Fixed-Frequency Phase-Shift Modulated Capacitor-Clamped LLC Resonant Converter for EV Charging

Abstract

LLC resonant converter has been widely employed in electric vehicle (EV) charging applications. However, conventional frequency-modulated LLC converters generally demand a wide frequency variation range and are difficult to scale up, while the traditional phase-shifted (PS) LLC converters have the issues of ease of losing soft-switching condition and high turn-off current. In response to these challenges, this article proposes a new method for EV charging applications based on the capacitor-clamped LLC converter topology and fixed-frequency PS modulation. Compared with traditional PS LLC converters, the proposed method can achieve 1) smaller phase shift variation range, 2) lower turn-off current, and 3) wider soft switching range, resulting in higher efficiency. An 825-W prototype with 200 V input and 125-210 V output range verified the features of the proposed idea, and the efficiency reaches 97.82% at the maximum output power.