Integrated DC fast charger in an electric vehicle

University essay from Lunds universitet/Industriell elektroteknik och automation

Abstract: More and more electric vehicles are emerging with a nominal battery voltage higher than what most older DC fast chargers are capable of charging. This requires the vehicle manufacturers to include a high power DC to DC converter in order to be able to charge at these stations, adding cost and complexity. Instead, with only minor modifications of the traction system, the motor and inverter can be used as three parallel DC to DC converters, removing the need for an extra converter. The aim is to develop, assemble and test a low voltage system that can run at about the same current level as existing charging stations. Its performance is assessed and the measured efficiency is compared to a theoretically derived one. The results are then extrapolated to a higher voltage in order to investigate its feasibility. The system is proven to work satisfactorily at the low voltage, although with quite poor efficiency of about 80% at around 5 kW charging. When increasing the voltage the efficiency seems promising although some concerns are raised about the increased current ripple.

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