Mitigation of Circulating Currents in Parallel Foil Windings for Medium Frequency Transformers

The practicality of parallel foil windings assembled on medium frequency transformers (MFTs) is analyzed and experimentally verified. The efficiency improvement in case of equal current sharing in parallel windings in contrast to single foil is numerically validated. The presence of circulating currents between parallel windings is investigated using the impedance matrix of the foil windings where the impedances are numerically computed. For experimental validations, an MFT prototype with parallel foil windings is manufactured and the effect of additional external impedances on reducing the circulating currents is addressed. A simple and practical technique is proposed to ensure equal current sharing between parallel windings of MFTs coupled with series resonant converters (SRCs).