Lagrangian Model of an Isolated DC-DC Converter With a 3-Phase Medium Frequency Transformer Accounting Magnetic Cross Saturation

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.

Modified Preisach Model of Hysteresis in Multi Air Gap Ferrite Core Medium Frequency Transformer

“…The core power loss Pc was measured in a no load test at 25°C. In this test, the MFT was supplied from a voltage source converter (VSC) operating at 20 kHz [26]. The power loss was measured with the precision power analyzer ZES Zimmer LMG670.…”

“…On the other hand, MFT modeling has to take into account the high frequency effects on the winding resistance [20], [21], parasitic capacitances [22], [23], and core loss [24], [25]. A nonlinear model of a 3-phase MFT was proposed in [26]. The precise MFT design and modeling should consider a time-dependent model of the magnetic hysteresis.…”

Equivalent converter method for analyzing complex DC–DC converting systems

“…Further development of this direction affected more complex switching electrical networks [8,9] and various types of DC-DC converters [10,11], including taking into account parasitic elements- [12]. Analysis of threephase AC-DC converters is presented in [13,14], converters with transformers in [15][16][17]. More fully, the energy functions method is used in [18], which provides also a bibliography of its development and applications.…”

Optimization of Impedance-Source Galvanically Isolated DC–DC Converters With Reduced Number of Switches

“…Provided the characteristics of ZS networks, it has widely been simulated in converters with transformers in modern power systems, such as HVDC networks, smart networks, photovoltaic power plants, wind power plants, and electric vehicle batteries. In these simulations, transformers may be integrated into isolated DC-DC power converters [6]. Therefore, an appropriate power converter is required to connect DC microgrid systems with loads [7] so that a relatively high voltage can be generated using the DC-DC converter [8], as illustrated in Fig.…”