Abstract
The magnetizing inductance of the medium frequency transformer (MFT) impacts the performance of the isolated dc-dc power converters. The ferrite material is considered for high power transformers but it requires an assembly of type “I” cores resulting in a multi air gap structure of the magnetic core. The authors claim that the multiple air gaps are randomly distributed and that the average air gap length is unpredictable at the industrial design stage. As a consequence, the required effective magnetic permeability and the magnetizing inductance are difficult to achieve within reasonable error margins. This article presents the measurements of the equivalent B(H) and the equivalent magnetic permeability of two three-phase MFT prototypes. The measured equivalent B(H) is used in an FEM simulation and compared against a no load test of a 100 kW isolated dc-dc converter showing a good fit within a 10% error. Further analysis leads to the demonstration that the equivalent magnetic permeability and the average air gap length are nonlinear functions of the number of air gaps. The proposed exponential scaling function enables rapid estimation of the magnetizing inductance based on the ferrite material datasheet only.
Highlights
The medium frequency transformer (MFT) is one of the key components in the isolated dc-dc converters [1,2,3,4] related to: smart grids [5], photovoltaic power plants [6], wind power plants [7], and electric vehicle charging [8,9]
The measurement of the and the equivalent permeability forsufficient two three-phase evaluating the performance of isolated dc-dc converters
This article demonstrates that the equivalent magnetic permeability and the average air gap
Summary
The medium frequency transformer (MFT) is one of the key components in the isolated dc-dc converters [1,2,3,4] related to: smart grids [5], photovoltaic power plants [6], wind power plants [7], and electric vehicle charging [8,9]. The three-phase topology is considered for high power applications where the high power density and high efficiency are required. In [10,11], an analytical approach was proposed to compare multi-phase dc-dc topologies. A 10 kVA 1 kHz three-phase MFT prototype was reported in [13], and a. 2 kVA 100 kHz three-phase MFT was reported in [14]. Cds of the MOSFET (or other power semiconductor switch). It should ensure the magnetizing current sufficient to charge and discharge the Cds during the dead time of a VSC leg. In the dual active bridge (DAB) converter [2,22], the magnetizing inductance should not increase the VSC current and it should.
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