Efficient Calculation Method and Characterization of Flux Density Distribution in Nanocrystalline Core of High-Frequency Transformer Under Load Condition

Core loss is determined by flux density distribution. Since main flux density is uniform and leakage flux density is concentrated in surface ribbons of nanocrystalline core in high-frequency transformer (HFT), practical flux density in nanocrystalline core under load condition may be non-uniform. This paper proposes an efficient flux density distribution calculation method for nanocrystalline core of HFT under load condition, namely operating condition decomposition based method (OCDEM). The load condition is decomposed into open-circuit and short-circuit conditions. The practical flux density is proposed to be calculated by summation of main flux density under open-circuit excitation and leakage flux density under short-circuit excitation. Compared with time-domain FE and frequency-domain decomposition FE methods, the proposed OCDEM reduces computation time and achieves high calculation accuracy. Further, flux density distribution characteristics in nanocrystalline core are studied. Calculation results show that flux density amplitude in surface ribbons is higher than interior ribbons and that in winding end is higher than other positions. Flux density amplitude in surface ribbons increases with permeability and that in interior ribbons decrease with permeability. Finally, infrared and calorimetric measurement results show the non-uniform flux density distribution increases core temperature and loss. The obtained characteristics can guide the HFT design.