Abstract
This article presents a nonlinear equivalent circuit model of an isolated dc-dc converter with a 3-phase medium frequency transformer. The model takes into account the magnetic cross saturation of the 3-phase core-type magnetic circuit. The model is suitable in detailed electromagnetic transient simulations of power systems involving isolated dc-dc converters. The model is developed using the Lagrange energy method. It involves a matrix of dynamic inductances containing a nonlinear term resulting from core magnetization and a linear term resulting from leakage flux. The model parameters are determined based on a series of magnetostatic finite element method simulations. This approach is convenient when applied to high power transformers offering a limited characterization effort, or if the transformer prototype does not exist. The experimental validation performed on a novel 3-phase MFT prototype in a 100 kW 1.2 kV 20 kHz dual active bridge converter has proved the validity of the model and model parameters. The no-load steady-state and inrush tests and the full-load test show a very good fit between the simulated and experimentally measured waveforms. The comparison with a classical simplified model neglecting magnetic cross saturation shows a significant difference in the no-load inrush test.
Highlights
T RANSFORMER modelling has been extensively studied for electromagnetic transient simulations of power systems
In modern power systems: HVDC grids, smart grids, photovoltaic power plants, wind power plants, and electric vehicle charging, the transformer may be a component of isolated dc-dc power converters [1]–[5]
The distributed parameter models are used in the analysis of electromagnetic wave propagation based on the transmission line theory. These models are usually used in the analysis of electric devices at high frequency or in the analysis of large power systems
Summary
T RANSFORMER modelling has been extensively studied for electromagnetic transient simulations of power systems. The distributed parameter models are used in the analysis of electromagnetic wave propagation based on the transmission line theory These models are usually used in the analysis of electric devices at high frequency or in the analysis of large power systems. A hybrid model based on lumped electric and magnetic parameters suitable in electromagnetic transient simulation was proposed in [21] and [22]. The authors of [34] claim that their model is superior when compared to a classical nonlinear model based on three single-phase transformers and neglecting magnetic cross saturation, since it allows to analyze precisely the transformer inrush and fault conditions. This article proposes an equivalent circuit model of an isolated dc-dc converter with a 3-phase medium frequency transformer (MFT).
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