Wide-Band Transformer Modeling Including Core Non-Linear Effects

Abstract

Wide-band, black-box transformer models can be obtained via frequency sweep measurements on transformer terminals followed by rational model extraction via passive curve fitting. These models do however not include core non-linearity effects. A modeling approach is introduced where a wide-band linear model is connected in parallel with a non-linear 50/60 Hz model using filters. The filters are used to ensure a smooth transition from the 50/60 Hz model to the wide-band model with increasing frequency. Model stability is ensured by enforcing passivity for all possible states defined by a piecewise-linear representation of the magnetizing inductance. This hybrid modeling approach is demonstrated for the modeling of a single-phase transformer representing the alpha-mode of a three-phase two-winding transformer. The model is shown to correctly reproduce inrush currents and short circuit currents predicted by the 50/60 Hz model, and high-frequency transferred voltages predicted by the wide-band model.