Duality-Derived Electromagnetic Modeling of an On-Board Traction Transformer Under Power-Frequency Overexcitation

Power-frequency overexcitation increases the voltage-to-frequency ratio applied to a transformer core and may drive the core into saturation, resulting in substantial distortion of the no-load current. This paper presents a duality-derived electromagnetic model for an on-board traction transformer by combining a sixth-order Foster network identified through vector fitting with a Jiles–Atherton hysteresis operator. The proposed model preserves the physical correspondence between magnetic-flux paths and equivalent-circuit elements while accounting for history-dependent core hysteresis and frequency-dependent core impedance. The model is implemented and numerically evaluated in MATLAB/Simulink R2024a, and experimental validation is performed on a 250 kVA prototype under rated power-frequency excitation and power-frequency overexcitation. Under rated excitation, the RMS relative error and NRMSE of the no-load current are 0.09% and 0.96%, respectively, with a maximum relative error of 2.90%. Under power-frequency overexcitation, the NRMSE is 4.14% and the maximum relative error is 9.37%. The results show that the proposed model accurately reproduces the nonlinear no-load current response associated with core saturation and hysteresis within the investigated power-frequency excitation range.