LAUSR

The operational frequency of a transformer is an important factor in the configuration of an isolated DC-DC converter. However, discussions regarding this frequency are inadequate. This study focuses on the frequency characteristics of the transformer. The authors obtained the frequency characteristics of the impedance and the loss of the transformer to explain its fundamental attributes. When the transformer is employed for a power electronic transformer (PET), the waveform of voltage is rectangular. The loss under this waveform was obtained to observe its characteristics. Further, the issues with the isolated DC-DC converter are explained. The natural frequency, composed of leakage-inductance and equivalent-parallel-capacitance, determines the performance of the isolated DC-DC converter. When the operational frequency of the isolated DC-DC converter is below its natural frequency, the loss increases under no-load or light-load conditions. This increase in the loss is caused by the current, which contains the natural frequency of the transformer due to the ringing.