Electromobility Project DCI4Charge: Integrating Charging Infrastructure into Industrial DC Networks

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How to intelligently integrate charging infrastructure into industrial direct current networks was demonstrated by the consortium project "DCI4Charge": The batteries of electric vehicles serve as a flexible emergency reserve and help to cushion peak loads—without jeopardizing grid stability.

Energy costs remain a crucial factor in production. At the same time, the growing adoption of electric vehicles increases the number of charging points. How can this charging infrastructure now be intelligently integrated into industrial direct current (DC) networks? This was investigated by the Fraunhofer Institute for Manufacturing Engineering and Automation (IPA), the Fraunhofer Institute for Integrated Systems and Device Technology (IISB), Ambibox, Eaton, Weidmüller, the Technical University of Ostwestfalen-Lippe (TH OWL), and associated partners Bäumer, Danfoss, Maschinenfabrik Reinhausen (Germany), the University of Stuttgart (Germany), and Innelekt in the "DCI4Charge" project. A key application case within this framework is the "DC Innovation Hub" at the Weidmüller Academy in Detmold. There, a direct current network is being operated in which electricity from renewable sources is efficiently integrated into the DC network and can now also be stored and used with electric vehicles.

Increase Energy Efficiency Thanks to Direct Current

The starting point of the project was the question of how charging infrastructure can be efficiently integrated into industrial direct current (DC) networks to reduce energy costs and avoid costly grid expansion. In conventional scenarios, charging stations are supplied via the alternating current network, with each conversion step causing losses. "If we connect the charging infrastructure directly to the company's internal DC network, we can avoid these detours," explains Dietmar Hölderle, a research associate in the Industrial Microgrids research team at Fraunhofer IPA. "At the same time, we can integrate the storage capacity of vehicle batteries as a virtual battery and smooth consumption peaks."

For this purpose, the project partners developed a detailed electrical model of the DC network and the charging infrastructure, as well as a software-supported energy management system. This system takes into account not only generation and consumption but also operational constraints, such as minimum charging states. Simulations showed that secondary regulation in the DC network keeps the voltage stable, while the vehicles can simultaneously be used as a flexible battery—for example, to provide energy from the vehicle batteries during high electricity prices or to reduce peak loads.

Power Converters as the Centerpiece

To ensure that energy can flow from the DC network into the batteries as needed and flow back when required, power electronic converters form the core of the infrastructure. The Fraunhofer IISB developed galvanically isolated DC/DC converters that adjust the voltage from the industrial DC network to the level of the vehicle batteries. Unlike conventional technology, a single-stage system was implemented here. Thus, one converter stage ensures both galvanic isolation and simultaneously adjusts the network voltage to the level required by the vehicle. To achieve these hardware savings, the Fraunhofer IISB developed and implemented a sophisticated control strategy that operates stably with different vehicle classes and, therefore, a very wide voltage range.

The project partners built the DC/DC converters, measured them in the laboratory, and then tested them in an industrial direct current network. Efficiency, thermal behavior, and control performance were analyzed. The result: the converters operated dynamically, stably, achieved high efficiency, and ensured safe electrical isolation between the company network and the vehicle battery while simultaneously reducing the required components. Thus, they provide a practical foundation for a flexible DC charging infrastructure.

Virtual Batteries

At the system level, Fraunhofer IPA developed an energy management system as well as a simulation model that maps the electrical components of the DC network and enables energy-flexible operating strategies. The focus was primarily on investigating how charging and discharging strategies impact grid stability and voltage control.

The Fraunhofer IPA and the TH OWL validated the model in the laboratory: various scenarios were replicated in a test network. The DC network model demonstrated a high correlation with the measurement data from the laboratory and was successfully validated. This provides a reliable simulation model that can be used for the design, analysis, and further development of future DC networks. In parallel, the energy management system was integrated. It automates the charging and discharging processes of connected electric vehicles, taking technical and operational requirements into account. 

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