Fixed-frequency PWM LLC resonant converter with 8-type rectifier for wide input voltage applications

This paper proposes a fixed-frequency PWM modulation for LLC resonant converter with an 8-type rectifier unit in the shape of a number 8. By controlling the duty cycle of the two active switches of the rectifier unit, the LLC resonant converter obtains a wide voltage regulation capability. Of course, the converter also retains soft switching over the entire input voltage and load range. In the meantime, it allows a larger magnetizing inductance under fixed-frequency control, which helps to reduce the circulating current loss. In addition, the voltage stress of switches/diodes for 8-type rectifier unit is low, making it suitable for high-voltage output applications. Finally, a 1000W prototype with 210-420V input voltage and 400V output voltage is made to verify the feasibility and correctness of the theoretical analysis.