Siemens, BMW develop high-speed EV charging system

October 20, 2011 // By Christoph Hammerschmidt
Siemens and BMW have developed a flexible fast transfer charging system for electric vehicles, enabling the driver to charge the battery from AC or DC energy sources using the same connector. Now the companies plan to transfer the concept into an international standard.

The BMW/Siemens approach utilizes the standard AC connector as it has recently been demonstrated by German and American OEMs. However, in the context of the study, the connector system has been enhanced by an additional DC charging function. So far, electric vehicles need two different charging sockets along with the associated power electronic systems - voltage and current regulators as well as a rectifier.

Besides driving range, charging time is one of the paramount criteria for the usability of electric vehicles. While it takes several hours to charge the battery from a standard household AC outlet, DC charging cuts this time span to less than half an hour. Since the converter circuitry for DC charging is not located in the vehicle but in the charging station, DC charged vehicles are cheaper and lighter. This in turn translates into a larger driving range; the short charging cycle could make electric vehicles more attractive for commercial users such as fleet operators. However, for DC charging different charging stations are needed.

The Siemens/BMW approach in the Drive eCharged project has, according to the project partners, several advantages over existing systems: AC and DC charging connectors fit to the same socket in the car. The communication between vehicle and charging station has been harmonized. Thus it becomes possible to support additional functionality such as smart charging and bi-directional charging. With the system, the developers hope to reduce charging times to 15 minutes.

In the context of the project, Siemens has implemented a charging station; the tests have been conducted with a BMW ActiveE prototype electric car. The technology has been submitted to IEC as a standard proposal.