Study on Core Loss Reduction in the Transformer of Isolated DC/DC Converter with Series L-C and Resonant L-C Shunt Filter

A medium-frequency transformer isolated DC/DC converter with series L-C and resonant L-C shunt filter is designed and simulated in this paper to eliminate high order harmonics of square wave and therefore reduce core loss of medium-frequency planar transformer. By adding an air-core series inductor with a series resonant capacitor and a resonant shunt branch consisting of another air-core inductor in series with the capacitor, specific order of harmonics can be entirely filtered without increasing extra copper loss from the inductors. At the same time the wide voltage ratio between output and input can be controlled at the first stage due to the passiveness of the inverter and rectifier. This proposed method can decrease around 5% of core loss of transformer compared with square wave and the circuit works with only 1.90% total harmonic distortion. In the meantime, it simplified the control and has the potential to operate at several hundred kilohertz to achieve compactness and miniaturization.