A Three-Level <i>LLC</i> Converter With Flexible Variable-Mode Control for Wide Gain Range Application
Hao Tong, Zheyu Miao, Huipin Lin, Wenxi Yao, Wuhua Li, Zhengyu Lü
Abstract
Wide gain capability and full range efficiency are critical issues to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters for wide-range applications. To address these issues, this article proposes a variable-mode controlled three-level <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter with two parallel diode-clamped legs. The proposed converter has four operation modes with different voltage gains, including the traditional frequency control mode and three new operation modes. With a deep analysis into the voltage gain and soft-switching characteristics of each operation mode, the designed flexible variable-mode control strategy can achieve soft switching and high efficiency over the wide gain range. Furthermore, it ensures smooth transitions among different modes and no surge current in the entire operating range. The effectiveness of the proposed method is investigated by a 400 V input, 8–65 V/1.5 kW output prototype. Experimental results show that the preliminary prototype achieves full zero-voltage-switching capability and maintains high efficiency over the whole output range.