Gapless Transformer Design by Using Nanocrystalline Flake Ribbon

Air gaps are essential to avoid core saturation in power magnetic components. However, discrete air gaps cause a more severe fringing effect which increases winding and core losses. Gapless design is difficult in high-power applications due to the limitation of materials with suitable electromagnetic properties. In this article, an emerging nanocrystalline flake ribbon (NFR) has been used to form gapless magnetic cores for high-frequency transformers. Loss reduction of the entire transformer has been achieved without the discrete air gaps. The power density of the transformer is competitive due to the suitable permeability and saturation point of NFR at high frequencies (hundreds kHz). The core losses are separated and compared with its precursor conventional nanocrystalline ribbon. Comparison to two other transformers using ferrite and nanocrystalline materials has been carried out in a 5.5 kW, 100 kHz dual active bridge (DAB) converter. The transformer using the NFR core shows the highest efficiency. The NFR transformer exhibits 33.2% and 67.1% winding loss reduction compared to the ferrite and the nanocrystalline transformer, respectively. Error analysis has shown the loss measurement error is within 6.1%.