A Three-Level LLC Converter With Flexible Variable-Mode Control for Wide Gain Range Application

Wide gain capability and full range efficiency are critical issues to LLC converters for wide-range applications. To address these issues, this article proposes a variable-mode controlled three-level LLC 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.

Automated summary

This article proposes a variable-mode controlled three-level LLC converter with two parallel diode-clamped legs to address the issues of wide gain capability and full range efficiency. The designed flexible variable-mode control strategy achieves soft switching and high efficiency over the wide gain range, ensuring smooth transitions among different modes and no surge current. Experimental results show that the preliminary prototype achieves full zero-voltage-switching capability and maintains high efficiency over the whole output range.