GaN module paves the way for compact and cost-efficient bidirectional 800 V charging systems

In the GaN4EmoBiL research project (“GaN Power Semiconductors for Electromobility and System Integration Through Bidirectional Charging”), the Fraunhofer Institute for Applied Solid State Physics IAF, the University of Stuttgart, Robert Bosch GmbH, and Ambibox GmbH jointly developed new semiconductor, device, and system technologies for bidirectional charging in the 800 V class. The project focused on high-voltage GaN transistors on low-cost alternative substrates, bidirectionally blocking power switches, and AC and DC chargers. The three-year project was funded by the German Federal Ministry for Economic Affairs and Energy (BMWE) under the “Elektro-Mobil” program.

The project was based on the vision of not only charging electric vehicles, but also using their batteries as flexible electricity storage systems—for example, to store surplus solar or wind power and feed it back into the grid when needed. Until now, however, charging solutions have often been limited by an unfavorable balance of cost, efficiency, and compactness. This is where GaN4EmoBiL came in.

GaN module demonstrated in a mobile off-board charger

As a key result, Fraunhofer IAF developed a gallium nitride-based power electronics module for 800 V-class bidirectional DC charging systems. The module uses 1,200 V-class GaN devices fabricated on an insulating substrate and delivers high efficiency at comparatively low cost. Project partner Ambibox integrated the module into a demonstrator of a bidirectional, single-phase off-board charger with an output of up to 3 kW.

With a total volume of 8.3 liters and a weight of 5.7 kilograms, including connectors, the demonstrator is significantly more compact and portable than on-board chargers permanently installed in vehicles. These chargers currently convert alternating current from household outlets or public charging stations—such as 11 or 22 kW systems—into the direct current required by electric vehicles.

“The demonstrator shows that even low-power external off-board chargers can be designed to be particularly compact and mobile while enabling bidirectional charging directly with DC via the CCS connector. GaN-based power electronics in the 1,200 V class offer significant potential for highly efficient and cost-effective charging systems,” explains Junior Professor Dr. Stefan Mönch, coordinator of the GaN4EmoBiL project.

Although its charging speed is lower than that of more powerful on-board systems, the device is mobile and can be used flexibly via its CCS connector and grounding-type plug.

Bidirectional charging as a building block of the energy transition

“Gallium nitride has long been largely limited to the 600 V class in commercial applications. In the GaN4EmoBiL project, we demonstrated an alternative technology pathway based on GaN on insulating substrates. This enables the development of devices with blocking voltages exceeding 1,200 V. In doing so, we are laying the foundation for the future use of GaN in 800 V power electronics for electric vehicles and their system integration,” explains Junior Professor Dr. Stefan Mönch.

Mobile and cost-effective bidirectional chargers are a key component of a more flexible energy system and, at the same time, contribute to the mobility and energy transitions.