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. In some designs, a boost DC-DC converter is employed to accommodate large variation in battery voltage and provide a high DC link voltage. However, the DC link cannot go below the battery voltage (for example, 360 V) which limits the benefits of the DC-DC converter. The proposed architecture with multiple 48 V battery packs and integrated, multi-input, high conversion ratio DC-DC converters, can reduce the maximum voltage in the vehicle during emergencies to 48 V, mitigate issues with large number of cells in series, and provide a wide variable DC link voltage. 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 support 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 high conversion ratio converter (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.

Review of Electric Vehicle Charging Technologies, Standards, Architectures, and Converter Configurations

“…20 (a). The interleaved boost converters can provide better performances by reducing input/output ripples, conduction losses, high power, reduced size, and EMI in EV energy storage systems [284]. In [285], the boost PFC converter is presented with soft switching techniques to minimize the heating problem in the diode bridge and losses in boost diodes.…”

Performance Analysis of a High Gain Bidirectional DC-DC Converter Fed Drive for an Electric Vehicle With Battery Charging Capability During Braking

“…The DC-DC converter must be bidirectional because the forward mode will face transient and overload conditions during which power gets transferred from the battery to load and during the reverse mode, the battery pack has to get charged. Some of the benefits derived by providing a BDC between the battery and the inverter [4], [5] are: a) It reduces the stress on the inverter with an additional DC stage b) It adjusts the inverter supply voltage to increase the motor output, c) The cost and size of the battery can be reduced because of lower cell count requirement and d) The system voltage and battery can be individually designed by the manufacturers. This architecture thus enables versatile system designs for vehicles with various output characteristics.…”