Wireless energy transfer strips for electric vehicles and buses

Wireless energy transfer strips for electric vehicles and buses


The Korean KAIST online electric vehicle (OLEV) bus [Image source: KAIST, via Wired Magazine]

Alongside innovative battery technology, another potential method for charging electric vehicles (EVs) could be wireless energy transfer strips installed on road surfaces. The potential for new electric vehicles is quite exciting, particularly with regard to mass transit vehicles such as buses and trams, but the technology could one day be used for EVs also.

Wireless transfer was first demonstrated by Nikolai Tesla in 1891. Tesla had an obsessive interest in the subject which enabled him to develop his Tesla Coil. This device, which produces high voltage, high frequency alternating currents, enabled Tesla to transfer power over short distances without interconnecting wires via resonant inductive coupling, the near-field wireless transmission of electrical energy between two magnetically coupled coils.

This approach is increasingly being tested in various countries as a potential means of charging EVs on the move. It involves the transfer of electricity between two magnetically-charged plates, one of them buried in beneath the road or railway and the other slung beneath the chassis of a vehicle. In Italy, such a system has been in use in Genoa and Turin for over ten years, providing 10 to 15 percent of the power for 30 electric buses which recharge at each bus stop. The system was developed by a German company, Conductix-Wampfler, which claims a 95-percent energy-transfer efficiency. Another system is currently under development at Utah State University, supported by funding from the Federal Transit Administration and an induction system also launched in The Netherlands in 2010.

In 2009, the Korea Advanced Institute of Science and Technology (KAIST) tested its Online Electric Vehicle (OLEV) project. This incorporated a technology called the Shaped Magnetic Field in Resonance (SMFIR) involving the burial of electric power strips at a depth of 30 cm (11.8 inches) beneath the road surface, connected to the national grid. A trackless train was used as the demonstration vehicle, consisting of a tractor fitted with magnetic induction pick-ups and three passenger carriages. KAIST subsequently deployed trams using the system at the Seoul Grand Park Amusement Park and followed this with the world’s first electric bus in July 2013, travelling for a distance of 15 miles between the train station in the city of Gumi and the district of In-dong. By then, the initial project had already led to the formation of two spin-off companies, OLEV Korea and OLEV Boston, the latter launched in 2011 and which is aiming to commercialize its system for use in the US.

The KAIST OLEV bus in operation in the Korean city of Gumi [Image source: KAIST]

The wireless transfer system means that batteries in electric vehicles can be reduced in size to about a third of that you would normally expect to find in an electric car. A gap of 6.7 inches between the road surface and the bottom of each vehicle delivers an 85 percent charging efficiency at 100 kilowatts. The plates buried beneath the road surface account for between 5 and 10 percent of the entire route and remain switched off until a vehicle approaches. It takes about 30 minutes for OLEV to fully charge and they can travel for 40 kilometers between charges (about 24 miles) and that means they could potentially veer off the established charging route on occasion if they needed to. The buses can travel at a top speed of 85 kilometers per hour (km/h) but usually travel at 60 km/h in ordinary service.