Increasing the range of electric shuttle buses with wireless charging

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Increasing the range of electric shuttle buses with wireless charging

Bailey, J. Ronald / McBath, Justin / Hairr, Mark E.

The range of an electric shuttle bus has been increased from less than 50 miles on batteries alone to more than 120 miles by wireless charging during the period when passengers are normally boarding the bus. The Center for Energy, Transportation and the Environment at the University of Tennessee at Chattanooga in partnership with the Chattanooga Area Regional Transportation Authority (CARTA), EVAmerica, and Embedded Power Control (EMPCON) with support from the Federal Transit Administration (FTA) under Cooperative Agreement TN-26-7034, has demonstrated wireless charging for electric shuttle buses using Inductive Power Transfer (IPT) technology provided by Conductix Wampfler, AG. The system includes a track supply that provides power at 20 kHz to a coil embedded in the roadway. The power is transferred to the bus through an air gap to pick-up coils mounted on a mechanism under the bus that drops the coil into position 40 mm above the embedded coil. This short "opportunity" charge of three minutes duration at 60 kilowatts provides enough traction energy to power the bus for approximately three miles, thereby eliminating the normal range constraint that, until now, has required battery swapping during the day to cover the required daily route of 100 miles. Overall efficiency from the grid to the vehicle was found to be more than 90%, resulting in an energy cost per mile of less than .10 while producing zero tailpipe emissions. Measurements of electromagnetic field strength at the edge of the coils near street level and at all locations inside the bus have been found to be well below draft international standards for exposure.