Fewer emissions, greater driving pleasure: the 48-volt wiring system is the solution.
Fewer emissions, greater driving pleasure: the 48-volt wiring system is the solution.
( Bild: Avnet Silica)

vehicle electronics The advantages of 48-volt vehicle electronics

| Author / Editor: Gregor Knappik * / Jochen Schwab

In 1879 Karl Benz received a patent for a combustion engine. The "horseless car" continuously developed into a modern car. With the introduction of the 48 V wiring system, the next evolutionary step is imminent. An overview.

Over the last 20 years, the development process has accelerated as the internal combustion engine has faced competition from the introduction of electric motors, which are used in hybrid and increasingly also in pure electric vehicles (EVs). Over the next ten years, the situation will become even worse as personal mobility undergoes a radical rethink. The result will be a completely new conception of vehicle architectures - including their subsystems, their control algorithms and their fundamental fundamentals, such as the operating voltage of their electrical systems.

Driver for changes: The climate and more driving fun

Why the increasing pressure to change? An immensely important factor is the great challenge of reducing the impact of mobility on the climate. Legislators are introducing strict new regulations for vehicle emissions. Norway, for example, says that all new cars should be emission-free by 2025. The Netherlands wants half of all cars sold in 2025 to be electric. Denmark wants to stop selling cars with internal combustion engines by 2030. By the same date, India wants all cars to be battery-powered and China also plans to stop selling cars with an internal combustion engine. Meanwhile, both the EU and the US are tightening their emission standards.

The second driving force for change is that today we demand significantly more from our vehicles and that it makes sense to fulfill this wish with electrical energy. What used to be a dashboard with a mechanical speedometer and rev counter is now an app-enabled multimedia infotainment system connected to the Internet. What used to be a mechanical distributor and carburetor is now a sophisticated multi-sensor and multi-actuator engine control unit. And where parking sensors used to be reserved only for the upper equipment lines of certain vehicle models, today an increasing number of advanced driver assistance systems such as tracking, adaptive speed control, emergency braking, blind-spot monitoring, and many other functions are being used in more and more vehicle classes.

In addition to these comfort features, car owners also want their vehicles to be more fun to drive. This, in turn, leads to the introduction of electric power steering, electronically controlled automatic transmissions, active roll stabilization, electric turbocharging and even electric traction support. All this adds up to a not inconsiderable amount of electrical energy flowing in the vehicle.

48 Volt vehicle electrical system: Higher electrical output for the subsystems

Although pure EV technology offers lower-emission mobility, it does not yet achieve the range and comfort of vehicles with internal combustion engines. The short-term solution for traditional car manufacturers is, therefore to increasingly equip their vehicle fleets with hybrid drives. Such a change will certainly lead to considerable emission reductions and lower fuel consumption, without suppliers having to make the leap to fully battery-powered electric vehicles.

This process of hybridization began with simple measures such as switching traditional motor-driven subsystems to electric motor drives and ends with a tightly interwoven, co-dependent combination of electric and combustion engine systems to provide both the vehicle's drive power and the subsystems' electrical power. The greater electrical power required for this strategy will force today's 12 V and 24 V vehicle electrical systems to be converted to 48 V. This will require the use of a new power supply system, which is based on the new 12 V and 24 V electrical systems. This approach is driven by top OEMs such as Audi, BMW, Ford, Mercedes, Porsche and VW - and standardized by organizations such as ISO.

Why 48 Volt?

Firstly, the higher operating voltage compared to a 12 V vehicle electrical system reduces resistance losses during energy transmission. Secondly, the higher on-board voltage enables more powerful electric motors and generators. Thirdly, 48 V is below the 60 VDC safety threshold, above which, standardization bodies require greater shielding and physical protection for electrical systems.

The hybridization journey started in 1997 with the Toyota Prius

The Toyota Prius, introduced in 1997, showed what might have seemed surprising at the time: the fuel and emission savings outweighed the additional costs, weight and complexity of using additional batteries, an engine/generator, complex wiring harnesses and more sophisticated control systems. Since then, a whole taxonomy of hybrid drives has emerged.

Drive solutions: Micro hybrid, mild hybrid and full hybrid

Let's start with the simplest solution. The micro-hybrid uses a 5kW 12V motor/generator to facilitate starting and braking vehicles. This form of hybrid can switch off the combustion engine at idle and restart it immediately if necessary. When the driver takes his foot off the accelerator, the engine/generator helps to slow the vehicle down by converting part of the kinetic energy into electrical energy to recharge the onboard battery via this recuperation. According to industry estimates, this approach can reduce CO2 emissions by up to 4%.

The mild-hybrid (MHEVs for short) goes one step further by using an additional 48 V vehicle electrical system and offering an additional feature: At around 5 to 13 kW, its engine/generator is powerful enough to give the powertrain additional torque. This can be used to start faster from a standstill or generally to accelerate faster. There are two advantages to this fill-and-boost strategy. The first is that the torque of the electric motor is immediately available, which improves immediate responsiveness. Secondly, it can help to keep the combustion engine as close as possible to its most efficient operating point. According to industry estimates, this approach can reduce emissions by up to 21%.

The well-known full hybrid, whose 20 to 40 kW motor-generator has enough power to drive the vehicle alone, requires a much larger and heavier battery to store the required energy. On the other hand, this approach can reduce emissions by up to 30%. A plug-in hybrid that also uses external charging stations to charge its batteries can reduce emissions by up to 75%, while a fully-fledged electric car has no emissions at all - at least not from the vehicle itself.

