The ReCoWind project addressed the persistent high failure rates of frequency converters in wind energy plants, which cause significant repair costs and lost generation. Field data from more than 2,700 onshore and offshore turbines, covering roughly 7,400 turbine‑years, revealed an average failure rate of 0.5 failures per turbine per year. Most of these failures occur in the phase module, comprising the IGBT modules, driver boards, and the intermediate DC‑link capacitor system. Despite advances in power electronics, the failure rate has not improved over the past decade, indicating that the dominant failure mechanisms differ from those known in other applications.

The project pursued a dual‑pronged investigation. A top‑down analysis of field data and failure reports identified moisture as a key, previously under‑studied factor. A bottom‑up approach followed, focusing on the physical and chemical degradation processes within individual components. To support this, the team developed specialized measurement techniques. In situ monitoring of wind turbine converters measured electrical operating conditions, temperature, and humidity over extended periods. Sensorised IGBT modules were installed in a high‑performance laboratory (HiPE‑LAB) to capture real‑time temperature and moisture indicators, while isolation resistance and leakage currents were recorded to assess insulation degradation.

Laboratory experiments examined moisture uptake and transport in silicone encapsulants, revealing that moisture can penetrate and accumulate within the encapsulation, leading to accelerated degradation of the semiconductor junctions. The measured moisture diffusion coefficients were incorporated into both bottom‑up and top‑down models. The bottom‑up model, based on a detailed material‑level description, predicted temperature and humidity distributions within the converter. The top‑down model, calibrated against field measurements, provided a system‑level view of operating‑point dependent environmental conditions. Comparison of the two approaches showed good agreement, validating the use of the simplified top‑down model for rapid reliability assessment.

Accelerated life testing was performed on application‑relevant components. By applying elevated temperature and humidity levels, the test duration was reduced while maintaining relevance to field conditions. The tests confirmed that moisture‑induced degradation dominates over thermomechanical fatigue in the wind turbine environment. The project also developed a methodology to extrapolate accelerated test results to real‑time life predictions, enabling more accurate reliability estimates for future converter designs.

The collaboration brought together Infineon Technologies AG, Fraunhofer IWES, and Leibniz Universität Hannover (IAL and GEM). Infineon supplied the IGBT modules and driver boards, Fraunhofer IWES led the field data analysis, modeling, and measurement development, while the university partners conducted component testing and life‑prediction studies. The project ran within the Fraunhofer Innovationscluster “Power electronics for renewable energy supply” (2014‑2017) and was funded by the cluster’s research programme. The outcomes include a set of design guidelines, accelerated testing protocols, and maintenance recommendations that collectively aim to reduce converter failure rates and improve the economic performance of wind farms.