Electric vehicles have a weight problem that cannot be solved with traditional methods

Author: Noa Margolin, R&D Engineer, Vicor Corporation

High-density power modules allow 48V systems to reduce weight and power losses

Battery-powered electric vehicles (EVs) have a serious weight problem. Many EVs weigh up to 33% more than their internal combustion engine counterparts. Thus, the president of the National Transportation Safety Council in the US stated: “The Ford F-150 Lightning truck weighs between 900 and 1.400 kg more than the non-electric version.” Furthermore, the National Bureau of Economic Research concluded that adding 450 kg to a vehicle increases the risk of fatality in the event of an accident by around 47%.

As a result, automakers face major limitations when trying to design EVs with more autonomy, safety, and electronic content. This is one of the most formidable R&D challenges this sector has ever faced.

Despite the magnitude of this challenge, concern among manufacturers, consumers and legislators can be mitigated if conventional EV power networks, characterized by their overweight, are replaced by 48V zonal architectures in which a 48V bus replaces the previous 12V system. Deploying a zonal architecture based on high-density power modules will reduce weight in three ways. This new architecture will facilitate the transition from wiring with a thick diameter to a much thinner one, thus reducing its weight by up to 85%. Additionally, low-voltage auxiliary batteries can be removed and virtualized with power modules, thus completely eliminating battery weight. Finally, the new power module-based power network optimizes the thermal management system and reduces its weight by up to 33%.

Therefore, the transition to a zonal architecture as an alternative to the traditional centralized architecture significantly reduces the weight and improves the overall efficiency of the power system.

Adoption of 48V: an obvious and pending improvement in EVs

Figure 1: Conversion to a 48V system reduces the total current consumption in the vehicle from more than 250A to less than 75A without affecting the electrical content of the vehicle. Since 1908, the demand for power in automobiles has grown exponentially with the incorporation of electronics in vehicles. In the 1960s, manufacturers increased the voltage from 6V to 12V, causing a drop in current for the first time in 60 years. Currently, most manufacturers continue to use the 12V bus despite the demand for more current. In 2023, Tesla became the first manufacturer to announce full adoption of the 48V bus throughout the vehicle, which will greatly decrease current demand.

New vehicles have incorporated new electronic circuits in each design cycle in order to improve protection, safety and autonomy. Each function that is added increases consumption and, if the battery is fixed and standardized, this has translated into an exponential increase in current. As the current trend demonstrates (Figure 1), the power grid based on a centralized architecture is unsustainable. The only way to address the increasing need for power and at the same time provide sustainable levels of current, minimizing the weight of the wiring, is to increase the working voltage up to 48V through a zone architecture.

Current EVs are powered by a high-voltage main battery (generally 400V or 800V) that must power not only the electric traction motor but also a huge number of low-voltage loads, such as air conditioning, car heating, seats and infotainment systems. A power network reduces the high voltage to the 48V and 12V of the auxiliary batteries that power these subsystems.

Adopting a 48-zonal architecture presents an opportunity taking into account Ohm's Law: For the same power supply, a 12V source requires a fourfold increase in current compared to a 48V source. Therefore, the cable for 12V is also usually four times thicker than for 48V.

Figure 2. Today's automobiles use two types of power networks: the centralized 12V architecture and the rapidly growing 48V zonal architecture. The first depends on thick 12V wiring, while the second uses thin 48V wiring that is much lighter, reduces heat loss and reduces current by up to four times.

The decline of centralized 12V architecture

The centralized 12V system has been the traditional power architecture used in automobiles since the 1960s. This architecture consists of a bulky box in a housing containing a set of discrete components, including all DC/DC converters. high voltage to go from 48V to 12V. Thick, heavy cables are needed to carry the 12V current to the charging points. Added to this is that, due to the inherent inefficiency of traditional DC/DC conversion, this centralized power system generates a significant amount of heat from the case, which often requires intense liquid cooling which in turn adds more weight. .

The adoption of 48V high-density power modules can be applied at the extremes to efficiently convert up to 12V at charging points. Manufacturers thus have the necessary flexibility to gradually transition charging devices from 12V to 48V over time. This helps you quickly take advantage of the benefits of using 48V with minimal alteration to the system architecture.

