The energy supply in Germany and Europe is undergoing fundamental changes: More and more electricity comes from solar and wind power and is stored in batteries or other storage systems. To use this electricity efficiently and reliably-for example, in factories or AI data centers-modern grids are increasingly relying on direct current (DC) instead of alternating current (AC).
This is because many generators-such as photovoltaic systems-as well as consumers and battery storage systems naturally supply, use, or store direct current. As a result, there are no losses from converting AC to DC.
Particularly in low-voltage grids up to 1,500 V, this is leading to the emergence of an increasing number of self-sufficient DC island grids, known as microgrids-that is, autonomous systems independent of the public power grid. To ensure that such DC grids can be operated safely and stably even for high-power applications-such as megawatt-scale charging of electric vehicles or large ground-mounted photovoltaic systems-and can be integrated into the overall energy system, novel switching and protection device concepts are necessary.
In the HybSchaDC2 project, a total of 15 partners from academia and industry are therefore developing hybrid and purely power-electronic switching and protection devices. These switches are designed to reliably handle currents up to 3.5 kA (kiloamperes) and voltages up to 1.5 kV (kilovolts) and protect low-voltage networks from short circuits and overloads - while maintaining selectivity. This means that only the fault is isolated, while all’other parts of the system not directly affected by the fault remain operational. This is made possible by switching and protection devices that trip specifically in the event of a fault, thereby increasing the supply reliability, stability, and resilience of the entire system.
"In addition to equipment protection, personal safety is of crucial importance in low-voltage systems," explains Prof. Frank Berger, subproject lead and head of the Electrical Switchgear, Components and Systems Engineering Group at TU Ilmenau. According to the scientist, this is particularly challenging:
In modern DC grids, the fault current rises significantly faster than in conventional AC grids. Our circuit breakers must therefore react extremely quickly. This means that in the future, the fault current must be interrupted within a few hundred microseconds (µs) to 1 millisecond (ms).
Prof. Berger and his team are convinced: The innovative hybrid switching devices and so-called Semiconductor Circuit Breakers (SCCBs) being developed in
These hybrid switching devices consist of three subsystems: a mechanical contact system for conducting current, fast power semiconductors for ultra-fast current interruption, and surge protection to shield the power electronics from excessive voltages caused by the rapid switching operations. In SCCBs, the mechanical contact system is omitted, while the power electronic switching element and the overvoltage protection are also included here. Depending on the application, different components are to be used and tested: "For SCCBs, depending on the application, we will use IGBTs or MOSFETs, but also test new JFETs."
However, this initially presents the scientists with a number of challenges: "The switching processes in hybrid devices are efficient, but also very complex," explains Prof. Berger. His team is therefore first using models and simulations to investigate how the individual components interact in order to achieve the best possible switching behavior. They then verify the results through extensive experiments with demonstrators and model switches.
The focus is on key questions: How do the switches behave in different grid situations? What influence do magnetic fields and new switching gases have on arc quenching? How can silver-based contact materials be used in the most resource-efficient way possible? And how can sustainable materials and recyclable switching chambers help make switching devices more resource-efficient and environmentally friendly overall?
Together with This results in monitoring systems capable of monitoring both the condition of the switches and the stability of the entire grid.
The consortium of research and industry, which includes Panasonic Industry Europe, the TU Ilmenau, Phoenix Contact, Infineon, Future Systems, Elektrotechnische Apparate (E-T-A), Doepke Schaltgeräte, Stercom Power Solutions, Schaltbau, Heraeus Precious Metals, the Fraunhofer Institute for Integrated Systems and Device Technology (IISB), Gustav Klein, Richter R+W, TEAG, and ECPE, has already worked together successfully for the most part in the predecessor project HybschaDC.
The demonstrators developed in the new project are to be tested as smart grid nodes in various low-voltage DC systems, for example in high-power industrial distribution systems, megawatt charging parks, and battery storage systems for grid support. Prof. Berger:
Our common goal is to use electricity from renewable sources efficiently, operate microgrids and charging infrastructure stably, and supply industrial and residential areas safely, flexibly, and sustainably.