Wideband Transformer Modeling Including Core Nonlinear Effects

Wideband, black-box transformer models can be obtained via frequency sweep measurements on transformer terminals followed by rational model extraction via passive curve fitting. However, these models do not include core nonlinearity effects. A modeling approach is introduced where a wideband linear model is connected in parallel with a nonlinear 50/60 Hz model using filters. The filters are used to ensure a smooth transition from the 50/60 Hz model to the wideband 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 wideband model.