1. What are the main benefits of DC grids?
    • Resource efficiency – 50% less copper for cabling
    • Storage provides reduced downtime and increased system availability
    • Complete recovery of braking energy – no heat dissipation in braking resistors
    • Efficient integration of renewable energy
    • Lower power losses due to fewer conversion steps → increased energy efficiency
  2. What is the objective of DC-INDUSTRIE?
    In the joint project DC-INDUSTRIE, an open DC network for automated industrial plants is being developed and tested. The main areas of research are variable-speed drives, AC/DC supply devices, DC/DC converters for coupling energy storage systems or solar fields, protection and switching devices, connection technology and decentralised network management. The DC network specified in the project is:
    • open to all manufacturers and users
    • easy to use due to its logical system structure
    • energy-efficient because the entire recuperative energy is used
    • safe due to the use of fast electronic circuit breakers
    • robust due to the division into process-oriented load sectors
  3. Today industry uses 3~ AC. Why DC now?
    Many consumers already require DC voltage (DC) for their operation. For example, in frequency converters, which are required for the speed control of electric motors, AC is first converted to DC in order to generate a variable AC voltage again. DC networks have a central AC/DC conversion. The integration of renewable energies and the use of LED lighting is much easier to achieve. All decentralised AC/DC power supplies are no longer required and the resulting disturbances into the AC supply grid can be significantly reduced.
  4. Are there already functioning installations?
    Since 2018, the project partners have been developing suitable components for the model applications . These are currently running in 9 demonstration sites at BMW, Mercedes-Benz, KUKA, Homag, TH OWL, Fraunhofer IISB and Fraunhofer IPA. Measurements and tests are carried out to validate the system concept and document concrete results.
  5. What are the benefits for the plant operator?
    • reduced feedback effects into the AC grid, eliminating the need for expensive compensation systems
    • lower peak infeed power reduces energy cost all year
    • peak shaving through integration of short-term energy storage systems
    • ride-through capability during AC failure through integration of long-term energy storage systems
    • easy integration of renewable energy (solar and wind)
    • use of the entire recuperation energy
  6. What does DC-INDUSTRIE have to do with Industrie 4.0?
    In a DC network, the energy flow measurement and control are readily available. A higher-level energy management system can record all data and initiate measures for process optimisation, power distribution and avoidance of malfunction .
  7. What is the contribution of DC-INDUSTRIE to the energy transition ("Energiewende")?
    In the DC network, all recuperated energy is used and is not dissipated in braking resistors. This, together with the elimination of distributed AC/DC converters, saves primary energy. Furthermore, the DC grid allows to easily integrate energy storage systems and renewable energy generators. This is done via DC/DC converters. The AC grid is relieved of both current peaks and current harmonics.
  8. Is DC just as safe as AC?
    Yes it is. The same guidelines must be applied to the DC network as to AC networks in order to ensure human protection. For safe switching and disconnection, new semiconductor and hybrid brakers have been developed and are used in the model applications.
  9. How can system availability be increased by using the DC network?
    A frequent concern in industrial production is cost-intensive downtime due to power interruptions. The simple integration of energy storage devices into a DC network enables continued operation even during power failures.
  10. How much energy can be saved?
    It depends strongly on the application;  however, in the model applications 2-4% reduction were meassured.
  11. What distinguishes the DC-INDUSTRIE network from other DC networks, e.g. in building automation or data centres?
    • higher voltage and power range
    • highly dynamic loads
    • bi-directional power flow
    • multi-vendor DC grid
  12. What happens to three-phase motors operated directly on the grid?
    The switching device between the grid and the three-phase motor is replaced by a robust inverter (DC/AC converter) with variable speed control. This means that the motor can not only run in start/stop mode, but its speed is also optimally adapted to the process. This minimises energy consumption and power dissipation.