Battery sizing of 48 V plug-in hybrids considering calendar and cycle degradation*

Plug-in hybrid electric vehicles (PHEVs) with battery packs tailored to the driving use case can help to reduce the environmental footprint of the transportation sector. Compared to common high-voltage systems, PHEVs based on a low-voltage level show a higher fuel consumption, but in return benefit from lower component costs and allow the utilization of cheaper high-energy cells. In this paper, the battery size of a 48 V PHEV concept is optimized to minimize the operational costs while taking battery degradation into account and ensure a lifetimerobust system layout. To investigate the applicability of high-energy batteries, 31 automotive-grade cells were investigated experimentally in a calendar and cycle aging study. The results show that calendar aging has a significant contribution of 17.5 % to the overall capacity loss and should be considered during the battery design process. The cycle degradation model is integrated in a Dynamic Programming simulation environment with various real-driving speed and slope profiles, which are extracted from a measured year-round driving profile. The simulation results show, that considering the degradation in the energy management strategy reduces the capacity loss but results in higher operational costs throughout the vehicle lifetime. The extension of a mild hybrid vehicle to a PHEV can reduce the operational costs by 18.5 %. If the vehicle is not charged, the costs increase by 6 % highlighting the need for frequent charging of PHEVs.