What exactly is the 48V automotive system that we talk about every day?
Latest update time：2024-11-06
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In recent years, more and more automotive OEMs and Tier 1s have launched mild hybrid electric vehicles (MHEVs) and solutions with 12V/48V dual-battery vehicle system designs. Since Tesla’s high-profile announcement that Cybertruck and all future Tesla platforms will adopt 48V, it has added fuel to the 48V system, and the pace of 12V’s exit from the stage of history has accelerated.
Fu Bin｜Author
Automotive Development Circle | Produced
Part 1: Why 48V?
Today, 12V has too many limitations, and many automotive OEMs see 48V as the most reasonable development target because this voltage can achieve an ideal balance.
First, the power loss is lower, the efficiency is higher, and the energy utilization rate is improved, which is conducive to simplifying the heat dissipation design of automotive components and reducing costs. According to Ohm's law P=I²R, theoretically, in the 48V architecture, since the current is one-fourth of the 12V architecture, the various power losses caused by resistance in the power transmission system can be reduced to one-sixteenth of the original.
Second, the product/wiring harness is lighter, the cost is reduced, and it is conducive to reducing the weight of the entire vehicle and improving the battery life of the electric vehicle. According to the electric power formula P=V·I and PLOSS = I2R, doubling the voltage means that the device can obtain the same power with half the current, and reducing the current means that smaller wires, terminals and connectors can be used, all of which can reduce weight and reduce costs.
Third, 48V is far lower than the recognized limit of 60V required to prevent electric shock hazards. The maximum charging voltage of a 48V battery is 56V, which is very close to 60V, that is, the 48V battery voltage is the highest voltage level under safe voltage.
Fourth, the 48V power grid can also prepare the system for future applications in vehicle-to-everything (V2X) and ADAS (load point control).
The 48V system consists of three parts: BSG (engine belt-driven motor) + 48V battery + DC/DC. It is worth noting that the 48V mild hybrid system does not completely replace the traditional 12V electrical system, but retains the previous 12V system, which can maximize compatibility with the original system and save a lot of R&D costs. The 48V system has relatively stringent requirements on operating temperature and software matching calibration.
Part 2: 48V System Design Challenges
Since 48V is so versatile, why is it so difficult for the automotive industry to switch? In fact, this involves many design issues. At the same time, the 48V system has relatively stringent requirements on operating temperature and software matching calibration.
Arc protection
The risk of arcing is affected by the voltage level and the distance between terminals, and the temperature can reach 2800-19000°C. In a 12V circuit, the arc will generally extinguish quickly, but at 48V, the arc may continue and damage the terminals and connectors.
It is not certain whether 12V blade fuses for 48V systems can provide adequate arc protection. Also, since the relay contact distance required for 48V systems will be greater than that required for 12V systems, fuses and relays will need to be redesigned. Since the requirements of these components can be easily met by using semiconductor devices, these problems are likely to be solved by electronic solutions. In other words, more eFuse solutions will be adopted.
Voltage
Architectures are constantly changing
It is currently difficult to make the leap to a full 48V system, so most solutions on the market do not completely replace the traditional 12V electrical system, but retain the previous 12V system. This allows for maximum compatibility with the original system and saves a lot of R&D costs. Therefore, it is very likely that the equipment will have both a 12V system and a 48V system. Therefore, the entire power architecture may be different in each period in the future.
EMI requirements are higher
At 48V, although the output power is the same, the lower load current reduces the conducted (differential) emission, so the switching waveform (the second major source of EMI) becomes the focus. Larger switching waveform amplitudes increase EMI, and noise radiation from the switch node is also aggravated by large copper areas (such as inductors), especially at 48V input voltage.
Therefore, when selecting a power regulator for a 48V application, it is important to evaluate the impact of high input voltage on EMI and select a regulator with EMI mitigation features to reduce the additional noise. Even when using a low-noise regulator, it is still necessary to follow low-noise PCB layout principles, select appropriate EMC components, and design in a systematic way. The best step in designing a low-noise power converter is to first simulate it with reference to the datasheet and evaluation board examples.
LM5164-Q1 EMI performance with 24V and 48V inputs under the same load conditions. Source: TI
BMS control is more cautious
The 48V battery system consists of lithium-ion cells, which require more attention and handling than lead-acid batteries. For this reason, 48V cars require a battery management system (BMS) responsible for monitoring the battery voltage and battery temperature so that the battery can be charged safely. This situation is also further complicated by the fact that the 48V system has regeneration capabilities. When the remaining charge in the car battery is low enough, regeneration can be commanded, but the control of the BMS needs to be very careful, which is crucial to prevent overcharging or overheating.
Terminal contact and locking
Avoid using terminals with intermittent contact or micro-corrosion, otherwise micro-arcing will occur, damaging the terminal material and increasing resistance. Use effective terminal secondary locking to prevent intermittent power outages and arc formation caused by terminal withdrawal (TPO). Before repairing the 48V connector, be sure to turn off the power to avoid high-temperature arcing when disconnecting.
