Researchers have discovered that bidirectional charging enables electric vehicles (EVs) to be charged and discharged as needed, therefore making them suitable for use as mobile electricity storage units.
To ensure that bidirectional charging can be used at a large scale, the team is researching innovative charging technologies that can contribute to the increasing flexibility of the energy system.
The research project, titled GaN4EmoBiL, will develop new semiconductor, device, and system technologies for an 800 V class EV.
How does bidirectional charging work?
Bidirectional charging allows electric vehicles to be charged with electricity from renewable sources.
Furthermore, vehicles can be discharged as needed during periods when no wind or solar energy is being produced.
This additional electricity could be used for other electrical devices or supplied to the power grid, which contributes to energy security.
However, previous technological approaches do not meet the demands for cost and efficiency. There is a lack of intelligent and cost-effective bidirectional charging systems to connect batteries, the grid, local generators and consumers with high efficiency and high power density.
This is where the GaN4EmoBiL project comes in.
The aims of the GaN4EmoBiL project
The Fraunhofer Institute for Applied Solid State Physics IAF, the University of Stuttgart, Robert Bosch GmbH, and Ambibox GmbH have taken on the challenge of meeting the cost and efficiency demands associated with bidirectional charging.
The team’s goal is to develop an intelligent and cost-effective charging system using new semiconductor devices, device concepts, and system components.
The three-year project is funded by the German Federal Ministry of Economic Affairs and Climate Action (BMWK) as part of the Elektro-Mobil programme.
Dr Stefan Mönch, researcher in the field of power electronics at Fraunhofer IAF and project coordinator, commented: “Our project aims to connect batteries, renewable energies and electrical consumers in an economical and flexible way.
“Through bidirectional charging solutions, the previously unused batteries of parking electric vehicles will make a greater contribution to increasing the flexibility of the energy system and avoiding CO2 emissions in the future.”
Dr Etienne Tchonla, R&D Director at Ambibox, added: “In the future, efficient, small-scale, and intelligent charging infrastructures in electromobility will contribute to overcoming social challenges.”
New semiconductor solutions to achieve maximum efficiency
To date, initial bidirectional charging medium-power DC wallboxes for batteries up to 800 V use power semiconductor devices, which are not yet optimal for this application.
They are either efficient but expensive (silicon carbide) or low-cost but less efficient (silicon). Moreover, 650 V transistors made of gallium nitride on silicon (GaN-on-Si) are inexpensive and efficient, but require a complex circuit due to insufficient voltage rating.
To integrate as many batteries as possible bidirectionally, the cost, efficiency and compactness of charging solutions must be significantly improved. For this purpose, the project partners of GaN4EmoBiL are researching new semiconductor solutions.
They want to develop a new cost-effective GaN technology on alternative substrates, which enables low-cost and efficient 1200 V transistors. They are developing new system components (bidirectional charging cable and charger) and investigating their reliability for significantly increased operating hours.
At the end of the project, demonstrators should fill the research and development gap currently existing between cost, efficiency, compactness, functionality, power class, and voltage class (800 V batteries).
Overall, the researchers aim to promote knowledge transfer between universities, research institutions and industry, train young scientists, and secure national know-how in the field of electromobility.
