Researchers bring contactless power transmission to public transport

July 07, 2011 // By Christoph Hammerschmidt
Electric mobility drives research on inductive power transmission: The Karlsruhe Institute of Technology (KIT) has launched a project that aims at inductive power transmission. The approach of the KIT researchers opens interesting perspectives - it even could be applied during the ride.

A research group around Peter Gratzfeld, head of the KIT Institute of vehicle system technologies, has already proved that it is possible to transfer electric powers in excess of 100 kW by means of inductive coupling to a streetcar - while the railway vehicle was driving. The advantage is obvious: Today's systems with catenaries and collectors are prone to mechanical stress and wear. An inductive, wireless system would do away with these problems - and it could be used in places where for esthetic reasons a catenary is not desired, such as historic city centers. This part of the research project has been conducted in cooperation with rail vehicle manufacturer Bombardier.

Now the researchers have a new goal: They want to apply this technology to non-rail vehicles. City buses are Gratzfeld's next target. "City buses move along defined routes", the researcher said. "This makes it easy to recharge them at stops or even during the ride". With electric cars however, the technology cannot yet be used as long as they are moving. For the time being, the researchers content themselves with charging the e-car batteries when they are parked.

Their power transmission system is designed in a conventional topology: A coil at the vehicle's bottom receives the electromagnetic energy from its counterpart embedded in the tarmac. In contrast to earlier designs, the KIT researchers take into account the protection of nearby persons. Specific coil geometries make sure that the field strength does not exceed the legal limits. In addition, the researchers have implemented a protection circuit that blocks the primary coil from being powered unless the vehicle is positioned exactly above it.