Utilize the high-voltage battery of electric vehicles to provide 12V voltage more effectively. The author of this article is Nicolas Richard, Vicor European Automotive Business Development Director.
Yes, automotive 12V lead-acid batteries are about to withdraw from the market. Europe has issued a decree that after 2030, all new cars will no longer use lead-acid batteries, which poses a great challenge for OEMs to find alternative solutions. Although this may seem like a daunting task, it can also bring huge opportunities to not only eliminate batteries that are harmful to the environment, but also to reduce vehicle weight and improve overall efficiency.
The 12V battery and power supply network (PDN) is a global standard that supports hundreds of loads, including some loads that are closely related to safety. Therefore, the solution must be innovative and robust. The high-density, high-power, and high-efficiency power modules used to connect high-voltage, 48V and 12V PDNs can provide solutions with the highest flexibility and scalability for this upcoming challenge.
When considering potential solutions, OEMs must consider several important factors: increase power to support new features with better performance, increase efficiency to extend driving range and optimize thermal management, reduce carbon dioxide, optimize cable routing, reduce wire harness weight, and Meet EMI requirements. These are some of the variables in this complex equation.
There are two main options for solving this equation. Replacing the 12V lead-acid battery with a 12V lithium ion battery is an option. Although it does slightly reduce weight, it will retain the decades-old tradition of 12V PDN and will not produce other advantages. Another option is to support 12V PDN powered by 400V or 800V main battery in electric vehicles and hybrid/plug-in hybrid vehicles. The latter option has many advantages, but both options are worthy of further exploration.
Use 12V lithium ion battery
Simply replacing the 12V lead-acid battery with a 12V lithium ion battery can indeed save about 55% of the weight, but it has a high cost impact. A 12V lithium-ion battery requires a battery management system (BMS) to control charging and keep the battery fully operational during the entire life cycle of the car. This is how Tesla and Hyundai are developing.
In addition, a large DC-DC converter (with voltage and current regulation characteristics) from high voltage to 12V is needed to charge the 12V lithium-ion battery and power the electrical load. But this will not add any advantage. What it adds is only the weight, the complexity of the overall layout of the vehicle, and the system cost, and it will also reduce the overall reliability of the vehicle. In contrast, eliminating the 12V battery can not only reduce the weight of the car by 13kg, but also increase the cargo space by 2.4%.
Traditional 12V PDN is inefficient
Maintaining a 12V physical battery means maintaining an inefficient PDN with unnecessary redundancy. In a typical automotive 12V PDN, all 12V loads connected to the 12V bus have an internal pre-regulator that can convert a wide input voltage range (usually from 6V to 16V) to 5V, 3.3V or lower. From a global system perspective, whether it is an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle, there is a series regulator redundancy. A DC-DC converter from high voltage to 12V can stabilize the 12V bus (high efficiency), and the pre-regulator can provide the appropriate internal voltage for each load (Figure 1).
This traditional architecture originated in the era when cars were equipped with alternators. The alternator is a sensitive 12V PDN that requires voltage regulation to charge the battery, keep the radio working during a start-up event, or keep the car’s incandescent headlights properly brightness. OEM manufacturers have creatively bypassed the 12V power limitation. In recent years, they have designed two 12V batteries, a 24V battery for power steering, and several DC-DC converters in between.
Figure 1: Typical E/E used by xEV, using a 12V battery with a redundant voltage regulator. The high voltage to 12V DC-DC can stabilize the 12V output and charge the 12V battery. Each 12V load in the vehicle has a pre-regulator to provide the proper voltage required for the load to work.
Replace the 12V battery with a dummy battery
A better way to solve this problem is to completely reconsider the automotive PDN: abolish the 12V physical battery and replace it with the 12V “virtual” battery in the main battery of the electric vehicle (Figure 2). Every electric car has a main battery, so it is meaningless to carry additional energy storage devices. The ideal vehicle architecture is to use a high-voltage battery to power the power system and all auxiliary loads. Vicor high-density bus converter module technology can realize this scheme, it virtualizes the low-voltage battery (48 or 12V) directly from the high-voltage battery (400 or 800V).
Figure 2: The optimized E/E architecture can eliminate the 12V physical battery. Use Vicor BCM bus converter technology to convert high voltage batteries to create virtual 12V batteries.
Vicor BCM® bus converter adopts zero voltage, zero current switching (ZVS/ZCS) technology, and its operating frequency is higher than that of conventional converters, so its response speed is faster than that of physical batteries. For example, the BCM6135 is different from the conventional ZVS/ZCS resonant converter. The operating frequency is 1.2MHz. The BCM operates at a narrowband frequency (Figure 3). The high frequency operation of BCM can provide fast response to changes in load current and a low impedance path from input to output. The combination of fixed ratio conversion, bidirectional operation, fast transient response (more than 8MA per second) and low impedance path can help BCM make the high voltage battery look like a 48V battery, which we call “transformation.” Compared with conventional converters, this function of transforming the power supply is not only an important advantage, but also an important differentiation feature.
