Reduce Electric Vehicle Weight with Vicor High-Density Power Modules

Headquartered in Andover, Massachusetts, Vicor Corporation has been developing and manufacturing high-performance power modules for key industries such as communications, computing, defense and robotics since 1981. In the past six years, as the transportation industry has entered the era of electrification, Vicor has entered this field, providing compact, high-power density DC-DC power conversion devices to help the electric vehicle (EV) transformation.

Greg Green, director of automotive marketing at Vicor, explains: “If you’ve been following the automotive industry, electric vehicles have a weight issue. They are 15% to 33% heavier than a normal car, which causes a number of problems. So the industry is working to make vehicles lighter. Another issue is that the adoption rate of electric vehicles has plateaued for a few reasons. One of them is that consumers who are looking to buy an electric vehicle generally expect a range of about 540 kilometers, and the average range is currently about 100 kilometers less than that, which is causing people to reconsider whether they are ready to make the switch to electric vehicles.”

However, as Green acknowledges, reducing the weight of electric vehicles is no easy task. "There are several ways to reduce vehicle weight: shrinking or reducing the weight of the battery pack, eliminating low-voltage batteries, and shrinking the size of the DC-DC converter. The automotive world has been 12V since the mid-60s. However, 48V systems have gained interest because from an electrical safety perspective, the voltage must be below 60V to be safe, and 48V systems meet this requirement while leaving room for voltage fluctuations. The Tesla Cybertruck was the first vehicle to use a 48V power system in large quantities, which attracted a lot of attention, and since then, this field has developed rapidly."

Figure 1: High-performance power module

To address these challenges, Vicor has identified several key areas where its technology can have a significant impact. Through its high power density conversion devices, Vicor is working to enable miniaturization of battery packs, eliminate low voltage batteries, reduce the size of DC-DC converters, integrate smaller DC-DC converters into the battery housing, and introduce 48V regional architectures.

Green explains: “We use a power conversion process called zero voltage switching, which is very fast. This means we can go from zero power to full power at a rate of 8 million amps per second, taking power from the high-voltage battery, converting it to 48V and delivering it to the load faster than a standard 48V or 12V battery can deliver. This is critical because without the delay, we can eliminate the low-voltage battery entirely or significantly reduce its size, saving about 10 kg per vehicle.”

Another area Vicor is focusing on is shrinking the size of the DC-DC converter. Green added: "We're shrinking systems from 3-5 liters to 1-1.5 liters. Especially in passenger cars, space is critical, but even in larger vehicles, using less space provides more flexibility in vehicle layout design and other efficiency gains. To demonstrate this, we looked at the Tesla Model X, which has best-in-class power-to-weight and power-to-volume ratios, and Vitesco's new generation 4 system. We found that our system is two to three times better than both in terms of efficiency, power-to-weight ratio and power density. Our system shrinks the size of the DC-DC converter to the point where an engineer can easily imagine putting it inside the battery enclosure."

Essentially, Vicor's approach allows the DC-DC converter to be miniaturized and placed in a corner of the battery housing. This not only saves weight (because an additional metal housing is no longer needed to house it), but also allows the existing cooling system in the battery housing to cool the electronics. From a safety perspective, this approach also reduces the number of high-voltage cables leading out of the battery housing.

Figure 2: 48V regional architecture

As Green explains, the concept of 48V local architecture dates back to the late 1990s when the first hybrid electric vehicles emerged and were seen as a potential way to improve thermal efficiency. However, the technology didn’t see much development until Tesla unveiled the Cybertruck last October.

Green said: "This is mainly because most generators are 12V or 24V. The engineering and testing costs required to replace these generators are quite high, so there is some resistance. However, when you plug in the charging plug of an electric vehicle or hybrid vehicle, you automatically have a high-voltage battery. From a system perspective, it is easier for us to understand that 48V should be drawn from the high-voltage power source. The diameter and weight of 48V wire are only about 10% of the 12V wire. Voltage is similar to pressure in a way: low pressure means you need larger pipes, and high pressure means you can use smaller pipes. So 48V is a higher voltage, which means higher pressure. You can use smaller and lighter wires, which also use much less copper than 12V wires. In addition, the 48V design is also more efficient in dealing with heat losses because the 48V power supply can be brought to multiple points in the vehicle and converted locally to the 12V power supply required throughout the vehicle. This design brings weight advantages to the entire electric vehicle and reduces the complexity of the cooling system."

Figure 3: 48V designs can handle heat losses more efficiently

Combining all these elements—removing the low-voltage battery, shrinking the size of the DC-DC converter, and introducing a 48V region architecture in the line—Vicor calculates that engineers can save about 18 kilograms per vehicle.

Green said: “In an industry that often argues over saving a few grams of weight, this is a significant saving. But what does it actually mean to the user of the vehicle? We found that if a vehicle is 18kg lighter, the range can increase by 1 to 2.5 km, which may not seem like much. However, if this saving can lead to an additional 18kg of battery cells, the range can be improved by 5%. At the passenger vehicle level, this brings us closer to the ideal point that consumers would like to see to induce them to switch to electric vehicles. The same principle applies to larger vehicles, and in fact, the argument may be even more compelling in commercial vehicles, as saving 18kg may mean that an extra 18kg of cargo or passengers can be carried.”

With this in mind, it is clear that Vicor’s high power density DC-DC converter modules have the potential to provide greater flexibility and efficiency to power delivery networks, as these modules can be integrated into batteries due to their smaller size and reduced heat emissions.

Green concluded: "EV manufacturers can use these advantages to reduce vehicle weight and get closer to the ideal 540 km range, ultimately accelerating the adoption of EVs."