A Novel Approach to Affordable Electric Vehicles Based on Dual 48V Battery System with Multi-functional 3-level Converter

Abstract:
Main building block of modern mobility are electric vehicles (EV). Mainstream power supplies of EV are 400 V or 800 V batteries and related to them inverter implementation based on wide-band gap semiconductors like SiC MOSFETs – however, efficiency and corresponding affordability (due to high voltage ratings and service of hazards) remain as a main challenges. Inverter efficiency is mainly influenced by losses in semiconductor power switches – for 400 V and higher battery voltages, high-voltage switching components must be used (650 V and higher). Based on experiences with 48 V mild hybrid vehicles, this paper gives an alternative approach for affordable smaller size EVs. 48 V as single voltage is not enough to cover the efficiency requirements of the whole driving cycle, therefore a dual power supply with two batteries (+/- 48 V, with a common ground connected to the chassis as shown on Fig. 1) was considered. In a 2-levele topology is difficult to find optimal power switches for 96 V DC bus, therefore the 3-level topology, Active Neutral Point Clamping (ANPC) inverter, based on 80 V MOSFET was implemented. Additionally, two-battery system requires active battery balancing, which is typically implemented as additional DC/DC converter – in this paper is presented a novel idea of battery balancing by simply selecting optimal voltage vectors of Space-Vector Modulation (SVM) and on that way avoiding need for additional hardware – with this approach system costs are reduced and overall system efficiency is increased.