Figure 3: The fast load transient response of BCM6135 is the key to supporting 12V loads. The transient response is 8 million amperes per second (8MA/s). Yellow: input voltage (800VDC), red: output voltage (48V), blue: output current.
Figure 4: The functional block diagram of the BCM bus converter. Although BCM can perform DC-DC conversion, it can also use a transformer to perform high-efficiency AC-AC conversion. Not only can the size be scaled by the K factor, but also the switch module can be used to convert between AC and DC. The switch is completed at a high frequency, and because it has the same energy transfer characteristics as a transformer, the conversion can not only respond quickly to transient load changes, but also provide a low impedance path between input and output.
Vicor BCM can be used as a fixed ratio converter, where the output voltage is a fixed ratio of the input voltage. The Vicor BCM6135 converter is isolated and uses a 61 x 35 x 7 mm package to provide 2.5kW of power with a peak efficiency of over 97%. It can be easily connected in parallel in the array to provide more power.
The fixed ratio property of this BCM ensures that the virtual battery remains within its proper operating range. For example, in an electric car powered by an 800V battery, the high-voltage battery can be guaranteed between 520 and 920V. The BCM6135 with a ratio of 1/16 can virtualize a 48V battery, ensuring that the voltage range is between 32.5 and 57.5V. The ratio of BCM6135 1/8 can be used for 400V electric vehicles (Figure 3).
Battery virtualization can also be extended to a 12V bus using a 1/4 fixed-ratio converter. In this case, galvanic isolation is not required, and Vicor NBM™ bus converters can be used. Like the other characteristics of BCM, the NBM non-isolated bus converter has all the advantages mentioned above: fast transient response, low impedance and bidirectional operation. The voltage range of the 12V bus is kept between 8.125V and 14.375V, and the ratio to the high-voltage battery voltage is fixed. BCM and NBM technologies are ideal transformers to connect the power supply networks of automobiles.
Table 1: The minimum and maximum voltages on the 48V bus and 12V bus using Vicor BCM/NBM bus converter technology. Both the 48V and 12V voltage ranges comply with the VDA 320 and LV 124 standards.
Figure 5: 12V and 48V battery virtualized E/E architecture based on BCM6135 and NBM2317 modules. The 48V bus can also be used as a more efficient power source to power higher loads in the vehicle, such as air conditioning condensers, water pumps, and active chassis stabilization systems.
It is essential to ensure the power supply redundancy for functionally safe loads. The Vicor power module is fully expandable in terms of power supply and transmission, so it can be designed as a redundant PDN, so that it can supply power to the load that is critical to functional safety through two dedicated power conversion paths. Ultimately, OEM manufacturers can implement localized energy storage to ensure the safe operation of important systems such as ADAS, steering and braking.
Where will the electric vehicle power supply network go?
12V lead-acid batteries will soon withdraw from the European market. Given that all innovations have driven the redesign of the electric vehicle power supply network, this timing is very appropriate.
Automotive electrical PDN is at the crossroads of 12V power supply. While trying to keep the architecture changes to a minimum, more and more stringent power loads are applied to vehicles. Tesla CEO Elon Musk said: “Why do we still use 12V? 12V is just a residual voltage, which is indeed too low.”
OEM manufacturers are scrambling to design better PDNs to provide electric vehicles with greater mileage and higher performance. The complete elimination of the 12V battery is obviously a long-term solution, which not only reduces weight and space, but also provides better transient response and system performance. Vicor technology not only realizes these advantages, but also provides unparalleled flexibility, scalability and power density. Vicor’s PDN module solution provides an ideal building block for solving the recent challenges of the new generation of xEV’s 12V power supply network.
Nicolas Richard, Director of European Automotive Business Development , Vicor
Before joining Vicor, Nicolas served as the head of the North American automotive business department at IDT (Renesas Electronics), where he was mainly engaged in the technical sales of power systems, infotainment systems and ADAS systems. Before joining IDT, he served as a field application engineer at ON Semiconductor for 4 years, leading an internal design and application team (a “concept to product champion” team), responsible for ON Semiconductor’s automotive sales in Detroit, Michigan New product growth strategy. His work experience also includes 9 years of engineering and development work at Continental Motors. During this period, he held various engineering design positions in Continental’s Hybrid and Electric Vehicles department, mainly designing DC/DC converters and traction inverters. Changer.
This article was originally published by Power Electronic Europe.
