Robust converters for renewable energy generation

Inverters are particularly relevant for the grid connection of photovoltaic and wind energy systems: They ensure that energy generated from renewable sources can be fed into the grid at the correct voltage and frequency. They are exposed to particularly challenging operating and environmental conditions, which has so far resulted in relatively frequent defects and failures that lead to considerable costs for system operators.

In the "power4re" project, the Fraunhofer experts initially identified particularly relevant weak points from field data and damage analyses. Over the course of the three-year project, they determined which factors can be responsible for defects, how damage can be reliably detected and when it becomes critical for the functionality of components. The operating and environmental conditions of inverters as well as the choice of materials and the design of the respective components were taken into account.

"When optimizing inverters, it's not enough to look at the hardware and consider materials and manufacturing processes, for example. The typical application conditions - the challenges range from electrical defects such as short circuits, corrosion and moisture exposure to delamination and mechanical damage - are crucial here and require suitable test procedures," says Sandy Klengel, Manager of the "Evaluation of electronic system integration" group and head of the sub-project at the Fraunhofer IMWS.

The institute in Halle (Saale) has dedicated itself primarily to the material diagnostics of components and materials and has contributed its special expertise. That includes corrosion processes of electronic components, degradation mechanisms of insulation materials under the influence of moisture and electrical fields or the evaluation of housing materials and coatings.

During the project, the researchers at the Fraunhofer IMWS gained important new insights into the physical failure analysis of power modules in various performance classes. The focus here was particularly on moisture-related early failures (insulation damage) and long-term degradation mechanisms, for example due to the possible accumulation of elements in the silicone gel of the power modules over the operating time and a possible deterioration in corrosion resistance as a result. "Here we were able to gain important expertise in the area of optimizing the manufacturing processes and assembling the modules in the system. With this know-how, failure risks can be minimized, thus lowering maintenance costs and ultimately also reducing electricity generation costs," says Sandy Klengel.

For the analyses, unique test methods were designed or existing methods were adapted and further developed, for example to determine the moisture absorption and diffusion of ionic impurities and harmful gases in silicone gel. The characteristic data obtained was used to develop a simulation model for possible changes in the permeation properties of different coatings. It also became possible to take into account real environmental conditions such as differences between day and night and summer and winter.

"We do now have a deeper understanding of material interactions and defect formation under different operating conditions. This is an important basis for significantly improving the reliability and robustness of the components in the development of the next product generations," says Sandy Klengel. The solutions can potentially also be transferred to other fields of application in which converters are exposed to similar environmental influences, such as rail transport or electromobility.

The Fraunhofer Institutes for Wind Energy Systems IWES, for Integrated Systems and Device Technology IISB, for Solar Energy Systems ISE, for Reliability and Microintegration IZM and the Fraunhofer IMWS have pooled their expertise in the "Reliable converters for renewable energy supply (power4re)" project. They were supported by an advisory group of representatives from industrial companies.

(January 16, 2025)