The 12 V ecosystem remains intact

The automotive industry has built up a huge ecosystem around the 12 V wiring system. But it does not have to give up this when it switches to 48 V systems. Almost all hybrid vehicles, therefore, operate dual-power vehicle electrical systems and battery systems in order to meet the requirements of both the 12 V ecosystem and the emerging 48 V appliance types. Each of these forms of hybrid drive also requires additional electronics. A 12 V micro-hybrid usually requires a voltage stabilization system and a dual battery manager.

Vehicle electronics: Almost all hybrid vehicles operate dual-power vehicle electrical systems and battery systems to meet the requirements of both the 12 V ecosystem and the emerging 48 V device types.
Vehicle electronics: Almost all hybrid vehicles operate dual-power vehicle electrical systems and battery systems to meet the requirements of both the 12 V ecosystem and the emerging 48 V device types.
(Bild: Avnet Silica)

Mild hybrids require belt-driven 48 V starters/generators and 48 V DC/DC converters to control the energy flow between the 48 V and 12 V systems. Full hybrid, plug-in hybrid and all-electric vehicles also operate their batteries at much higher voltages and therefore require a range of high-voltage power electronics systems and high-voltage axle drive motors/generators to operate the vehicles. The challenge and opportunity for automobile manufacturers, subsystem manufacturers and component suppliers is therefore to use the changeover to 48 V to create a great deal of scope for innovation in the industry.

For example, adding a parallel electrical subsystem to an existing internal combustion engine vehicle requires additional space, so component and subsystem manufacturers must increase the level of integration of their offerings. Cable harnesses and connectors are complex and expensive, so innovations in this area are always welcome. There are many ways to offer even more efficient, compact and robust power electronic components for use in vehicles.

MC33771B Lithium-Ion Battery Manager from NXP

Some automobile manufacturers, for example, are developing electric cars with 48 V batteries and ranges of up to 150 km for use in urban areas. These may well require new onboard chargers and battery managers that can be controlled with battery management subsystems such as those from NXP. The MC33771B lithium-ion battery manager for up to 14 battery cells, for example, offers functions for current balancing between cells and also meets the requirements of the ISO 26262 vehicle standard for functional safety.

FTCO3V85A, power module for 48 V DC/DC conversion from On Semiconductor

Another important factor in the transition to 48 V is the compact, efficient DC/DC conversion offered by companies such as ON Semiconductor through highly integrated and automotive-qualified power modules. The FTCO3V85A, for example, is an 80 V, low Rds(on) power module with a three-phase MOSFET module for 48 V DC/DC conversion. It includes a precision shunt resistor for current measurement, an NTC resistor (thermistor) for temperature measurement and an RC suppressor circuit. It is part of a complete family of dedicated power modules based on proprietary injection molded technology specifically addressing 48V applications. For example, functions such as 48 V belt starter/generator, battery disconnect unit, turbocharger and other 3-phase motor units for auxiliary and auxiliary functions are supported.

More Efficient Power Transistors from Infineon and On Semiconductor

Automotive systems also require more efficient and robust power transistors. Some suppliers such as Infineon or ON Semiconductor have already responded: For example, Infineon is using trench technology and lead-free TOLL or TOLG packages to build base devices for 48 V applications in the OptiMOS 80 V/100 V. The new OptiMOS 80 V/100 V is a lead-free TOLL or TOLG package. ON Semiconductor has introduced the FDBL8636x, a new family of PowerTrench MOSFETs with a very low impedance 80V/100V N channel in a compact TOLL package. It is said to be particularly well suited for high-current 48 V applications.

Flexibility in powertrain components

The fluid transition of the hybrid and electric car market also offers suppliers the potential to experiment with different variants in the distribution of key powertrain components. With the L9907, for example, STMicroelectronics offers a Smart Power FET driver for three-phase brushless DC motors. It is integrated into the company's BCD-6s process and can independently control six external FETs, enabling different control strategies for three-phase brushless DC motors.

With the E523.52 - a programmable, brushless high-voltage motor controller for 24 V and 48 V passenger cars and commercial vehicles - Elmos has chosen an alternative path. It has three half-bridge drivers, an 11 V DC/DC step-down converter, two linear controllers and a 16-bit RISC microcontroller with 32 KB flash memory. The 11V output can supply six gate drivers, internal linear regulators, and external loads such as external Hall sensors. Each of these two approaches has its advantages. The exciting thing about the electric drive market is that there is still room to experiment with different approaches to motor control and energy management, and suppliers are willing to provide the parts.

Getting Started with 48V Systems

One of the most exciting opportunities for vehicle manufacturers to switch to hybrid vehicles is to increase the software share of their vehicles so that they can be brought to market faster, adapted locally and even become platforms for new revenue streams through the provision of on-board services. The challenge, however, is to find engineers with appropriate experience in 48-volt power systems.

Software developers are also needed who can develop code that meets the stringent requirements of automotive standards such as ISO 26262 and is protected from attack. As a result, distributors such as Avnet Silica already see a significant increase in demand for support in implementing secure subsystems and interfaces to key 48V applications such as inverters, DC/DC converters and battery management systems. These developments must proceed smoothly.

After the replacement of the horse by the combustion engine, the switch to 48 V hybrid and battery electric vehicles is probably the next big step in the development of cars. So the German automotive industry and its suppliers should no longer waste too much time with trial & error.

This article was first published in German by Next Mobility.

* Gregor Knappikis an employee of Avnet Silica.