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Advanced Solid State Transformers

Periodic Reporting for period 1 - ASSTRA (Advanced Solid State Transformers)

Reporting period: 2018-01-01 to 2019-12-31

"The need for continuous and reliable energy supply and the demand to embrace the discontinuous distributed energy systems are shaping the societal challenge to migrate from the concept of existing AC grids towards the DC which would be able in a ""Smarter"" manner deal with the energy flow and integration of large numbers of renewable energy sources. In a similar way, on the side of the load, the technological development is bringing new challenges with the increasing amount of charging stations for electrical vehicles and heavily fluctuating load profiles of data centers. The unit that enables and adapts the energy flow from and to a load or energy source is the transformer. In a DC grid, additional power processing units are necessary to consider in order to make the transformer functional, in this case, the transformer, or together with the power processing unit – solid-state transformer (SST), works at considerably higher frequencies (medium-range) than traditional 50 Hz.
The research on the medium frequency transformers (MFT) for SSTs (grid applications) is going on. The application of the MFTs would reduce dramatically the sizes of the transformers due to the rise of the operating frequency, and respectively the use of active materials like copper, ferrites and insulation materials. The technical challenge is to focus on the new design principles of the insulation materials, that would be able to deal with the DC excitation and confront the high level of stress generated by both electrical and thermal domain. The choice of the design method is a fundamental objective to define and predict the MFT performance. Specifically, facing the fast switching frequency of the emerging wideband gap switches. The consequences of newly developed switches play the crucial role of the life-time and fault-tolerance of the MFT."
In the frame of the technological challenge and the research objectives, the first prototype of MFT is being built. The proof of concept prototype should give insights into the high switching frequency effects on the transformer windings and insulation. At the same time, the mathematical models are defined to predict these effects. The results based on the validation of the measurements and mathematical models have been submitted to an international conference and a deriving journal publication is in progress.
The current work in progress is expected to contribute to the main challenge of migration from AC to DC excited energy distribution systems. The physical understanding of the charge and stress distribution inside MFTs would lead to novel physical models which, implemented in numerical platforms would improve the prediction of the lifetime and performance of the MFT.
Components of the MFT prototype before assembly
CAD drawings for the MFT