Design and Optimization of Constant Frequency Wide Range Output PWM-LLC Converter

In the current field of converters, converters with wide-range output have become an important research and development direction. The traditional LLC converters controlled by Pulse Frequency Modulation (PFM) face various complex working conditions and it is difficult to simultaneously meet the two important indicators of wide-range output and high efficiency. Pulse Width Modulation (PWM) control is widely applied in converters with wide output ranges, so it is feasible to consider introducing PWM control into LLC converters. In this paper, a PWM-LLC converter with wide-range output and constant frequency is proposed. In terms of the converter topology, this converter only replaces one diode of the secondary-side full-bridge rectifier with a MOSFET, without adding any redundant components, yet the output range is greatly expanded. Regarding losses, under certain conditions, this topology can achieve Zero Voltage Switching (ZVS) for all MOSFETs and Zero Current Switching (ZCS) for diodes to reduce losses. Finally, a converter with a switching frequency of 355KHz, a rated input of 100V, a rated output ranging from 300V to 600V, and a peak power of 1200W is designed. This converter achieves a peak efficiency of 96.5% and has a wide output range.