48V in MHEVs vs. BEVs

In the late 1990s, there was a push for 42V E/E systems. But OEMs abandoned this approach given the lack of high-efficiency motors, and there was a market shift toward MHEVs that used a high-voltage starter generator. Thus, while MHEVs were the “first” 48V systems, they used only a 48V battery and small electric motor to assist the ICE, which reduces fuel consumption and improves efficiency.

The main low-voltage rail powering E/E systems within MHEVs remains at 12V and requires a large bidirectional converter between the 48V and 12V rail, adding a large cost burden. In contrast, full hybrids (HEVs), plug-in hybrids (PHEVs) and BEVs can use the high-voltage battery to create a 48V low-voltage rail to power the entire E/E system.

Because of limited trim lines and platforms, future BEV platforms were the primary target for OEMs to implement 48V automotive systems. The transition to electric-drive vehicles has also increased investments in HEVs and PHEVs. Figure 1 provides an overview of the differences between vehicle types.