line of DC fans with a variety of axial fans and centrifugal blowers featuring frame sizes ranging from 20 mm to 172 mm and airflow rates from 0.33 to 382 cubic feet per minute (CFM). Same Sky’s DC fans come standard with auto-restart protection and use ball bearings, sleeve bearings, or Same Sky’s advanced omniCOOL™ system architecture. With a wealth of options and customization solutions, Same Sky’s DC fans are an ideal forced air cooling solution for EV applications. Additionally, Same Sky offers several IP68-rated waterproof axial fan models for harsh environments.
Same Sky’s DC axial fans are rated for 5, 12, 24, and 48 Vdc, with options for tachometer signal, rotation detector, and PWM control, and can reach speeds of up to 25,000 RPM. On the other hand, Same Sky’s centrifugal blowers have frame sizes ranging from 35 mm to 120 mm, are rated for 5, 12, and 24 Vdc, and offer airflow rates from 0.57 to 44.2 CFM. With various speed options up to 20,000 RPM, these blowers are ideal for high-back pressure applications. You can browse Same Sky’s full range of AC and DC fans at the following link: https://www.arrow.com/en/manufacturers/cui-devices/thermal-management/fans/blowers-and-fans.
Thermal design services transform cooling challenges into exceptional performance
In addition to offering a wide range of thermal management components, Same Sky provides industry-leading thermal design services. With the expertise of Same Sky’s professional thermal management team, cooling challenges are transformed into exceptional performance. Today’s electronic devices face severe thermal challenges due to increasingly compact designs, high power density, and the demand for enhanced performance. Same Sky’s cutting-edge thermal design services leverage advanced simulation tools and decades of expertise to identify potential hotspots, optimize airflow, and design efficient cooling systems tailored to customers’ specific needs.
For thermal simulation, Same Sky offers advanced computational fluid dynamics (CFD) modeling and analysis services, unlocking the power of thermal simulation to accurately predict and optimize airflow, temperature distribution, and heat transfer in your system. Moreover, since every design has unique cooling requirements, Same Sky also has the manufacturing capability to design custom thermal management solutions - including product customization and integration - and seamlessly incorporate them into your devices.
Additionally, Same Sky provides thermal management consulting services to maximize the effectiveness of your thermal management strategies. From PCB modeling and optimization to offering expertise in system, housing, and chassis design, Same Sky is committed to helping your devices perform at their best. Furthermore, Same Sky offers thermal testing and validation services to ensure the accuracy and reliability of your thermal designs. By validating simulation results with real-world testing, Same Sky helps you gain confidence in your device’s thermal performance and identify and resolve any potential discrepancies.
Conclusion
As EVs rapidly proliferate and charging technology continues to evolve, thermal management has become a critical factor affecting charging efficiency, safety, and battery lifespan. Future thermal management solutions for charging will not be limited to a single cooling method but will combine heat sinks, intelligent temperature control systems, AI predictive analytics, and other diverse technologies to address the thermal challenges posed by high-power fast charging. Only by establishing efficient, intelligent, and sustainable thermal management mechanisms can the full potential of next-generation EV charging systems be unlocked, accelerating the widespread adoption of green mobility. Same Sky offers both thermal management components and design services, enabling customers to quickly develop EV thermal management solutions and seize opportunities in the evolving EV industry.