48V Vehicle Electrical System – More Than Just a Bridging Technology?

Article By : Dusan Graovac, Christoph Schulz-Linkholt, Thomas Blasius

High-performance semiconductors enable efficient and reliable solutions for a wide range of automotive 48V applications...

In recent years, the development of the 48V vehicle electrical system has focused primarily on P0 and P1 configurations in the powertrain of mild hybrid vehicles. The motivation for this was the cost advantage compared to purely electric or plug-in hybrid vehicles, the lower development effort and the immediate CO2 reduction potential for the vehicle fleet. For many manufacturers, the introduction of these mild hybrid vehicles was the quickest and most cost-effective solution to achieve current limit values for the vehicle fleet. For this reason, the 48V vehicle electrical system is often regarded as bridging technology until a sufficiently large HV (high-voltage) BEV (battery-powered electric vehicles) fleet has established itself worldwide to comply with the CO2 regulations. However, 48V technology offers far more potential than just bridging the gap to pure BEV vehicles.

To comply with the CO2 specifications, the 48V technology enables regenerative braking, intermediate energy storage and subsequent electrical support of the conventional combustion engine. Future limit values, however, do not seem to be reproducible with this concept. This is why many automotive manufacturers are turning towards HV-BEVs. Figure 1 schematically illustrates how the market share of electric vehicles would have to develop in order to comply with future limit values. This explains why the 48V vehicle electrical system is often regarded only as bridging technology.

Fig. 1: Schematic diagram of how the market share of ICE, 48V mild hybrid and electric vehicles would have to develop in order to meet future limit values.

The purely electric car with zero local emissions is clearly the ideal solution from a technical point of view and must therefore be developed and promoted accordingly. However, to rely solely on HV electromobility is a controversial matter of debate. There is a risk that the development of promising alternative concepts such as fuel cells or CO2-neutral synthetic fuels will be undermined, thereby losing potential key technologies. In addition, the global switch to a purely electric vehicle fleet in terms of raw material production and energy generation cannot yet be presented as CO2 neutral. In particular, the energy mix and the consideration of the production and recycling of HV batteries can have a negative influence on the carbon footprint. The decisive factor will be the time scale on which electromobility can be implemented for a CO2-neutral future and how the 48V vehicle electrical system can support this. The following therefore focuses on the question of whether the 48V vehicle electrical system will only be a bridging technology in vehicles and whether there will be further potential for the 48V vehicle electrical system.

48V Architectures and Applications

There are various integration options (P0 to P5) for the electrical machine (EM) in the powertrain. The basic functions ‘boost’ and ‘energy recovery’ with connected as well as ‘coasting’ with disconnected combustion engine can be realised in all configurations, whereby an automated starting clutch is necessary for disconnected operation. What the P2 to P5 configurations have in common – unlike the P0 and P1 configurations coupled to the crankshaft speed – is that they allow braking energy to be recuperated when the internal combustion engine is disconnected and enable purely electric driving within the performance range of a 48V system. The P4 and P5 architectures also allow an all-wheel drive function on a 48V basis.

Regardless of whether the drive is a HV-BEV, fuel cell or synthetic fuel, the 48V voltage level in additional units enables energy savings compared to 12V and simplifications for installation and operation in the vehicle compared to HV – and thus a corresponding potential for optimisation. Depending on the drive concept, potential 48V applications are shown here as illustrated in Fig. 2 e.g. eTurbo (electric turbocharger) with 2 – 4 kW, eA/C (electric air-conditioning compressor) with 4 – 5 kW, electric heaters such as eCAT (electric catalyst heating), PTC auxiliary heaters or windscreen de-icing with 1 – 5 kW, ERC (electric drive and roll stabilisation) with 1 – 5 kW, pumps and fans up to 1 kW and other applications with high power density and/or continuous use. The development of these applications in the direction of 48V can currently be seen in second-generation mild hybrid vehicles with P2-P4 configurations and also as a third voltage level in the HV-BEV.

Fig. 2: Schematic illustration of a dual-voltage vehicle electrical system with 48V auxiliary units.

If we look a little further into the future at the business segment of urban mobility or what is known as “Mobility as a Service (MaaS)” as an overall concept, this opens up further applications for 48V technology. In contrast to today’s requirements for the HV-BEV with regard to a very long range (> 400 km) with ever shorter charging times, the main focus here is on cost, battery weight, insulation protection and short driving distances from 2 km to 20 km. There is sufficient time for charging during working hours, overnight or similar depending on the infrastructure and parking of the vehicle. For this requirement, there are calculations that a 30 kW drive is sufficient to complete the urban and overland standard cycle with small city cars. In addition, a 48V BEV powertrain is approximately 25% cheaper than a HV 400V BEV powertrain in this operating cycle. Furthermore, there are already commercial vehicles with a payload of up to 1,000 kg based on a 48V BEV. Motorcycles and electric scooters as 48V BEV are also establishing themselves in the market, in some cases even with replaceable batteries. All these implementations can use applications already developed or to be developed for the mild hybrid car, e.g. battery with battery management system (BMS), inverters, DC/DC converters and auxiliaries.

The question remains as to how the topic of “MaaS” will continue to develop. Here, even traditional car manufacturers are currently repositioning themselves and developing strategies on how to implement the transformation to a MaaS provider and thus define a completely new ecosystem. In these models the complete range of mobility is addressed and apart from the small urban vehicles for a few persons there is also a “shuttle POD” similar to EasyMile with up to 12 persons transport capacity, “people mover” similar to buses and “cargo mover” for the last mile service. Due to the greater weight compared to the small city car, higher power densities are required here. This could lead to the use of 48V not only for the traditional powertrain and auxiliary units, but also for steering, braking, driving stabilisation and possibly also for the wheel hub motor. Similar applications can be found in the truck, agricultural, construction machinery, forklift, special vehicle and aviation markets.

