Hybrid Variable Frequency LLC Resonant Converter With Wide Output Voltage Range

This article proposes a multimode hybrid LLC resonant converter with wide output voltage range. Without auxiliary switches, the converter can operate in three different modes by controlling the drive signals of the primary switches: low-gain mode, medium-gain mode, and high-gain mode. Variable frequency modulation is adopted in each operation mode, and an ultra-wide output voltage range can be achieved with smooth mode transition in the proposed converter. The characteristic circuit structure allows the converter to maintain a wide voltage gain range even though magnetizing inductance is designed to be larger. In addition, zero-voltage switching of the primary side mosfet s can be realized due to the operation region above resonant frequency and justified parameter design in whole voltage range. Finally, a 3.3-kW prototype with 60–420 V output voltage is built to verify the effectiveness of the proposed converter. The prototype achieves 97.5% peak efficiency and demonstrates good efficiency performance over an ultra-wide output voltage range.