There are many electrification choices, but most manufacturers are opting for a 48-V mild-hybrid system rather than a full-hybrid powertrain.
E-mobility is perhaps one of the most significant challenges that technology companies and consumers have had to face in recent years. While there is an increasing need to find eco-friendly systems that can revolutionize the way we move, there is also a need to ensure that the new green technologies are as efficient and effective as possible in price/performance terms.
Automotive OEMs are challenged to meet increasingly stringent CO2 emission standards while enhancing vehicle performance to remain competitive. They are addressing the challenge by deploying electrification, not just for the various types of electric and hybrid-electric vehicles but also to make vehicles based on internal combustion engines (ICEs) greener and more efficient. As higher-voltage batteries, from 48 V to 400 V and 800 V, have been adopted to meet the new power requirements, power delivery architectures have risen in complexity and new size and efficiency requirements have emerged.
Mild-HEV (MHEV), or light-hybrid propulsion, systems are the gateway to electrification and are expected to contribute to the exponential growth of hybrid models. The MHEV system is capable of recovering vehicle energy during braking and provides energy during the restart of the vehicle, thus reducing gas consumption and CO2 emissions.
A second electrification approach for HEV models involves an electric motor working together with the ICE, enabling the vehicle to travel in fully electric mode for a few kilometers. Another popular alternative is the plug-in hybrid-electric vehicle (PHEV), in which the battery can be recharged by the grid, and the range at zero emissions increases to about 50 km. The level of electrification is decidedly higher in this case than in MHEV and hybrid technologies — as are the purchase costs. Dozens of PHEV models are coming onto the market.
Battery electric vehicles (BEVs) lack an ICE and are instead powered by the combination of inverter plus electric motor. BEVs are rechargeable through the grid and during regeneration while braking. Extended-range electric vehicles (EREVs), meanwhile, have a small internal-combustion engine that’s used exclusively as a current generator to recharge the batteries when the level is low. Finally, there are fuel-cell electric vehicles (FCEVs), which are powered by hydrogen cells.
Figure 1 presents global forecasts by powertrain type. The solutions to today’s e-mobility challenges could be not only in new energy storage technologies, such as solid-state batteries or hydrogen fuel cells, but also in improved car efficiency through weight reduction and new electrical architectures.
“Today’s challenges with electrification are keeping costs down; meeting aggressive CO2 emission targets; managing change in power requirements; powering legacy 12-V loads; delivering lighter, higher-performing vehicles; increasing power levels; achieving faster charging times; and managing higher voltages from 800- and 400-V battery systems,” said Patrick Wadden, global vice president of automotive business development at Vicor.
Manufacturers of cars, trucks, buses, and motorcycles are rapidly electrifying their vehicles to increase the fuel efficiency and reduce the CO2 emissions of internal-combustion engines. There are many electrification choices, but most manufacturers are opting for a 48-V mild-hybrid system rather than a full-hybrid powertrain. In the mild-hybrid system, a 48-V battery is added alongside the traditional 12-V battery.
“There is either an 800- or a 400-V battery in the vehicle. Vicor takes 800 or 400 V from the battery and converts the power to 48 V for powering loads such as the electric turbo, head-up windshield [display], and cooling pumps,” said Wadden. “Systems that are powered from the 800- or 400-V battery have the option of completely eliminating the 48-V battery and creating a virtual 48-V battery [Figure 2]. This approach offers the OEM a higher power density and reduced weight and size, all enabling an extended vehicle range. These solutions are scalable and therefore address entry-level to luxury vehicles.”
Efficient power distribution
The 48-V technology increases power capability by 4 × (P = V • I), which can be used at startup for heavier loads, such as the air conditioner and catalytic converter. To increase vehicle performance, the 48-V system can power a hybrid motor that is used for faster, smoother acceleration while saving fuel.
“Overcoming the hesitancy to modify the longstanding cost-optimized 12-V power delivery network [PDN] may be the biggest challenge,” said Wadden. “For the automotive industry, a 48-V mild-hybrid system provides a way to rapidly introduce new vehicles with lower emissions, longer range, and higher gas mileage, and [is] a practical approach. It also delivers new and exciting design options for higher performance and features while still reducing CO2 emissions [Figure 3].”
The vast majority of DC/DC converters used in automotive are based on old, low-frequency, pulse-width modulated (PWM) switching topologies and thus are bulky and heavy. Decentralized power delivery using power modules is a more up-to-date alternative.
Figure 4 presents a diagram of a centralized system versus a decentralized system. On the left is a traditional 3-kW silver box, traditionally with a 400-V input to a 12-V output powering 12-V loads in the car. On the right is an example of how 48 V is used around the car: The converter is placed right at the point-of-load, the decentralized model does away with the big silver box and spreads the power distribution as needed around the vehicle. “This also allows for implementation of ASIL FUSA [Automotive Safety Integrity Level Functional Safety] with redundant supplies,” said Wadden. “As the power requirements go up, it becomes more and more difficult to manage [a centralized system], and to keep adding these older, traditional silver boxes isn’t an option.”
This power delivery architecture uses smaller, lower-power 48-V to 12-V converters. The decentralized power architecture offers significant thermal management benefits in a power supply system.
“The benefits to using a decentralized model can be realized even more at the system level, with lighter-weight cabling around the vehicle,” said Wadden. “There are some nice benefits to placing the converter close to the load in terms of minimizing impedance and resistance. Some of the cooling methods can be simplified , and in some cases the designer can eliminate a cold plate or liquid cooling. The option to implement functional safety with more options and flexibility comes into play [Figure 5].”
New 48-V PDNs must support legacy 12-V loads with increased power requirements and new high-power drive, steering, and braking systems using cables. Delivering more 48-V power with an increasing number of loads requires high-density modules. Vicor offers several modules for power delivery from 48 V, including fixed-ratio and regulated conversion solutions that support both 48-V and 12-V loads in buck or boost mode. The converters can be contained in a single housing or distributed throughout the vehicle using a smaller and lighter 48-V PDN.
The Vicor NBM is used in a decentralized architecture whenever OEMs need to place voltage-conversion stages around the vehicle close to the load and either step 48 V down to 12 V or boost 12 V to 48 V.
With the use of 400-V and 800-V charging stations, the compatibility of the vehicle with any station requires a conversion solution that is as simple as possible but also, above all, efficient. The NBM6123 provides 6.4-kW, fixed-ratio 400-V and 800-V conversion in a 61 × 23-mm CM-ChiP package, enabling a scalable, high-efficiency, high-density solution for compatibility between roadside charging stations and vehicles. The bidirectional capability of Vicor solutions allows the same module to be used for step-up or step-down conversion. The NBM6123 can also be used for power delivery to the vehicle for air conditioning during charging, minimizing the battery-balancing circuit.
The move toward vehicle electrification is taking many forms today, and powering them is complicated. A decentralized, modular power approach is inherently more flexible and scalable than traditional, centralized systems. Vicor’s high-performance solutions are small and lightweight, and are designed to address power conversion, charging, and delivery for any system.
This article was first published on EE Times EuropeRelated articles: