High-frequency transformer design for the soft-switching solid state transformer (S4T)

High-frequency transformer is a key element of the solid state transformer. The high-frequency transformer for a patent-pending topology - soft-switching solid state transformer (S4T) - has a unique feature of DC biased flux. This paper first evaluates the high-frequency transformer design using different high-frequency magnetic materials. Then a new hybrid transformer design methodology, which incorporates magnetic cores and permanent magnets, is also proposed. The permanent magnets provide pre-biased flux for the magnetics such that the usable B-H curve range is extended. Finite element analysis simulation and experimental verification show that the hybrid design can save magnetic materials by more than 50%.