An Improved LLC Resonant Converter With Reconfigurable Hybrid Voltage Multiplier and PWM-Plus-PFM Hybrid Control for Wide Output Range Applications

This paper proposes an improved LLC resonant converter with reconfigurable hybrid voltage multiplier for wide output voltage range applications. By adopting three legs and two active switches, the rectifier can be reconfigured to three configurations, i.e., full-bridge rectifier, hybrid voltage-multiplier rectifier and voltage-multiplier rectifier, covering the range of more than three times of the minimum output voltage. Compared with conventional LLC converter, the operating range of each configuration is narrowed so that the magnetizing inductance is optimized and switching frequency range is narrowed to achieve higher efficiency. Pulsewidth plus pulse-frequency modulation strategy is employed to achieve smooth transition between these operation modes. Zero-voltage switching of all power MOSFETs and zero-current switching of all secondary-side diodes are achieved as well. Detailed operational principles, characteristics, design consideration, and control stagey of the proposed converter are analyzed. A 3.3 kW 150-450 V output prototype is built and tested to verify the effectiveness and advantages of the proposed converter.