October / November 2021

www.vicorpower.com AUTOMOTIVE POWER 31 www.power-mag.com Issue 4 2021 Power Electronics Europe Is the 12V Lead-Acid Battery Dead? Yes, the 12 V 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. While this may seem like a daunting task, it also presents a tremendous opportunity to eliminate the environmentally toxic battery while also reducing weight in a vehicle and improving overall efficiency. Nicolas Richard, Director Automotive Business Development, Vicor Europe T he 12 V battery and power delivery network (PDN) are standard across the globe, supporting hundreds of loads, including some critically related to safety, so the solution will need to be both innovative and robust. High-density, high- power and efficient power modules used to interconnect high-voltage, 48 V and 12 V PDNs offer the most flexible and scalable solution to this impending challenge. When considering potential solutions, OEMs must take into account a number of key factors: adding more power to support new features with better performance, increasing efficiency for longer range and better thermal management, reducing CO2, optimizing cable routing, reducing harness weight and meeting EMI requirements are some of the variables within this complex equation. There are two primary options for solving this equation. Replacing the 12 V lead-acid battery with a 12 V Li-ion battery is one option. While it does slightly reduce weight, it retains the decades-old legacy of the 12 V PDN, which yields no additional benefits. The other option is to support a 12 V PDN powered from the primary 400 V or 800 V battery in EV and HEV/PHEV. There are many benefits to the latter option, but both merit further exploration. Switch to 12V Li-Ion battery Simply replacing the 12 V lead-acid battery with a 12 V Li-ion battery saves ~55 % weight; however, it has a high cost impact. The 12 V Li-ion battery needs a Battery Management System (BMS) to control the charging and maintain the full battery operation over the vehicle life. It is the direction taken for instance by Tesla [1] and Hyundai [2]. Furthermore, adding a bulky DC/DC converter from HV to 12 V (with voltage and current regulation feature) is needed to recharge the 12 V Li-Ion battery and supply the electrical loads. But this adds no benefits. What it does add is weight, vehicle packaging complexity, and system cost; it also reduces overall vehicle reliability. By contrast, eliminating the 12 V battery altogether removes 13 kg from the vehicle and can improve the cargo space by 2.4 % [3]. Legacy 12 V PDNs are inefficient Maintaining a physical 12 V battery means maintaining an inefficient PDN with unnecessary redundancy. In a typical automotive 12 V PDN, all the 12 V loads connected to the 12 V bus have internal pre-regulators able to convert wide input voltage range typically from 6 to 16 V to regulated rails of 5 V, 3.3 V or lower. From a global system view for an EV, HEV or PHEV, there is redundancy of series regulator stages. A high-voltage-to-12 V DC/DC converter regulates the 12 V bus (with efficiency hit) and the pre-regulator provides the suitable internal rail voltage for each load (Figure 1). This legacy architecture originated when vehicles had an alternator, a sensitive 12 V PDN that needed regulation to charge the battery, keep the radio operating during cranking event or maintain incandescent headlights at the right intensity. OEMs were very creative to bypass the 12 V power limitation and complex electrical architectures have been designed in recent years with two 12 V batteries, one 24 V battery for power steering and several DC/DC converters between them. Replacing the 12 V with a virtual battery A better approach to solving this problem is to completely rethink the PDN in a vehicle: eliminate the physical 12 V battery and replace it with a 12 V “virtual” battery from the primary EV battery (Figure 2). Every EV carries a main battery, so it does not make sense to transport additional energy storage devices. The ideal vehicle architecture would be one high-voltage (HV) battery used to power Figure 1: Typical E/E used in xEVs with 12V battery using redundant voltage regulator stages. The HV- to-12 V DC/DC regulates the 12 V output to charge the 12 V battery. Every 12 V load in the vehicles has a pre-regulator stage to supply the proper rail voltage needed for the load to operate.