Comparison Between Numerical and Analytical Methods of AC Resistance Evaluation for Medium-Frequency Transformers: Validation on a Prototype and Thermal Impact Analysis

In the future, medium-frequency transformers (with a frequency range of 5-100 kHz) will be major components in dc-dc converter applications, for both medium-voltage direct current and high-voltage direct current networks. Importantly, the corresponding power losses should be accurately calculated in order to reach performance targets (very high efficiency). This paper reviews the most known analytical models that are used to calculate the medium-frequency resistance for several winding technologies. In order to qualify these models in a future design flow, we compare the analytical model results with measurements and 3-D finite-element electromagnetic simulations and the impact on the warming. The adopted design flowchart has been tested on a 17-kHz 180-kVA prototype transformer that will be used in a dual active bridge.