Design of an Isolated DC/DC Topology With High Efficiency of Over 97% for EV Fast Chargers

• Published in: IEEE transactions on vehicular technology Vol. 68; no. 12; pp. 11725 - 11737
• Main Authors: Lee, Woo-Seok, Kim, Jin-Hak, Lee, Jun-Young, Lee, Il-Oun
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-12-2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Appliance industry; Batteries; Battery chargers; Buck converters; Charging; dc-to-dc converter; Efficiency; electric vehicle; Electric vehicles; Electronic equipment; Fast charger; high efficiency; High-voltage techniques; Maximum power; Passive components; Power rating; rapid charger; Rectifiers; Resonant converters; Resonant frequency; Switches; Switching; Switching frequency; Topology
• ISSN: 0018-9545; 1939-9359
• DOI: 10.1109/TVT.2019.2949080

This paper presents an DC/DC topology achieving high efficiency of over 97-% for electric vehicle (EV) fast chargers requiring a very wide output voltage range. The proposed topology consists of an unregulated resonant converter and a non-isolated buck converter. The unregulated resonant converter is responsible for the galvanic isolation for overall system, and the buck converter carries out the charging of the battery inside EV by constant-current or constant-voltage mode control. This structure provides a number of advantages such as easy realization of a very wide voltage range, no circulating-current, zero-voltage-switching operation on all the switches of the unregulated resonant converter running at high frequency and high voltage, and the achievement of high efficiency at every time over the entire battery charging profile. The availability of small passive components is a benefit because it enables the design of high power-density. In this paper, the feasibility of the proposed topology in EV fast charger applications has been verified by a prototype converter developed with the specification of 120-kHz or 50-kHz switching frequencies, maximum power rating of 20-kW, maximum charging current of 30-A, and battery voltage range of 50-650-Vdc.