Evaluation of Electrical Loads on 48 V Supply in Future Mild Hybrid Electric Vehicles

Abstract

Today, the automobile industry is driven by the urge to reduce emissions and to achieve the low CO2 emission targets that are set by the European Legislation to reduce the average CO2 emissions of a manufacturer's eet below 95 g/km by 2021. This has led to the focus on Mild Hybrid technology. This involves the introduction of a higher system voltage i.e. 48 V. However, the initial generation of Mild Hybrid Electric Vehicles is expected to have both 48 V and 12 V systems. The purpose of this study is to evaluate the potential benefits of shifting electrical loads to the 48 V supply in the future Mild Hybrid Electric Vehicles at Volvo Car Corporation (VC). A literature study has been carried out to identify the loads on the existing 12 V automotive electrical network that could be considered to be suitable for a 48 V operation. The whole system has been modelled in MatLab R Simulink R and simulations were carried out to evaluate their performance at three temperatures (􀀀20C, +20C and +40C). The savings in fuel consumption due to moving of loads to the 48 V bus have been analysed. Also, new loads that could improve the user experience have been identified. The complete system has been evaluated for its electrical performance and fuel consumption. The weight reduction by shifting loads to the 48 V bus have also been looked into. The results suggest that the 48 V mild hybrid system efficiency is high during high loading condition primarily due to the increased efficiency of Belt Driven Starter Generator (BSG). The fuel savings at 20C, +20C and +40C have been estimated to be 376 ml/100 km, 32 ml/100 km and 103 ml/100 km respectively for the WLTP cycle. The considerable benefit on reduced fuel consumption is also due to the higher amount of energy that is recuperated at 48 V. Due to these abilities of the BSG, it is still advantageous to supply the present day 12 V electrical network from a 48 V BSG through a DC/DC converter. The PTC heaters, defrosters, blowers, EPS, cooling fan and fuel pump could be supplied from a 48 V network in the initial generation of MHEVs.