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Analysis and Design of a Multi-resonant Converter with a Wide Output Voltage Range for EV Charger Applications
Wenjin Sun, Xiang Jin, Li Zhang, Haibing Hu, and Yan Xing
Abstract This paper illustrates the analysis and design of a multi-resonant converter applied to an electric vehicle (EV) charger. Thanks to the notch resonant characteristic, the multi-resonant converter achieve soft switching and operate with a narrowed switching frequency range even with a wide output voltage range. These advantages make it suitable for battery charging applications. With two more resonant elements, the design of the chosen converter is more complex than the conventional LLC resonant converter. However, there is not a distinct design outline for the multi-resonant converters in existing articles. According to the analysis in this paper, the normalized notch frequency fr2n and the second series resonant frequency fr3n are more sensitive to the notch capacitor ratio q than the notch inductor ratio k. Then resonant capacitors should be well-designed before the other resonant elements. The peak gain of the converter depends mainly on the magnetizing inductor ratio Ln and the normalized load Q. And it requires a smaller Ln and Q to provide a sufficient voltage gain Mmax at (Vo_max, Po_max). However, the primary current increases with (LnQ)-1, and results in a low efficiency. Then a detailed design procedure for the multi-resonant converter has been provided. A 3.3kW prototype with an output voltage range of 50V to 500V dc and a peak efficiency of 97.3 % is built to verify the design and effectiveness of the converter.
Keyword DC-DC converter, multi-resonant converter, notch filter, battery charger
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