18.03.2022

Direct current technology - a building block of future electricity grids

The growing grid load and the volatility of renewable energy plants pose new challenges for the power grid. Once the optimization potential of the power grid has been exhausted, grid expansion becomes necessary. In this context, direct current (DC) technology is of particular importance.

DC technology increases the efficiency of electrical grids and is thus an important component in successfully meeting the challenges of the energy transition. Depending on their design, DC grids are almost completely controllable, low-loss and resource-efficient. While the HVDC point-to-point connections for the north-south exchange of high power are currently being built in Germany, the Thuringian Energy Research Institute (ThEFI) at the TU Ilmenau is already researching solutions for the complex issues associated with the expansion of future, more efficient power grids.

 
Research on efficient, safe direct current networks
Portrait Prof. Dr. Dirk Westermann, Direktor des ThEFI der TU IlmenauTU Ilmenau/ThEFI
Prof. Dr. Dirk Westermann, Director of the ThEFI at TU Ilmenau

As part of the "OVANET" project, ThEFI scientists are investigating, for example, how the protection of DC systems can be ensured. "DC networks exhibit different fault behavior than classic three-phase networks," explains the director of ThEFI, Prof. Dr. Dirk Westermann. "We are therefore researching solutions specifically tailored to DC grids to ensure efficient, resource-saving and fail-safe utilization of such grids." In order to handle faults in the DC grid as safely and efficiently as possible, the Ilmenau experts and their project partners are deriving planning criteria for establishing protection zones, developing procedures for fault location and defining fault explanation sequences. At the same time, they are investigating how the developed procedures for so-called curative grid security, i.e. the efficient handling of faults in the DC grid, can be integrated into the system. In doing so, the researchers are not relying on maintaining redundant operating resources, i.e., systems in which in which each unit can perform the task on its own if the other unit fails, Instead, they are relying on the significantly faster response capability of converters that can actively return the grid to permissible operation within milliseconds in the event of a fault.

   
MVDC technology for power flow control
TU Ilmenau/ThEFI
The Dynamic Network Control Centre at the ThEFI of the TU Ilmenau

In the already completed project "VNB-DC", the use of DC technology in the distribution grid was investigated under the leadership of the TU Ilmenau. The aim of the research work was the coupling of the 110 kV levels from Saxony-Anhalt via Thuringia to Bavaria by means of MVDC technology (medium voltage direct current technology). MVDC technology enables the interconnection of different grids in the first place and offers a very high controllability. This means that in addition to the temporal shifting of power and the sectoral shifting, the controllable regional shifting of power has also been introduced. Prof. Westermann: "This means that surpluses from renewable energies can not only be stored to be used at any time or called up for different conversions, for example into fuels or electrical energy, but in the future surplus energy can also be made available within the interconnected states according to demand." The researchers thus demonstrated that MVDC plants make it possible to redirect power flows in a targeted manner in order to respond to bottlenecks as they occur. In the future, this may significantly reduce the need to shut down power plants to relieve load on the grid. In addition, the distribution grids can exchange power directly with each other and thus relieve the transmission grid, which currently ensures this exchange.

 
Important building block of future energy systems
Monitore zur Überwachung der NetzleitwarteTU Ilmenau/ThEFI
The Dynamic Network Control Centre at the ThEFI of the TU Ilmenau

DC technology has now reached every voltage level and is regarded internationally as an important building block of future energy systems. Although the use of DC technology often still requires a certain amount of research, it opens up promising opportunities to increase both operational efficiency and cost-effectiveness as well as resource and area efficiency, and thus the ecological justifiability of energy systems.
 

High degree of digitization

In order to be able to achieve a high degree of automation of electrical grids, advanced digitization in the field of electrical power systems is essential, in addition to the use of flexible technologies such as DC technology. Measured data must be synchronized and transmitted to the control centers at periodic intervals of a few milliseconds so that they can ideally be processed fully automatically in corresponding assistance systems. In many applications, DC systems are also designed to work across network operators, so that automatic standardized communication between the control centers may also be necessary. Furthermore, the new degrees of freedom provided by DC technology can only be used if extensive optimization and variant calculations have been carried out beforehand using quasi-stationary and dynamic models.

These processes are very complex and require a high degree of computing power, for which an excellent infrastructure is available at the TU Ilmenau in addition to internationally recognized high research competence.

 

Contact

Univ.-Prof. Dr.-Ing. Dirk Westermann

TU Ilmenau, Director Thuringian Energy Research Institute ThEFI
+49 3677 69-2838
dirk.westermann@tu-ilmenau.de

   
The ThEFI of the TU Ilmenau

The Thuringian Energy Research Institute ThEFI unites 13 disciplines from four faculties of the TU Ilmenau in the spirit of interdisciplinary research. The focus of the work is on the transfer of knowledge and the further development of research competence in all areas of energy, environmental and systems engineering and the cooperation with scientific partners. The areas of activity of ThEFI include the research and development of processes related to energy as well as the corresponding marketing of research results in cooperation with industrial companies and associations.