48V zonal architecture reduces heat and current loss

This innovative 48V zonal architecture system takes advantage of Ohm's Law and represents a paradigm shift for the sector: the DC/DC conversion takes place closer to the charging points and not within the centralized box. According to this approach, converting high voltage to 48V allows for a safe 48V bus throughout the vehicle. The conversion from 48V to 12V is done at the charging point. By carrying current at 48V instead of 12V, cables can be thinner, lighter and significantly more economical (Figure 2). This smaller, more flexible cable is also easier to install inside the vehicle. This technique also more evenly distributes heat loss generated by DC/DC converters across the vehicle, thus enabling the potential use of chassis-mounted air cooling and heat conduction solutions.

Calculation of weight savings

The 48V zonal architecture better adapts to the increasing power demand of EVs, while reducing vehicle weight in three ways:

1. Wiring: ~85% weight reduction

Adopting the 48V zonal architecture means replacing traditional thick 4 gauge 273g/m 12V cables with 10 gauge 27g/m 48V cables. This reduces the weight of the wiring by approximately 85%.

2. Elimination of auxiliary battery: weight reduction Up to 100%

Figure 3: Power modules offer faster transient response than 12V lead-acid batteries, creating a virtual battery that can replace the old, heavy 12V battery.

A zonal architecture based on power modules allows you to accelerate the response of the DC/DC converter to transients by creating a virtual battery. Therefore, 12V/48V zonal power modules reproduce the characteristics of 12/48V low voltage batteries, in addition to completely eliminating the physical 12V battery, thus saving 100% of its weight.

3. Feeding system optimization: ~33% weight reduction

Figure 4: The size of the centralized box can be reduced by using power modules and a zonal architecture because heat can be dissipated more efficiently at the endpoints where the 48V is converted to 12V loads.

Replacing the centralized system with a zoned system moves the conversion from 48V to 12V from the box to the charging points. The new power system box based on high-density power modules to supply 48V will be up to 33% smaller, so its weight can be reduced by up to a third (33%).

In a traditional centralized 12V system, the discrete components generate a high ambient temperature inside the case, while the power system based on high-density power modules generates less heat and the modules at the point of load can be cooled efficiently in the chassis. These improvements allow the weight of the liquid cooling system to be reduced by up to 7%.

Transform weight into an opportunity

Automakers benefit in several ways from zonal architecture. To illustrate this, let's think about the effect that reducing weight will have on the vehicle's greater autonomy.

The weight of the vehicle influences its consumption and its autonomy. However, the extra weight can mitigate its effect on range if it is used to increase battery size. The additional battery provides greater energy storage, and therefore improves autonomy.

According to a study carried out by Vicor, zonal architecture based on high-density power modules can reduce vehicle weight by up to 18 kg (Table 1). When this weight is replaced by
With 18 kg of cells in the battery, the EV's range can be increased up to 6.400 km per year, without a net weight gain.

This figure is significant considering that, in the case of the US, a driver travels an average of 23.000 km per year according to the Federal Highway Administration. Therefore, the use of the 48V zonal architecture can reduce the annual charging time by up to 30% (Table 2) and increase the distance that the vehicle can travel with each charge.

Table 1: The combination of a 48V zonal architecture and high-density power modules saves about 18kg of weight in compact electric SUVs.

Table 2: Improved range provides drivers with greater distance per charge, thus reducing the number of charges required per year.

Innovate to eliminate

Electric vehicles are overweight and this trend is neither sustainable nor beneficial for EV demand growth. The centralized 12V architecture, with its discrete box and components, needs to evolve towards a 48V zonal architecture to optimize the EV power network and thermal management system. The zonal architecture can increase the range up to 6.400 km per year or can be used to increase the safety of electronic functions.

The most efficient zonal architectures use small, lightweight converters at the point of load. Modules with high levels of power density and efficiency are the best choice for 48V to 12V conversion.

Given the complexity of automotive power electronics today, manufacturers need to be creative to save weight and increase performance. Vicor, the leader in high-performance power modules, facilitates innovation and creativity. Vicor's compact power modules, architectures and topologies offer automakers flexible and scalable power solutions for high voltage conversion throughout the vehicle. These power modules are easy to install and are the alternative to the traditional discrete designs used until now in centralized power systems. Small and compact power modules are the best option and a natural component for a 48V zonal architecture, which is the power network of the future for the automotive industry.