Protection concept for renewable energies: New solutions for safe IGBT/SiC inverters

When failures occur in the power distribution of modern energy systems, high short-circuit currents are generated, producing large amounts of energy at the failure location. In such cases, shutdown devices are installed to ensure that the overcurrent is interrupted and the systems are thus protected. However, the solutions available today are designed for conventional power generation plants and require a shutdown time of up to 100 milliseconds.

This is too long for the renewable energy sector, where semiconductor-based inverters are often used as an interface to the grid. IGBT modules, which integrate several chips in an insulated housing to efficiently switch high voltages and currents, are particularly common. The high power densities that can be achieved with this compact design are further increased by the use of silicon carbide (SiC) as a material for semiconductor components. As a result, some inverter configurations are no longer adequately protected by conventional overcurrent devices. The free-wheeling diode chips of IGBT modules are particularly affected by this problem, as they cannot actively stop the flow of current in the event of impermissible short-circuit currents. This can lead to an explosion of the semiconductor modules, followed by plasma leaks, which can trigger additional short circuits in other components of the overall system.

To develop a solution to this problem, Infineon Bipolar GmbH, Dresden University of Technology, and Fraunhofer IMWS collaborated on the recently completed "GreenGridGuard" project. "We investigated the material behavior and protective effect of novel semiconductors and, at the same time, developed solutions for generating a targeted short circuit very quickly and permanently in the event of a failure using a combination of circuit breakers and semiconductors. This ensures that the inverter switches off, thus protecting the other components from overcurrent," says Carola Klute, who led the sub-project "Material Diagnostics and Reliability Analysis" at Fraunhofer IMWS. "This is an important basis for new power electronics solutions that enable improved grid connection of renewable energies."

The short circuit, which is generated in less than 1 millisecond, remains permanently in place during the failure ("short on fail" guarantee). At the same time, solutions were found to prevent the housing from breaking even under very high loads, so that no plasma can escape from the inverter.

Fraunhofer IMWS contributed its expertise in material diagnostic analyses of semiconductor components before and after electrical stress to the project. Methods such as non-destructive failure localization (optical inspection, X-ray analysis, ultrasonic microscopy), material-selective preparation (cross-section preparation), and powerful microstructural analysis (scanning electron microscopy SEM, material analysis with energy-dispersive X-ray spectroscopy EDX) were used.

"In the project, we were able to develop a precise understanding of the microstructural and mechanical mechanisms at work in the components and systems to be used. We were also able to contribute our expertise in the individual development of micro-scale testing methods for different material systems and for the evaluation of thermomechanical stresses," says Klute. For example, suitable diagnostic methods and reliability tests were developed for the new shutdown device and recorded in a catalog. One focus was on researching material reactions in the event of an accident and evaluating how these affect reliability.

In order to develop the most effective protection system possible, the project partners relied on various demonstrator design variants, which were tested and evaluated during the two-year project period. A chip design with a fixed connection between a thick carrier disc on the anode side and a loosely fitting contact disc on the cathode side proved to be particularly effective. This variant was then further developed to optimize the component in terms of short-circuit effect.

The combination of methods available at Fraunhofer IMWS allowed insights into destroyed layer systems, melting, cracks in silicon, phase formation, fracture patterns in the ceramic housing, the formation of island areas, and the diffusion of material from the defect site into the silicon during the evaluation of the individual variants. This provided evidence that even under high surge current loads (between 20 kA and 100 kA), damage to the component is limited to the areas of the electrical and mechanical predetermined breaking point – thus achieving the desired protective effect.

(October 23, 2025)