Accurate calculation of leakage inductance for balanced and fractional-interleaved winding in medium-frequency high-power transformer

A medium/high-power conversion system using power electronic (PE) converter along with a medium/high-frequency transformer, offers many desirable features that are beneficial for present-day power system topologies. Leakage inductance is identified to be one of the key parameters to characterize performances of such a medium-frequency (MF) high-power (HP) transformer. In this paper, existing analytical method to calculate leakage inductance of a concentric winding is further refined employing mean turn length of individual layer and winding porosity factor. Impact of interleaving to reduce leakage inductance is studied. Consequently different winding dispositions (normal and interleaved) and conductor geometries (foil, round) are investigated for a 10 kW, 0.5/2.5 kV, 1 kHz transformer design. Finally generalized method to deduce leakage inductance of fractional-interleaved winding is introduced in scope of this paper. Analytical calculations are corroborated with PEMag simulation results. With proper selection of wire and core geometry, good agreement between analytical and PEMag results is achieved at medium switching frequency, which substantiates aptness of presented methodology.