Fraunhofer Institute for Transportation and Infrastructure Systems IVIThe electrification of heavy-duty and passenger transport is a key component of the transportation transition. However, the availability of suitable charging infrastructure poses a major challenge, particularly for trucks and buses: Large battery capacities require megawatt-level charging power to achieve practical charging times. With the successful completion of the collaborative "HV-MELA-BAT" project, a complete high-voltage megawatt charging system is now available that meets these requirements—while setting new standards in contact technology engineering. In the project, Fraunhofer IVI developed a high-performance charging interface that utilizes innovative face-contact technology, thereby outperforming previous systems. The project was coordinated by the Fraunhofer Institute for Solar Energy Systems ISE; other partners included Motion Control & Power Electronics GmbH, STS Spezial-Transformatoren Stockach GmbH, and Mercedes-Benz Energy GmbH.
Safe transmission of high currents
In systems with charging capacities of up to two megawatts, both very high currents and voltages of 1,250 volts must be transmitted safely and reliably. Conventional contacting systems quickly reach their limits in this context. Therefore, Fraunhofer IVI focused their work on developing a charging interface that meets these extreme requirements while remaining practical in everyday use.
The solution: a semi-automatic system with internal contact coupling that uses innovative end-face contact technology. This technology enables particularly safe and efficient power transmission at high power levels. The plugging process is supported by a handling aid that guides the heavy charging cable and facilitates operation.
Face-contact coupling as a first
"By the end of the project, our development was able to outperform even those systems that are already available on the market. The face contact in the charging plug, in particular, is a true first—we aree very proud of that as a team," explains Tim Vorwerk, project manager within the Charging Infrastructure Team at Fraunhofer IVI. Practical tests have demonstrated that the system reliably transmits charging power of up to 2 MW at 1,250 V. The use of this contact coupling technology in a charging plug represents a technological novelty and underscores the innovative nature of the development work carried out.
Efficient comprehensive system with buffer storage
As part of the project, a comprehensive charging system was developed in accordance with the new Megawatt Charging System (MCS) standard, which is also downward-compatible with the previous CCS standard. Fraunhofer ISE developed highly efficient power electronic converters for this purpose: The galvanically isolated DC/DC converter achieves a volumetric power density of 9 kW/l at a clock frequency of up to 200 kHz, with a record-breaking efficiency of 99.26 percent.
An integrated buffer storage system made from second-life car batteries enables full charging power even at limited capacity grid connection points. The system was designed so that it can provide an additional 500 kW with a 500 kW grid connection. During the demonstration at the Fraunhofer ISE multi-megawatt laboratory in Freiburg in July 2025, the entire system demonstrated above-average efficiency from the AC grid to the vehicle battery.
Shaping the charging infrastructure of the future together
Close collaboration among the project partners made it possible to optimally harmonize all components—from power electronics and contact technology to energy management. The result is a future-proof charging system that makes a significant contribution to the electrification of heavy-duty transport, thus advancing the transportation and energy transition.
The "HV-MELA-BAT" project was funded by the German Federal Ministry for Economic Affairs and Energy.
