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Energies 2017, 10(10), 1462; https://doi.org/10.3390/en10101462

A High-Frequency Isolation (HFI) Charging DC Port Combining a Front-End Three-Level Converter with a Back-End LLC Resonant Converter

School of Electrical Engineering, Northeast Electric Power University, Jilin 132012, China
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Received: 21 July 2017 / Revised: 4 September 2017 / Accepted: 11 September 2017 / Published: 22 September 2017
(This article belongs to the Collection Electric and Hybrid Vehicles Collection)
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Abstract

The high-frequency isolation (HFI) charging DC port can serve as the interface between unipolar/bipolar DC buses and electric vehicles (EVs) through the two-power-stage system structure that combines the front-end three-level converter with the back-end logical link control (LLC) resonant converter. The DC output voltage can be maintained within the desired voltage range by the front-end converter. The electrical isolation can be realized by the back-end LLC converter, which has the bus converter function. According to the three-level topology, the low-voltage rating power devices can be adapted for half-voltage stress of the total DC grid, and the PWM phase-shift control can double the equivalent switching frequency to greatly reduce the filter volume. LLC resonant converters have advance characteristics of inverter-side zero-voltage-switching (ZVS) and rectifier-side zero-current switching (ZCS). In particular, it can achieve better performance under quasi-resonant frequency mode. Additionally, the magnetizing current can be modified following different DC output voltages, which have the self-adaptation ZVS condition for decreasing the circulating current. Here, the principles of the proposed topology are analyzed in detail, and the design conditions of the three-level output filter and high-frequency isolation transformer are explored. Finally, a 20 kW prototype with the 760 V input and 200–500 V output are designed and tested. The experimental results are demonstrated to verify the validity and performance of this charging DC port system structure. View Full-Text
Keywords: electric vehicle station; charging DC port; high-frequency isolation (HFI); three-level buck converter; LLC resonant converter electric vehicle station; charging DC port; high-frequency isolation (HFI); three-level buck converter; LLC resonant converter
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Cai, G.; Liu, D.; Liu, C.; Li, W.; Sun, J. A High-Frequency Isolation (HFI) Charging DC Port Combining a Front-End Three-Level Converter with a Back-End LLC Resonant Converter. Energies 2017, 10, 1462.

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