Column: Electric Vehicles
Leveraging an EV’s high-voltage battery to deliver 12V more efficiently
By Nicolas Richard, Director Automotive Business Development – Europe, Vicor S
adly, the 12V lead-acid car battery is dead! Europe has decreed that no new cars will have lead-acid batteries after 2030, creating a
considerable challenge for OEMs to find alternative solutions. Initially this may seem like a daunting task, but it is a tremendous opportunity to eliminate the environmentally-toxic battery, reduce the vehicle’s weight and improve its efficiency. The 12V battery and power delivery
network (PDN) are standard in vehicles across the globe, supporting hundreds of loads, including those related to safety, so the solution will need to be both, innovative and robust. High-density, high-
power and efficient power modules interconnecting high-voltage (HV) 48V and 12V PDNs offer the most flexible and scaleable solution to this impending challenge. But, when considering any solution, OEMs must consider several key factors: the power that will support new features, the efficiencies needed for longer driving range, the thermal management, reduced CO2
, optimised cable routing,
reduced harness weight, the EMI requirements, and a lot more, all of which add to the complexity of the overall problem. There are two primary options for
solving this equation: Replacing the 12V lead-acid battery with a 12V Li- ion battery is one and supporting a
12V PDN powered from the primary 400V or 800V battery in EVs and HEV/ PHEVs is the second. The first option slightly reduces weight, but retains the decades-old legacy of the 12V PDN, with no additional benefits. The second option offers more benefits, but both merit further exploration.
Switching to a 12V Li-ion battery Simply replacing the 12V lead-acid battery with a 12V Li-ion one – a direction taken by Tesla and Hyundai, for instance – saves about 55% of the weight, but with a high cost impact. The 12V Li-ion battery needs a battery management system to control its charging and maintain full battery operation over the vehicle’s life. Furthermore, a bulky DC-DC converter from high voltage to 12V (with voltage and current regulation) is needed to recharge the 12V Li-ion battery. Overall, this adds no benefits but does add weight, vehicle packaging complexity and system cost, and reduces vehicle reliability. By contrast, eliminating the 12V battery altogether removes 13kg from the vehicle and can free the cargo space by 2.4%.
Figure 1: Typical electrical/electronic (E/E) used in xEVs with 12V battery using redundant voltage regulator stages. The HV-to-12V DC-DC regulates the 12V output to charge the 12V battery. Every 12V load in the vehicle has a pre-regulator stage to supply the proper rail voltage needed for the load to operate
14 November 2022
www.electronicsworld.com
Inefficient legacy 12V PDNs Maintaining a physical 12V battery means maintaining an inefficient PDN with unnecessary redundancy. In a typical 12V automotive PDN, all the 12V loads connected to the 12V bus have internal pre-regulators converting wide input voltage ranges (typically 6-16V) to regulated rails of 5V, 3.3V,
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