Novel Electric Vehicle Traction Architecture With 48 V Battery and Multi-Input, High Conversion Ratio Converter for High and Variable DC-Link Voltage

Abstract

A new architecture for electric vehicle (EV) traction system with multiple low-voltage battery packs and high conversion ratio DC-DC converters is proposed here. In EV traction systems, higher voltage motors offer improved efficiency and power density. High power DC fast charging also favors charging at high DC voltages to limit the charging cable current to manageable levels. However, the optimum battery voltage is relatively low considering factors such as issues with large number of cells in series and safety. The proposed architecture with multiple 48 V battery packs and integrated, multi-input, high conversion ratio converters (HCRC), can reduce the maximum voltage in the vehicle during emergencies to 48 V and provide a variable, high voltage DC link. It enables independent charging/discharging control of the different low-voltage battery modules ensuring cell balancing and enhancing reliability. The proposed topology significantly reduces the voltage stress and peak/RMS current stress of the switches. It features seamless bi-directional power flow characteristics, which supports regenerative braking and high voltage DC fast charging. Four distinct configurations are analyzed and the configurations with interleaving are shown to improve performance and significantly reduce the filter inductor size. The proposed HCRC operation for EV application is verified experimentally through a 4-phase multi-input, 4 kW hardware prototype. With the nominal input fixed to 48 V, the output voltage is controlled to vary between 200 V to 800 V. The converter achieves a peak efficiency of 98.36% and a full-load efficiency of 97.3% at 50 kHz switching frequency for the interleaved configuration.

Keywords

• Bi-directional DC-DC converter
• electric vehicle traction system
• high gain
• non-isolated boost
• variable DC link voltage
• wide conversion ratio