Introducing mild hybrid vehicles was the fastest, cheapest and thus most logical step for many automobile manufacturers to ensure that their vehicles satisfied the CO2 limits imposed by the European Commission. The 48V on-board power systems required for this are usually achievable with reasonable investment. It enables features such as regenerative braking, temporary storage of energy in battery packs and capacitors, and subsequent electrical support for a conventional combustion engine. This itself reduces consumption and emissions with percentages in the low double digits.
Figure 1 shows how the market share of electric vehicles would have to develop in order to comply with future limits. It is immediately apparent why the 48V on-board power system is only seen as a transitional technology while a sufficiently large fleet of high-voltage (HV) battery electric vehicles (BEVs) becomes established.
The Best Way to Reduce CO2 Emissions
A purely electrically powered car with zero local emissions seems to be the ideal solution for fulfilling CO2 emission requirements that will only get stricter as time goes on, which is why development and funding needs to be provided to this end. Relying entirely on HV electromobility is not the right solution though. The advantages and disadvantages are already a topic of heated discussion.
There are concerns that focusing on HV electromobility may cause development of promising alternative concepts such as fuel cells or carbon-neutral synthetic fuels to suffer, resulting in the neglect of potentially key technologies. Also, when you consider the entire value chain as a whole, it becomes apparent that it will be unfeasible to achieve a global shift towards purely electrical vehicles in a carbon-neutral fashion, and this will remain the case for years to come. In particular, the current energy mix of nuclear energy, fossil fuels and renewable sources and the production and recycling of batteries have a negative impact on our carbon balance.
One of the challenges in the use of batteries is that the requirements placed upon the overall electric vehicle system can vary greatly depending on the conditions it is to be used in. In extreme and/or greatly variable environmental temperatures, efficient heating/cooling solutions that are adapted to such conditions are necessary to guarantee the safety and reliability of the battery and the system as a whole. This too is a new area of development.
The time it takes to create a carbon-neutral electromobility concept and how 48V on-board power systems can help achieve this will be critical. This will reveal whether 48V on-board power systems are only a transitional automotive technology or if there is more potential within.
48V Approaches for the Future
Regardless of whether a vehicle is powered entirely electrically using a battery, or whether it uses a fuel cell or synthetic fuels, 48V power systems in auxiliary power units can help achieve energy savings compared to 12V supplies and also in comparison to HV simplifications for the installation and operation of auxiliary power units in vehicles-thereby offering potential for optimization. Typical 48V applications include e-turbo, electric air conditioning systems with 4 to 5kW, electric heaters such as eCAT (electrically heated catalytic converters), PTC block heaters or windshield de-icers with 1 to 5kW, ERC (electrical roll control) with 1 to 5kW, pumps and fans of up to 1kW and other applications involving high power densities and/or continuous usage. Second-generation mild hybrid vehicles are increasingly achieving these using 48V power systems; 48V systems are also encountered in HV-BEVs as a third power system.
Urban Mobility Ideal for 48V Technology
Urban mobility is a promising business field for 48V technology. Unlike the objectives of current HV-BEV development, which include long distances of more than 400km and short charging times, the focus with urban mobility is on short trips of between 2 and 50km, cost, battery weight and insulation protection. Charging times are irrelevant in urban environments because the vehicle can be charged during working or night hours.
Calculations show that a 30kW motor is adequate to complete urban and extra-urban driving cycles with small compact cars. In this driving cycle, a 48V BEV drivetrain is around 25% cheaper than a HV 400V BEV drivetrain.
Electrically powered commercial vehicles with 48V systems supporting loads of up to 1000kg are already available on the market, among them the "Streetscooter" postal vehicle. Electric motorbikes, scooters and mopeds using 48V power systems are also becoming increasingly established. Some of them even have a replaceable battery system.
All of these vehicles can be created with applications that are being or have already been developed for mild hybrid automobiles, including batteries with battery management systems (BMS), inverters, DC/DC converters and auxiliary power units.
New Requirements Placed Upon Semiconductors
As already mentioned, 48V power systems with any circuit topology already allow for the basic boost and recuperation functions with the combustion engine engaged and gliding while the combustion engine is disengaged. However, when the engine is disengaged, a fully automated forward clutch is essential. Recovery of braking energy while the engine is disengaged and driving on electrical power alone using the capacity of a 48V system on the other hand place new demands on the performance and robustness of semiconductors.
48V on-board power systems also use sensors, microcontrollers, as well as power, supply, communication and driver semiconductors. They control electric motors, handle power distribution in the inverter, and supply auxiliary power units.
Low-loss MOSFETs are often used as power amplifier ICs and are usually controlled, monitored and-if need be-used to recover a safe operating state via three-phase drivers. Key components other than motor driver ICs include high-performance gate driver ICs that, in combination with MOSFETs, allow for the creation of high-reliability battery switches or safety switches for 48V/12V cut-off mechanisms. Electrically, the 48V system is coupled with the 12V system by means of a DC/DC converter.
Bridge driver ICs such as the TLE9180 from Infineon are used as communication and power components.
For 48V applications such as starter generators (belt-driven or integrated), DC/DC converters or main battery switches/cut-off switches, there is high demand for 80V and 100V MOSFETs.
Broad Portfolio for 48V
Numerous semiconductor suppliers are investing not only in high-voltage technologies for electric vehicles, but also in 48V technologies and products. They are already offering a broad, scalable portfolio of powerful semiconductors, including evaluation kits that allow for the creation of all kinds of applications-including those with high specifications, including complete systems and chipset solutions for voltage controllers, smart power drivers and very-low-resistance MOSFETs that are ideal for use in 48V systems.
Investment in 48V Technology Still Worthwhile
This shows that 48V is not just a transitional solution-it will continue to offer a path to low-carbon mobility in the future and will therefore still provide benefits in numerous application scenarios. This means that investments in and system optimizations for the use of an 48V on-board power system will remain worthwhile. Appropriate components are already available.
Find components at www.rutronik24.com.
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