Power Cycle Modulation Control of LLC Resonant Converters for Wide Voltage Gain Range Applications

Abstract

This paper proposes Power Cycle Modulation (PCM) control method of LLC converters for wide voltage gain range applications. Instead of switching frequency modulation, the proposed PCM method operates the LLC converter according to a control period comprising an on cycle operation mode for a duration $T_{on}$ and an off cycle operation mode for a duration $\boldsymbol{T}_{off}$. $\boldsymbol{T}_{on}, \boldsymbol{T}_{off}$ and the optimal switching frequency during $T_{on}$ are adjusted based on the sensed input and output voltages. Optimal switching pulse pattern can be maintained under the low output voltage and high input voltage conditions, which ensures the high efficiency. A 65W prototype is built to verify the feasibility and validity of the proposed control method.