Determining Magnetically Nonlinear Characteristics of Transformers and Iron Core Inductors by Differential Evolution

This paper deals with the differential evolution (DE)-based method for determining the magnetically nonlinear iron core characteristics of transformers and iron core inductors. The unknown iron core characteristic, approximated by the sum of exponential functions, is included in a dynamic model of the tested device. The approximation function parameters are determined by DE. The optimization objective is the best possible agreement between the measured and the dynamic model calculated currents in the time and frequency domains. Using the measured inrush currents and corresponding voltages, the magnetically nonlinear characteristic can be determined over a broad operational range. The inclusion of iron core characteristic, as determined by the proposed method, in the transformer dynamic model gives very good agreement between the measured and calculated currents in both transient and steady states.