Split-voltage E/E architecture takes shape
Car maker Audi acknowledged the plans to equip next-generation passenger cars with an additional 48 V supply network, communicated a week earlier in a joint statement of all German OEMs. According to Audi, the 48 V supply network will be implemented first in standard cars with Internal Combustion engine. "Our first roll-outs won’t include electric vehicles", the company said. Roll-out of first production vehicles will be within three years. Nevertheless, in the mid-term, the goal is to include HEVs as well.
Not all companies involved wanted to talk openly about the topic. Luxury car maker Daimler, for instance, backpedaled and declined to provide any further details – after Daimler E/E expert Volker Wilhelmi had assumed the role of a spokesman in the joint statement. Nevertheless, in talks with various experts eeNews Europe was able to identify the most significant building blocks for the split-voltage architecture.
In fact, the issue is not new; the industry has been discussing a higher supply voltage for high-current applications for more than ten years. But the voltages in discussion as well as the goal for introducing a higher voltage have changed. In the beginning, the focus was on performance and features – for instance, the industry intended to implement advanced systems like steer-by-wire, brake-by-wire, or electric valve control. "Now it is all about CO2 emission reduction", explained Alfons Graf, System Architect for vehicle body systems for Infineon. "In the meantime, the performance topics have been resolved otherwise or became obsolete", he said. Currently, the rationale to implement 48 V is "micro-hybridizing" the cars, with improved recuperation and other measures in the focus. "Also the battery technology has changed", Graf said. "In the beginning it was all about lead acid batteries, now the considerations focus on lithium-ion".
Experts such as Graf expect that within the 12 V domain most elements will remain in place – including market factors such as growth expectations and product strategies. However, the car’s generator will be shifted to the 48 V section; the 12 V section will be coupled to the 48 V section by means of a bidirectional DC/DC converter with some 3 kW. Since the 48 V generator will during certain phases function as a motor, an 48 V inverter that controls the motor/generator will be added. Also a new 48 V battery will be added. Unlike "dumb" lead-acid batteries, this battery will be implemented as Lithium ion battery with significant effort for the management system.
Several high-current power consumers will be associated to the 48V side. Examples could be blowers for engine cooling as well as for HVAC, power steering, PTC auxiliary heaters, or electric power steering. In addition, the high voltage makes it relatively easy for carmakers to implement new energy saving functions such as "coasting": In contrast to existing micro hybrid systems, the combustion engine is not only switched off when the car stops but already when it drives along with decreasing speed. This would help OEMs to squeeze out some additional percents of fuel consumption. In such a coasting situation, it is essential to have a stable supply voltage since all 12 V systems (lighting, safety functions etc) have to remain completely active without any compromises. For this reason, the DC/DC converter connecting both supply networks is critical.
In the semiconductor industry, the roll-out plans could create some hectic design efforts. Existing product lines for 12 V are not suited for deployment in 48 V applications. Infineon’s Graf pointed out that the company already has significant expertise in 24 V systems through its strong position as supplier for the truck market. "We already have volume products that meet the requirements for 48 V", Graf said. "Nevertheless, the portfolio is far less dense populated than the 12 V portfolio". But not only Infineon will encounter this challenge but the entire semiconductor industry.
Is 48 V a welcome opportunity to bring new semiconductor technologies to market such as Silicon Carbide? No, Graf said. "This voltage can be handled perfectly with standard silicon transistors".
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