Voltage Considerations for Electric Vehicle Propulsion Systems

A total of seventeen different electric vehicle propulsion systems were studied to select two designs which best met established cost and performance goals. Both systems were then examined to assess the effect of battery pack voltage on system performance and cost. The cost of the battery pack was the major factor in system voltage selection. A voltage range of 54 V to 540 V was considered, for battery pack capacity of 24 kW-hr. The highest battery specific energy (W-hr/ Kg) and the lowest cost ($/kW-hr) were obtained at the minimum voltage level.

The voltage considerations for the machinery were different for the two selected designs. The first system has an energy storage flywheel to provide power for acceleration, so the dc traction motor and the battery are not subject to extreme peaks of power demand. The second system uses a brushless dc permanent magnet motor with electronic commutation, supplied by the power control unit must handle the peak power needed for acceleration. The second system is adversely affected when combined with the lowest battery voltage.