Powering the next wave of Electric Vehicles
Making the move to 48V
With the rise of 48V architectures in electric vehicles (EVs), the automotive industry is at a tipping point.
Since the 1950s, 12V architectures have been standard for cars’ electrical and electronic (E/E) systems and batteries. Over the years, there have been proposals to move to higher voltages, including using 48V for Mild Hybrid Electric Vehicles (MHEVs) equipped with high-voltage starter generators, but 12V has remained dominant.
Now, the time has come for 48V as an in-car standard. Battery Electric Vehicles (BEVs), full hybrids, and plug-in hybrids have high-voltage batteries as their main power source, which can provide 48V3. Moving from existing 12V systems to 48V promises reductions in wiring harness size and cost, with improved efficiency.
Benefits of 48V Architectures
Compared to 12V, the main benefit of a 48V system consists of lower power losses, and hence higher efficiency. 48V architecture also enables improved thermal management, with less heat dissipated from resistive power losses. The reason for this goes back to the fundamentals: Ohm’s Law dictates that V=IR, while power losses in a conductor are given by P=VI. Combining the two, we see that resistive power loss is given by I2R – and is proportional to the square of the current.
For example, to deliver 1200W at 12V requires 100A, while at 48V this needs 25A. With current reduced by a factor of four, power losses are reduced by a factor of sixteen. A 48V rail can also reduce PCB size, because lower current can deliver the same amount of power.
Alternatively, we can use thinner wiring with 48V than with 12V. This thinner wiring has higher resistance than cables we would use with 12V, but keeps power losses down to an acceptable level due to the lower current. With thinner wiring, manufacturers can substantially reduce weight and cost of wiring harnesses. Reduced weight improves efficiency, enabling longer range – a major competitive advantage – and reduced emissions.
While the benefits achieved vary widely, we can say that shifting from 12V to 48V in a typical EV could reduce the car’s weight by around 45 to 70kg, and enable a longer range by circa 10km. Additionally, 48V systems can deliver more power than 12V alternatives – essential for the power-hungry features and gadgets in today’s vehicles.
Types of Vehicle Architectures
As well as shifting to 48V, cars’ electrical architectures are changing. In a traditional ‘flat’ architecture, there are repeated connections from the power source to each device, system and electronic control unit (ECU). As cars become more complex, with more ECUs, this has led to redundant cabling, and cost, weight and space issues.
To address this, many cars now use a ‘domain’ architecture, with cabling organised into functional domains. While this improves scalability and simplifies wiring, it still leads to inefficient cabling.
Taking this further, a ‘zonal’ architecture organizes wiring into several modular zones, with hardware gateways throughout the car, and ECUs linking to the nearest gateway, thus reducing the length of wiring required, and simplifying the system.
How to Overcome 48V Design Challenges
Migrating from 12V to 48V does create challenges for design engineers. This is partly because standards for 48V are less well-established, thus potentially requiring more engineering work to define a 48V system.
Engineers must consider the higher transient voltages with 48V, and how these can be contained. They must appraise the greater creepage and clearance distances needed for higher voltages, to prevent arcing between PCB traces. Additionally, 48V could lead to greater switching losses than in 12V systems.
With higher voltages and currents in a 48V system, there will be a more electrically noisy environment, requiring the right capacitors and other components to filter currents and cut RF emissions.
Key components of the 48V system
For a 48V system, several key components are required. Firstly, a battery: today’s BEVs already have a high-capacity 400V or 800V battery, which powers the 48V systems and the main powertrain. The vehicle requires an on-board AC-DC charger (OBC), that can handle high voltage alternating current (AC) at 7 to 11kW, and convert it to direct current (DC) at 400 or 800V to charge the battery.
Then, we need an on-board high voltage (HV) DC-DC converter, to take 400 or 800V from the battery, and convert it to 48V. To power legacy 12V components in the car, it may be practical to use another converter to go directly from 400/800V to 12V, or we can use multiple DC/DC controllers to provide 12V locally from the 48V rail. This approach maximises reductions in wire lengths.
Another key component is a 48V brushless DC (BLDC) motor, used for pumps, motors, and the internal combustion engine (ICE) starter in a hybrid vehicle.
Cost considerations
A BEV needs a variety of high voltage power electronics, including DC/DC converters, power MOSFETs and IGBTs, and power management ICs. Avnet Silica’s power semiconductor portfolio supports both traditional 12V and 48V architectures, including all these devices.
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SEE AUTOMOTIVEEven though the cost of these components in a 48V architecture is likely to be higher than that of a 12V system, the overall cost savings of moving to 48V will outweigh the higher bill of materials (BOM) cost.
While silicon is still the predominant choice in power electronics, another option is wide bandgap (WBG) semiconductors, such as Silicon Carbide (SiC) and Gallium Nitride (GaN). While these are typically higher cost than Silicon, they deliver important advantages, including improved power efficiency, higher operating temperature, higher power density, and smaller footprint.
Conclusions
The automotive/EV industry is already migrating from 12V systems to 48V. The two major advantages lie in the reduced weight and cost of wiring harnesses and the ability to provide higher power to in-car systems and devices.
Choosing the right components for 48V automotive applications depends on multiple considerations, including efficiency, power density, cost-effectiveness, and reliability.
Avnet Silica’s team possesses a wealth of expertise in power, automotive and EV sectors and are ready to help you. Engage with us to discover more about how we can support your specific needs.
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