In this paper, design of LLC resonant DC-DC converters, which have advantages such as high efficiency, low electromagnetic interference (EMI) and high power density, is presented. An interface is designed in MATLAB using by the first harmonic approximation (FHA) analysis method to calculate circuit parameters. The accuracy of the parameters calculated by the interface is tested with simulations conducted in PLECS. Simulation results have shown that intended efficiency and zero voltage switching

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... (ZVS) are achieved over a wide load range, including low load conditions. Figure A. Circuit schema of the SST design Purpose: The main motivation of this study is to design an interface that presents the necessary parameters for the LLC resonant converter intended to be designed. The interface uses the first harmonic approximation (FHA) analysis method in calculations and aims optimal selection of quality factor ( ) and inductance ratio ( ). Theory and Methods: MATLAB is used for interface design. Firstly, the LLC resonant DC-DC converter topology has been studied, and then the first harmonic approximation (FHA) analysis method has been explained. Simulations have been conducted in PLECS and thermal modeling method has been used in order to make the efficiency calculations to represent real conditions. Results: Simulations at 3 different power levels have been conducted. The results have shown that zero voltage switching (ZVS) is achieved over a wide load range. Additionally, maximum efficiency results have been obtained between 95% and 97%. Conclusion: In this study, a LLC resonant converter design approach that aims to achieve high efficiency is discussed by using FHA analysis method. With this approach, an interface has been designed in MATLAB. The accuracy of the parameters calculated by the interface is tested with simulations conducted in PLECS. The obtained results have shown that reliable results are produced by the presented interface.