Magnetic Equivalent Circuit of MF Transformers: Modeling and Parameter Uncertainties

Abstract

Medium-frequency (MF) transformers are extensively used in power electronic converters. Accordingly, accurate models of such devices are required, especially for the magnetic equivalent circuit. Literature documents many different methods to calculate the magnetizing and leakage inductances of transformers, where, however, few comparisons exist between the methods. Furthermore, the impact of underlying hypotheses and parameter uncertainties is usually neglected. This paper analyzes nine different models, ranging from simple analytical expressions to 3D detailed numerical simulations. The accuracy of the different methods is assessed by means of Monte Carlo simulations and linearized statistical models. The experimental results, conducted with a 100kHz/20kW MF transformer employed in a 400V DC distribution system isolation, are in agreement with the simulations (below 14% inaccuracy for all the considered methods). It is concluded that, considering typical tolerances, analytical models are accurate enough for most applications and that the tolerance analysis can be conducted with linearized models.