“Manufacturers of cars, trucks, buses and motorcycles are rapidly electrifying their vehicles to improve the fuel efficiency of internal combustion engines and reduce carbon dioxide emissions. There are many electrification options, but most manufacturers do not choose a full hybrid powertrain, but choose a 48-volt mild hybrid power system. In addition to the traditional 12V battery, the mild hybrid system also adds a 48V battery.
Manufacturers of cars, trucks, buses and motorcycles are rapidly electrifying their vehicles to improve the fuel efficiency of internal combustion engines and reduce carbon dioxide emissions. There are many electrification options, but most manufacturers do not choose a full hybrid powertrain, but choose a 48-volt mild hybrid power system. In addition to the traditional 12V battery, the mild hybrid system also adds a 48V battery.
This can increase the power by 4 times (P = V? I) for heavy loads such as catalytic exhaust gas purifiers. The 48V system can supply power to the hybrid engine, which saves fuel while accelerating faster and more smoothly to improve vehicle performance. The additional power supply not only provides support for steering, braking and suspension systems, but also adds new safety, entertainment and comfort features.
The introduction of a 48-volt mild hybrid power system will have great advantages once the design is completed. Overcoming the hesitation to retrofit the long-existing 12-volt power supply network (PDN) may be the biggest challenge. Changing the power supply usually requires new technologies that must be tested extensively, and may also require new suppliers that can supply power in accordance with the high safety and high quality standards of the automotive industry.
But the data center industry found in the process of shifting to 48V PDN that the advantages of doing so far outweigh the switching costs. For the automotive industry, the 48V mild hybrid power system has brought a way to quickly introduce new vehicles with lower emissions, longer driving range, and lower fuel consumption. In addition, it also provides exciting new design options for improving performance characteristics and reducing carbon dioxide emissions.
How to maximize the 48V power supply network
Adding a 48V battery to power heavier powertrain and chassis system loads provides engineers with various options. There is now an option to increase the system, which can directly handle 48V input, or retain the original 12V electromechanical loads such as pumps, fans, and motors, without the need to convert 48V to 12V through a regulated DC-DC converter. In order to manage changes and risks, while the existing mild hybrid power supply system is gradually increasing the 48V load, it still uses a large centralized multi-kilowatt 48V to 12V converter to provide the entire car’s 12V power supply to the 12V load. However, this centralized architecture not only does not fully utilize the advantages of the 48V PDN, but also does not take advantage of the advanced converter topologies, control systems, and packaging available today.
Figure 1 Traditional 12V centralized architecture Figure 2 48V distributed architecture
Most of these centralized DC-DC converters (Figure 1) are bulky because they use earlier low-frequency switching PWM topologies. In addition, they can also bring a single point of failure to a large number of critical powertrain systems.
Another architecture that needs to be considered is the use of modular power components for distributed power supply (Figure 2). The power supply architecture uses a smaller, lower power 48 to 12V converter to distribute power throughout the vehicle with a load close to 12V. The simple power equation P = V? I and PLOSS = I2R can explain why 48V power distribution is more efficient than 12V.
For a given power level, compared with a 12V system, a 48V system has four times lower current and 16 times lower power consumption. At 1/4 of the current, cables and connectors may be smaller, lighter, and cost less. In addition, the distributed power architecture has significant thermal management and power system redundancy advantages (Figure 4).
Fig. 3 The efficiency of the standard DC-DC converter is 94% Fig. 4 The efficiency of the Vicor DC-DC converter is 98%
Modular component advantages of distributed architecture
The modular approach of distributed power supply (Figure 5) is highly scalable.
Figure 5 The modular approach of hybrid electric vehicles
The 48V output of the battery is allocated to various high-power loads in the car, which can maximize the advantages of lower current (4 times) and lower power consumption (16 times), resulting in a smaller and lighter PDN. According to the load power analysis of different distributed loads, a module can be designed and certified for appropriate power granularity and scalability for use in parallel arrays.
In this example, it is a 2kW module. As mentioned earlier, the granularity and scalability mainly depends on the system. By using distributed modules instead of large centralized DC-DC converters, N+1 redundancy can also be achieved at a significantly reduced cost. If the load power consumption changes during the car development stage, this method still has advantages. Engineers can add or remove modules without modifying the entire completed customized power supply. Another design advantage is to shorten the development time, because the module has been approved and certified.
Implement distributed modular 48V architecture in higher voltage battery systems
Figure 6 The modular approach of pure electric vehicles
Pure electric vehicles or high-performance hybrid vehicles can use high-voltage batteries because of the high power requirements of the powertrain and chassis systems. 48V SELV PDN still has significant advantages for OEM manufacturers, but now, power system designers have an additional challenge, that is, high-power 800V or 400V to 48V conversion.
In addition, this high-power DC-DC converter also requires isolation, but does not require voltage regulation. A big advantage of the decentralized 48V to 12V converter layout is better voltage regulation. The upstream high-power converter can use a fixed-ratio topology by using a regulated PoL converter. This has great advantages because the wide input to output voltage range of 16:1 or 8:1 is suitable for 800/48 and 400/48 respectively. Using a regulated converter in this range is not only inefficient, but also brings great problems to thermal management.
Due to the safety requirements of 400V or 800V power distribution, it is not only very difficult to disperse this high-voltage isolation converter, but also the cost is very high. However, high-power centralized fixed-ratio converters can be designed using power modules instead of large “silver box” DC-DC converters.
Power modules with appropriate granularity and scalability can be developed and then easily connected in parallel for a wide range of vehicles with different powertrain and chassis electrification requirements. In addition, Vicor’s fixed ratio bus converter (BCM®) is also bidirectional and supports various energy regeneration schemes. BCM adopts a sine amplitude converter (SAC™) high-frequency soft-switching topology, which can achieve an efficiency of more than 98%. They also have a power density of 2.6kW/in3, which can significantly reduce the size of centralized high-voltage converters.
Vicor is a supplier to the automotive market, providing the most advanced and innovative 48V solutions. The distributed modular approach of the automotive power supply architecture can simplify complex power supply challenges, thereby improving performance and productivity, and shortening time to market. Vicor is a leader in 48V power conversion and continues to innovate in power supply architecture, power conversion topologies, control systems and packaging.