KAIST rolling out dynamic wireless charging in buses in South Korea
8 August 2013
|The OLEV bus in Gumi. Click to enlarge.|
The Korea Advanced Institute of Science and Technology (KAIST) is trialing a bus application for its Online Electric Vehicle (OLEV) technology, a dynamic wireless charging technology that recharges a vehicle’s battery while the vehicle is in motion. (Earlier post.) An OLEV bus thus requires no pantographs to feed power from electric wires strung above the tram route.
Following the development and operation of commercialized OLEV trams (at an amusement park in Seoul) and shuttle buses (at KAIST campus), respectively, the city of Gumi in South Korea, beginning on 6 August, is providing its citizens with OLEV public transportation services. After the successful operation of the two OLEV buses by the end of this year, Gumi City plans to provide ten more such buses by 2015.
Two OLEV buses will run an inner city route between Gumi Train Station and In-dong district, for a 24 km (15 mile) roundtrip. The bus will receive 20 kHz and 100 kW electricity at an 85% maximum power transmission efficiency rate while maintaining a 17 cm air gap between the underbody of the vehicle and the road surface.
OLEV receives power wirelessly through the application of the “Shaped Magnetic Field in Resonance (SMFIR)” technology. SMFIR is a new technology introduced by KAIST that enables electric vehicles to transfer electricity wirelessly from the road surface while moving. Power comes from the electrical cables buried under the surface of the road, creating magnetic fields. There is a receiving device installed on the underbody of the OLEV that converts these fields into electricity.
|Schematic diagram SMFIR technology. Click to enlarge.||Schematic of shaped magnetic field Click to enlarge.|
The embedded power cable can generate a 20 kHz electromagnetic field when the cable gets 20 kHz AC electricity from the power inverter, which is controlled under constant current output.
The power converter takes electricity from the grid with the typical industrial power of 3-phase 380 or 440V. For the bus application, the power capacity of the power inverter has been selected with a 100-200 kW range; it can be scaled up depending upon required electric load for applications.
The pick-up coil sets under the vehicle are tuned to to the 20 kHz resonant frequency, and are designed to have maximized exposure to the generated magnetic field—which has an optimized field shape for the same purpose. In this way, KAIST says, the transmission efficiency can be maximized while reducing leakage outside of design-intended space.
The length of power strips installed under the road is generally 5%-15% of the entire road, requiring only a few sections of the road to be rebuilt with the embedded cables.
The OLEV has a small battery (one-third of the size of the battery equipped with a regular electric car). The vehicle complies with the international electromagnetic fields (EMF) standards of 62.5 mG, within the margin of safety level necessary for human health, according to KAIST.
The road has a smart function as well, to distinguish OLEV buses from regular cars—the segment technology is employed to control the power supply by switching on the power strip when OLEV buses pass along, but switching it off for other vehicles, thereby preventing EMF exposure and standby power consumption. As of today, the SMFIR technology supplies 60 kHz and 180 kW of power remotely to transport vehicles at a stable, constant rate.
It’s quite remarkable that we succeeded with the OLEV project so that buses are offering public transportation services to passengers. This is certainly a turning point for OLEV to become more commercialized and widely accepted for mass transportation in our daily living.—Dong-Ho Cho, director of the Center for Wireless Power Transfer Technology Business Development at KAIST
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