Abstract
Medium frequency transformers (MFTs) are a key component of DC–DC dual active bridge (DAB)-type converters. These technologies are becoming a quintessential part of renewable energy solutions, such as photovoltaic systems and wind energy power plants, as well as in modern power grid interfaces functioning as solid-state transformers in smart-grid environments. The weight and physical dimensions of an MFT are key data for the design of these devices. The size of an MFT is reduced by increasing its operating frequency. This reduction implicates higher power density through the transformer windings, as well as other design requirements distinct to those used for conventional 60/50 Hz transformers; therefore, new MFT design procedures are needed. This paper introduces a novel methodology for designing MFTs, using nanocrystalline cores, and tests it using an MFT–DAB lab prototype. Different to other MFT design procedures, this new design approach uses a modified version of the area-product technique, which consists of smartly modifying the core losses computation, and includes nanocrystalline cores. The core losses computation is supported by a full analysis of the dispersion inductance. For purposes of validation, a model MFT connected to a DAB converter is simulated in Matlab-Simulink (The MathWorks, v2014a, Mexico City, Mexico). In addition, a MFT–DAB lab prototype (1 kVA at 5 kHz) is implemented to experimentally probe further the validity of the methodology just proposed. These results demonstrate that the analytic calculations results match those obtained from simulations and lab experiments. In all cases, the efficiency of the MFT is greater than 99%.
Highlights
From the designer’s point of view, the requirement of high power density for medium frequency transformers (MFTs) is one key parameter in the process for the developing new DC–DC dual active bridge (DAB)-type converters [1,2]
To test the actual behavior of the Medium frequency transformers (MFTs) lab prototype for DC–DC converters, the MFT was connected to a DAB converter, and the effectiveness of the MFT proposed in this document was tested for the typical square voltage waves that are present in these converters
New MFT designs are key for developing new DC–DC converters for applications in mediumvoltage power grids
Summary
From the designer’s point of view, the requirement of high power density for medium frequency transformers (MFTs) is one key parameter in the process for the developing new DC–DC dual active bridge (DAB)-type converters [1,2]. The power density through the windings increases [3,4,5]. The parameters associated with power loss must be taken into consideration in the transformer design procedure [8]. The MFTs have a range of applications in DC–DC converters for smart networks [9], electric vehicles [10], wind power generators and plants [11], interfacing of photovoltaic systems [1], and solid state transformers [12,13]
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