Capacitive Charge-Secondary Side Phase Shift Control Method for LLC Resonant Converter

Variable frequency control is often utilized in LLC resonant converters; however, this method has a limited voltage gain range, exhibits bipolar points in the transfer function, and shows poor dynamic performance. To address these issues, this paper introduces a capacitor charging-secondary side phase shift control method. This approach involves using a voltage sensor to monitor the resonant capacitor voltage, allowing control of input charge to adjust system gain. In this configuration, the LLC resonant converter operates like a typical first-order system, maintaining a certain level of stability. When the resonant capacitor voltage reaches a predefined maximum, the system automatically transitions to secondary-side phase shift control, where the gain is adjusted by modifying the phase shift angle of the secondary-side power switch. This method effectively expands the voltage gain range for capacitive charge control.