A Control Method Based on Power Factor for Improving Output Voltage Stability and Efficiency of LLC Converter in Wide Range of Output Voltage and Load Impedance

The LLC converter is attractive for its small volume and comparatively high efficiency. However, the application of this converter is limited to the power supply to a static load with almost constant output voltage and current because the LLC design covering a wide range in the output voltage and the load variation can deteriorate the output voltage stability and efficiency. This paper addresses this issue by proposing a novel control method. Unlike the conventional control, which adjusts the operating frequency to stabilize the output voltage, the proposed control adjusts the power factor of the transformer primary-side to achieve the same excellent dynamic performance as the buck chopper. Simulation supported the effectiveness of the proposed control at a wide load variation range.