Synthesis of an Equivalent π-model of Two-winding Transformer and Resonance Frequency Estimation Using Lumped Circuit Parameters

In literature, experiment based methods are met, which postulates circuit behavior of a two-winding transformer using empirical formulae based on impedance measurement and parameter extraction. Alternately in this paper, an equivalent π-model of a two-winding transformer is derived using circuit synthesis method. Individual branch impedances of π-model are expressed using the lumped circuit parameters, which conserve the intertwined effects among the transformer parasitics over a wide frequency range. Proposed π-model permits to find the open-circuit and short-circuit impedances of transformer and forecast its parallel and serial resonance frequencies. Any anomaly, e.g. close proximity of the resonance and switching frequencies, can be avoided prior to transformer prototyping, saving time, effort and cost. Accuracy of the proposed π-model is verified with the help of an exact circuit of a two-winding transformer, modeled in MATLAB. Performance of the equivalent π-model is further validated experimentally using frequency response analysis (FRA) of a 1.5 kW, 200/100 V, 15 kHz, EE8020×2 ferrite core transformer. Close agreement is noted among analytical, simulation and experimental results, which substantiates accuracy of the proposed π-model and its utility for transformer designs at medium/high frequency.