Creepage distance and clearance
Creepage distance is the shortest distance along the surface of an insulating material, and clearance is the shortest distance in the air between conductors. Use the IEC 60664-1 specification to determine creepage distance and clearance. Most traditional automotive connectors meet the clearance requirements, but some require design adjustments to meet creepage distance.
Creepage distance and electrical clearance, source: APTIV
Voltage Isolation
In a mixed voltage system, current must be prevented from flowing from 48V to 12V, so the best way is to isolate circuits of different voltages or physically partition them within the connector. Also, when wiring, try to separate 48V and 12V circuits and provide additional protection for 48V wires in vulnerable locations. Avoid using the same grounding stud to prevent current from flowing across voltages through shared connections.
Sealing requirements
When the 48V connector accidentally comes into contact with electrolytes such as salt water, the electrochemical corrosion reaction produced will cause more serious corrosion to the terminals than in the 12V case, so the seal must be kept tight enough.
The supporting industrial chain needs to be replaced
After increasing from 12V to 48V, the voltage resistance of components, connectors, switches, etc. needs to be improved; in order to be compatible with 12V hardware, a 48V to 12V DC transformer is also required; due to the increase in voltage, the contacts are more likely to produce arcs, so electronic relays are usually used to replace traditional electromagnetic relays or electronic fuses; even for safety reasons, 48V connectors are usually color-coded in light blue to remind people to wear personal protective equipment.
Part 3: Changes in 48V Design Architecture
Tesla is a staunch "48V enthusiast". Tesla not only stated that its CyberTruck adopts a full 48V solution, but also will make a series of design modifications, stop using the 12V bus in several existing models, and has formed its own "secret" accessory team to develop products specifically for the 48V architecture, such as lighting, winches and air compressors.
However, after disassembly and analysis, it was found that CyberTruck designed the 48V connector and packaging in blue, which is better distinguished from the high-voltage orange. At the same time, the current design of CyberTruck is somewhat different from what Tesla said. Not all low-voltage designs use 48V, and the 12V design is still retained.
Therefore, there is no real full 48V automotive system in the market at present, but only a gradual transition to a 48V system, and it is expected that many vehicles will continue to use existing 12V accessories and subsystems for 10 to 15 years.
At present, a simplified diagram of the more commonly used 48V electrical system is shown in the figure below. It consists of two power buses, a 12V battery and bus for powering most traditional automotive loads; a 48V battery and bus for powering electric drive motors and other high-power accessories. The 12V system runs all conventional equipment, including infotainment systems, lighting, and body electrical accessories such as windows, doors, seats, etc. The 48V system runs the electric drive motor and any heavy loads such as HVAC, selected pumps, steering and suspension systems, and if the ICE uses an electric turbocharger, an electric turbocharger is used.
The two main electrical systems are connected to a bidirectional buck-boost DC/DC converter that services the 12V and 48V buses, and an inverter to operate the three-phase synchronous induction drive motor. Some S/Gs are belt-driven, while other manufacturers place the S/G between the engine and transmission.
There are also some more practical approaches to implement a distributed power delivery architecture, such as the distributed system developed by Vicor. In this system, the vehicle's 48V power comes from the main 400/800V battery and is then sent to a 12V power converter close to the load point. By using two or more independent, isolated voltage converters to supply power, redundant power can be provided for braking, steering and other ASIL D safety-critical functions.
In addition, Vicor has also demonstrated a very forward-looking solution. Currently, the transition of automotive E/E architecture from domain control Domian to regional control Zonal is the mainstream, and Vicor combines 48V and Zonal together.
From the figure below, it can be seen that the vehicle contains 12V and 48V loads, the low-voltage load is transmitted through 48V, and the 12V electrical load is converted through 48V. The regional E/E architecture is equipped with a high-performance computing unit and connected through the CAN bus and automotive Ethernet to achieve more efficient load management and power distribution. The 48V PDN solves the incompatibility problem between 400V/800V charging infrastructure by integrating the charger and 48V power delivery network into the battery pack. This integration not only reduces heat, cost and weight, but also improves the overall efficiency of the system.
Last words
Currently, the application of 48V technology is still relatively limited. 48V systems have been available for a few years, mainly to power the starter-generator and high-power accessories (such as active suspension and power steering) of mild hybrid vehicles. As Tesla explained in the presentation, the higher the voltage, the lower the current, and the thinner the wires are needed, which reduces weight and saves costs.
引入48V轻度混合动力系统后，设计完成的优势显著。然而，改变传统12V供电网络（PDN）的犹豫依然存在，因为转换过程可能涉及大量测试，还可能需要符合汽车产业高安全性和高质量标准的新供应商。数据中心行业在转向48V PDN的过程中发现，这一变革的优势远远超过了转换成本。同样，对于汽车行业而言，48V轻度混合动力系统为快速推出排放更低、油耗更低、行驶里程更远的全新车辆提供了新途径。此外，它为提升性能并减少二氧化碳排放带来了全新设计选择。
So, can 48V motor drive completely replace 12V motor drive? The answer is no. TI's Karl-Heinz Steinmetz once told EEWorld that it may take 10 to 15 years for high-end automakers to fully switch to 48V system, and the 12V/48V dual power structure will continue to exist for some time in the future.
References
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