Evaluation of Core Losses in Transformers for Three-phase Multi-level DAB Converters

Paper in proceeding, 2022

This paper provides closed-form formulas for estimating the core losses of three-phase transformers excited with multi-level converters for dual active bridge (DAB) applications. The formulas are derived by applying the improved generalized Steinmetz equation with approximated flux waveforms generated from one of the windings. The effect of different winding configurations on the estimated losses is studied. The results are validated with MATLAB simulations, and their applicability for three-phase multi-level DAB converters is investigated. It is shown that for the YY and the ΔΔ configurations, an estimation error of less than 7.5% and 11.5%, respectively, can be achieved for most phase shifts between 0 and 20 degrees. It is highest when the distribution of the leakage inductance is more uniform between the primary and the secondary sides. Moreover, effect of the transition times of the bridges on the estimation error is also studied. It is established that estimating the losses from the winding, whose transition time is the largest, results in lower estimation error. It is demonstrated that using the parameters of the Δ side results in less estimation error for the YΔ and the ΔY configurations and most of the studied designs. The maximum estimation error for these two winding configurations is below 8.5% for phase shifts below 20 degrees.