“Manufacturers of cars, trucks, buses and motorcycles are rapidly adding electrification to their vehicles to improve the fuel efficiency of internal combustion engines and reduce CO2 emissions. Electrification options are plentiful, but most manufacturers opt for a 48V mild-hybrid system rather than a full hybrid powertrain. In the mild-hybrid system, a 48V battery is added in addition to the conventional 12V battery.

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By Patrick Wadden, Global Vice President, Automotive, Vicor, Nicolas Richard, Director, Automotive, Vicor

Manufacturers of cars, trucks, buses and motorcycles are rapidly adding electrification to their vehicles to improve the fuel efficiency of internal combustion engines and reduce CO2 emissions. Electrification options are plentiful, but most manufacturers opt for a 48V mild-hybrid system rather than a full hybrid powertrain. In the mild-hybrid system, a 48V battery is added in addition to the conventional 12V battery.

This quadruples the power capacity, which can be used for heavier loads such as air conditioners and catalytic converters. To enhance vehicle performance, the 48V system can power a hybrid engine that enables faster, smoother acceleration while saving fuel. The extra power also supports steering, braking and suspension systems, as well as new safety, entertainment and comfort features.

Figure 1: Traditional 12V centralized architecture (left) and 48V decentralized architecture (right).

The introduction of a 48V hybrid system has huge room for improvement. Overcoming the modification of the long-standing 12V power transmission network (PDN) may be the biggest challenge. Power changes often require extensive testing of new technologies, as well as new suppliers that can meet the automotive industry’s high safety and quality standards.

However, as the data center industry moves to 48V PDN, the benefits far outweigh the cost of switching. For the automotive industry, 48V hybrid powertrains offer a new way to quickly introduce new vehicles with lower emissions, longer range and lower fuel consumption. It also offers exciting new design options for higher performance and functionality while still reducing CO2 emissions.

Maximize PDN

Adding a 48V battery to power heavier powertrain and chassis system loads gives engineers options. Now, there are options to add systems that can handle 48V input directly, or convert 48V to 12V via a regulated DC/DC converter, preserving traditional 12V electromechanical loads (like pumps, fans, and motors). In response to changes and risks, existing mild-hybrid power transmission systems are slowly adding 48V loads, but still use large, centralized, high-power 48V to 12V converters that feed the 12V loads. However, this centralized architecture does not take full advantage of 48V PDN, nor does it take advantage of existing advanced converter topologies, control systems and packaging.

Figure 2: Standard DC/DC converters (left) are 94% efficient and Vicor DC/DC converters (right) are 98% efficient.

The vast majority of these centralized DC/DC converters are bulky because they use older low-frequency pulse-width modulation (PWM) switching topologies. For many critical powertrain systems, they are prone to single points of failure.

Another architecture is a decentralized power supply using modular power components. This power delivery architecture uses smaller, low-power 48-to-12V converters distributed throughout the near-load point of the vehicle near the 12V load.

Based on the fact that the higher the voltage, the lower the current, and the lower the wire losses, for a given power level, the current at 48V is 1/4 of the current in a 12V system, and the losses (I2R) are 16 times lower. At 1/4 the current, cables and connectors can be smaller, lighter and less expensive. Decentralized power architectures also offer significant thermal management and power system redundancy benefits (Figure 2). This is another way to spread kW-level power throughout a vehicle without the weight, heat and bulk of a traditional DC/DC converter.

Extensible Module

The modular approach to decentralized power delivery (Figure 3) is highly scalable.

Figure 3: Modular approach to hybrid vehicles.

The battery’s 48V output is distributed to various high power loads in the vehicle, maximizing the benefits of lower current (4x) and lower losses (16x), resulting in a smaller and lighter PDN. Based on power analysis of various distributed loads, a module can be designed and validated with appropriate power granularity, and can be used in parallel arrays to expand the power class of the system.

In this example, a 2kW module is shown, with granularity and scalability depending on the system. N+1 redundancy can also be achieved at a lower cost by using distributed modules instead of large centralized DC/DC converters. This method is also more convenient if the load power changes during the vehicle development phase. Instead of adding or modifying a grounded custom power supply, engineers can scale by adding or removing modules. Another design advantage is reduced development time because the module is already approved and certified.

Figure 4 shows the modular application areas in an all-electric vehicle.

Figure 4: Modular application of a decentralized 48V architecture in an all-electric vehicle.

For pure electric vehicles or high-performance hybrid vehicles, high-voltage batteries are used due to the high power demands of the powertrain and chassis systems. 48V SELV PDNs still have significant advantages for OEMs, but now power system designers are also faced with the challenge of converting large voltages of 800V or 400V to 48V.

This high power DC/DC converter also requires isolation but no regulation. By using regulated PoL converters, high power upstream converters can use fixed ratio topologies. This is very advantageous due to the wide input-to-output voltage range of 16:1 or 8:1 for the 800/48 and 400/48, respectively.

Using a regulated converter in this range is very inefficient and presents significant thermal management issues. OEMs often find this efficient step-down solution inside the battery pack and, in some cases, want to eliminate the battery. Vicor’s fixed-ratio high voltage conversion products provide fast current output with fast slew rates, allowing automotive OEMs to offload 12 to 14kg of unnecessary 48V batteries.

Separating such a high voltage isolated converter would be very difficult and costly due to safety requirements when distributing 400V or 800V. However, high power centralized fixed ratio converters can be designed using power modules instead of bulky silver box power DC/DC converters.

Power modules with the right level of granularity and scalability can be developed and then easily paralleled for a range of vehicles with different powertrain and chassis electrification requirements. Vicor Fixed Ratio Bus Converters (BCMs) are also bidirectional, supporting a variety of energy regeneration schemes. Due to the high frequency, soft switching topology of the sinusoidal amplitude converter (SAC), the efficiency of the BCM exceeds 98%. They also feature a power density of 2.6kW per square inch, which greatly reduces the size of centralized high-voltage converters.

A modular approach to automotive power systems simplifies complex power delivery challenges, improving performance, productivity and time-to-market.

Link to this article：48V Modular Power Architecture Addresses Automotive Electrification Challenges