Hybrid mode-hopping modulation for LLC resonant converter achieving high efficiency and linear behaviour

Frequency modulation (FM) has been widely used in the inductor-inductor-capacitor (LLC) resonant converter due to excellent soft switching features. However, low power efficiency in light load conditions and complex control due to the nonlinear converter behaviour are common concerns for the FM method. In this study, a hybrid mode-hopping modulation method is proposed for the LLC resonant converter to address these challenges. The LLC resonant converter operates at any two of three power-efficient operating modes for a different amount of time within a single modulation period. By determining the mode hopping time and combining different mode-hopping modulations, the LLC resonant converter can achieve a wide range of output power and maintain high efficiency at the same time. Besides, since the switching frequencies are fixed, the relationships between the duty cycle and the output power are linear, which can significantly simplify the control design. Compared with the existing modulation methods, the proposed hybrid mode-hopping modulation makes the LLC resonant converter behaves linear, simplifies the control design, achieves wide operation range and ensures high efficiency even in light load condition.