By Isabella Kaminski
According to the Fraunhofer Institute for Solar Energy Systems (ISE) in Germany, the chargers have a 97% efficiency rate. With a rated power of 22 kW, they can load a typical electric vehicle battery to 80% in just 45 minutes.
The charger is a two stage converter. The first stage converts the three phase grid voltage of 400 V AC into a DC voltage. A DC/DC converter is used as the second stage in order to adjust for the varying battery voltage of 300-500 V DC. To save weight, volume and cost while increasing efficiency, a transformerless circuit topology with extra electrical safety measures was used.
The Fraunhofer charger is bidirectional, meaning that it can both energy from the grid for charging and feed energy stored in the battery back into the grid. This enables energy from fluctuating renewable energy sources, such as wind and solar, to be stored in the battery during times of high availability and to be fed back into the grid at times of high grid load and/or reduced renewable energy availability.
The new development was part of the joint Fraunhofer Systems Research Electric Mobility project funded by the German Federal Ministry of Education and Research (BMBF) and involving more than 30 Fraunhofer institutes.