Calculation of Model Based Capacitances of a Two-winding High-frequency Transformer to Predict Its Natural Resonance Frequencies

In the literature, measurement based methods are reported, which estimate the winding capacitances of a two/multi-winding transformer but offer limited application to postulate its circuit behavior in advance of prototyping. As an alternate to the experimental methods, an analytical approach is proposed in this paper. It calculates the static winding capacitances using the transformer geometry and translates them into model based quantities using an energy equivalence method. Model based capacitances are further employed to represent an equivalent π-model of a two-winding transformer. This transfer function based model permits to synthetically obtain the frequency response analysis (FRA) of a transformer, estimate its natural resonance frequencies prior to prototyping and avoid any circuit anomaly due to close proximity of resonance and switching frequencies. FEM 2D analysis and experimental measurements of a 1.5 kW, 200/100 V, 15 kHz, EE8020×2 ferrite core transformer, are furnished to validate the analytical modeling approach. The predicted and measured quantities agree well, which verifies accuracy of the proposed methodology to derive model based winding capacitances and estimate the resonance frequencies using an equivalent π-model of a two-winding transformer.