DC Grids

The massive expansion of renewable energy sources will involve a wealth of change in electrical energy supply. An important aspect arises out of the transition from a centralized to a highly decentralized supply system.

For reducing system costs and achieving highest efficiency in providing electric energy, DC based systems and grids will play key roles in the future. This is due to the intrinsic DC characteristic of the main elements, like photo­voltaic generators and electrical energy storages, and the elimination of many inefficient DC-to-AC and AC-to-DC conversion steps in the case of direct supply of the large number of electronic loads.


IISB Insights - DC Grids

Local and decentralized controlled DC grids offer many advantages compared to the conventional public AC grid. Bernd Wunder, Group Manager DC Grids, gives an introduction into our various DC activities.

© Fraunhofer IISB

We at Fraunhofer IISB are happy to support you with power electronics, protection technology, grid analysis and stability for DC applications.

DC Grids with Bidirectional Charging Technology for Electric Vehicles

»eMobiGrid« Joint Project 

The project partners in eMobiGrid are working on a comprehensive energy infrastructure that supports the efficient integration of sustainable energy sources and facilitates the further development of electromobility. As a solution, the focus in eMobiGrid is on local and decentralized DC grids. These enable low-loss coupling of renewable energy sources and battery storage and are suitable for the integration of charging stations for different types of electric vehicles. The key components within these DC grids are efficient, reliable and safe DC/DC converters.

In eMobiGrid, the DC Grids group at the IISB is developing a particularly flexible, insulating DC/DC converter. Due to its ultra-wide voltage range, this converter is specifically optimized for bidirectional DC charging. This means that, in addition to passenger cars, commercial vehicles can also be charged and discharged. Bidirectional charging allows the batteries of electric vehicles to be used as intermediate storage in the DC grid. In this way, they buffer the overproduction of renewable energies. The bidirectional charging technology is therefore particularly important for grid stability when the energy supply fluctuates

Project Partners: Richter R&W Steuerungstechnik GmbH, eCharge Hardy Barth GmbH, EnQs gmbH, Lehrstuhl Mess- und Regeltechnik (MRT) (University Bayreuth)

Funding: eMobiGrid is funded by the German Federal Ministry for Digital and Transport (BMDV) within the framework of the "BMDV Electric Mobility Funding Guideline" with approximately three million euros. The funding program is coordinated by NOW GmbH and implemented by Projektträger Jülich (PtJ).

Press Release: Published on 17/05/2023 in German

R&D Topics

Our Focus

  • Highly efficient and cost-effective DC/DC converters
  • Increasing energy efficiency through DC grids, from home and office to commercial buildings
  • Innovative solutions for DC connectors, switches, and protection elements
  • Control strategies for converter-based DC-grids incl. grid stability analysis and error control
  • Evaluation of new elements based on SiC or GaN for faster switching and increased efficiency, especially under light load conditions
  • Packaging with low parasitic inductance and new circuit topologies to benefit from faster switching
  • Solutions for soft migration of energy- and cost-efficient DC-applications into existing AC installations
  • Profiles of power sources and loads to simulate or characterize grid components and systems
  • DC charging technologies for electro mobility and smart grid

Products & Services

Development of DC grid components

  • DC distribution solutions for home and office applications
  • Safety, protection, and switching elements
  • DC grid monitoring systems
  • DC lighting
  • Energy storage systems

Customized Converters

  • DC/DC converters for all kind of energy management tasks
  • For single and bipolar DC grids (e.g., +/-380 V three wire grid)
  • Up to 200 kW per power channel
  • Standard max. voltages 430 V and 850 V (higher voltages on request)
  • Low DC link capacitance versions for lowest fault energies
  • User configurable sink/source operation with current a/o voltage control, individual current limiting and short circuit characteristics, higher level control functions like MPP tracking or battery charging.
  • High control dynamics for fast error-control and special safety and protection  functions (e.g., arc-blanking)  
  • Innovative droop control for realization of smart grid functionalities without an overlaid high-speed data link between the grid components
  • Isolating bidirectional AC/DC converters for the coupling of AC and DC grids

System Evaluation

Characterisation and testing of all kind of DC-Grid components up to 1500 VDC

Integration into smart building concepts

Stability analysis from single components to complete DC grids

© Fraunhofer IISB
© Fraunhofer IISB

Application Center for DC Grid Technologies

The Fraunhofer IISB office and lab building is already equipped with a DC grid system. We steadily increase and optimize this DC application platform to achieve a maximum in efficiency, functionality, and user comfort.

All necessary key components are developed at Fraunhofer IISB together with our industrial partners. Examples are a battery storage system, different DC/DC and AC/DC converters, a DC Grid Manager for controlling the energy flow, and several safety components for typical DC grids in 380 VDC or ±380 VDC configurations. A proprietary DC fast charging solution allows the cost effective realization of e-car charging stations.

This unique platform is open also for our industrial partners and offers:

  • Application-oriented testing of DC micro and nano grid components
  • Data acquisition under realistic operational con­di­tions
  • Optimization of the energy flow between different sources, loads, and energy storage devices; evaluation of control strategies
  • Education and advanced trainings in the field of next generation power supply and local grid technologies