Even if only some of the above-mentioned applications, some of which are still far in the future, are implemented, this would significantly extend the 48V lifecycle.

High-Performance Semiconductors for the 48V Architecture

Semiconductors in the 48V vehicle electrical system are used in particular for controlling electric motors and in the inverter for power distribution or for supplying the auxiliary units. They also provide the connection between the 48V and 12V electrical system levels by means of DC/DC converters. Corresponding components are sensors, microcontrollers, power, supply, communication and driver ICs.

The block diagram (Figure 3) shows the basic layout of the semiconductors used to control a starter-alternator – the key component in the 48V vehicle electrical system. To power the microcontroller, the system voltage (48 V) is reduced to a level common for microcontrollers and other ICs. This is the essential function of the supply IC (safety system supply). It also performs additional tasks in the area of functional safety. The microcontroller enables both field-oriented control of the electric motor and control of the exciter winding in alternator operation. For this purpose, complex timer units are implemented in the microcontroller. In addition, it communicates with other control units of the vehicle via various communication buses (e.g. via CAN). With appropriate sensors, the rotor position and rotational speed of the electric motor rotor and the currents currently flowing in the inverter are measured and transmitted to the microcontroller. Smart sensor ICs can already process the measured data internally and make this data available to the microcontroller as digital values via a sensor bus. For precise motor control, it is also necessary to transmit the currents in the individual motor phases to the microcontroller. For this purpose, either shunt resistors are used in the inverter or the currents are determined using magnetic field sensors.

Fig. 3: Block diagram for a 48 V micro hybrid system with the main semiconductor components.

Low-loss MOSFETs are often used as power stage ICs in the 48V vehicle electrical system, which are usually controlled and monitored by dedicated 3-phase drivers and switched to a safe state in an emergency. Other important components, in addition to the motor driver ICs, are high-performance gate driver ICs which, in conjunction with MOSFETs, provide highly reliable battery switches or safety switches for 48 V/12V isolation. The 48V vehicle electrical system is electrically coupled to the 12V vehicle electrical system using a DC/DC converter.

Complete 48V Portfolio

Infineon offers a complete system of chipset solutions – from voltage regulators, transceivers and sensors to microcontrollers, smart power drivers and very low-resistance MOSFETs – for 48V systems.

The AURIX microcontroller family was initially very successful, especially in the area of powertrains, but also addresses other domains such as safety/security or driver assistance systems. In the meantime, the products of the latest AURIX generation TC3xx (40 nm with embedded flash) are in production and offer all the ingredients for high-performance and efficient designs. This allows designers to choose from a broad portfolio of scalable memory sizes, peripheral functions, frequencies, temperature and package options. The multicore architecture of the AURIX TC3xx family contains up to six independently operating 32-bit TriCore processor cores and thus significantly boosts computing performance compared to the previous generation. TC3xx microcontrollers offer the ideal combination of real-time capability, data security and functional safety for ISO 26262 system requirements up to ASIL-D.

Other important communication and power components for 48V systems are isolated CAN transceivers and bridge driver ICs (e.g. TLE9180).

48V applications are experiencing high demand for 80V and 100V MOSFETs for applications such as starter-alternators (belt-driven or integrated), DC/DC converters or battery main switches. Infineon’s OptiMOS5 family offers a broad portfolio of low, scalable on-state resistors (down to 1.2 mW) and various packages such as the new TOLL (TO-leadless), TOLG (HSOG-8), TOLT (top-side cooling for high performance), bare die and chip embedding.

48V systems also require precise and robust sensors for sensing the rotor position of BLDC motors as well as for current measurement. Basically, the sensors should take up as little space as possible, have low losses, be flexible and cost-effective and be highly precise, robust and safe in operation over the entire service life. By way of example, the Hall-based current sensor XENSIVTM TLI4971, the first member of Infineon’s new “coreless” current sensor family, meets all these requirements. It measures currents up to 120 A and is supplied fully calibrated.

Chip Embedding

Infineon Technologies has partnered with Schweizer Electronic AG (https://www.schweizer.ag/en/home.html ) to develop power MOSFET chip embedding technology (Fig. 4). The technology can increases the performance of 48V systems up to 60% while reducing complexity in assembly and joining technology. In chip embedding, the MOSFETs are not soldered onto printed circuit boards as before, but integrated directly into them as so-called standard cell (MOSFET bare die in a copper leadframe). The thermal and electrical advantages associated with this enable significantly higher power density. At the same time, reliability can be increased, specifically in comparison to ceramic modules. This allows developers to either increase the performance of a 48V system or make it more cost-effective. For example, integrated 48V starter-alternators make a major contribution to the fact that mild hybrid vehicles emit up to around 15% less CO₂ than conventional powertrains.

Fig. 4: With chip embedding, the power density can be increased by a further 35%.

Conclusion

Against the background presented here and the application examples mentioned, it certainly makes sense to make further investments and system optimisations for the automotive use of a 48V vehicle electrical system voltage. Infineon is therefore pursuing a consistent strategy of investing not only significantly in high-voltage technologies for electric vehicles, but also in 48V technologies and products. To implement this, a broad, scalable portfolio of high-performance semiconductors is available.

— Dr.-Ing. Dusan Graovac, Director and Global Head of Automotive System Engineering Infineon Technologies
— Christoph Schulz-Linkholt, Principal System Architect Power Distribution Infineon Technologies
— Dr. rer. nat. Thomas Blasius, Automotive System Marketing Body Infineon Technologies

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