Implementation and Stability of Charge Control for Full-Bridge LLC Converter

The LLC resonant converter offers improved efficiency and high power density in many applications. However, its conventional single-loop frequency control cannot provide high dynamic performance. The two-loop charge control can significantly improve the LLC converter response to line and load disturbances. Previous research was focused on the charge control for the half-bridge LLC converter. However, for several practical reasons, the charge control implementation in the half-bridge and full-bridge LLC converters is different. Key issues for the full-bridge converter control are sensing the signal related to the charge delivered by the resonant inductor current and stability. To analyze stability of the proposed charge control, large-signal and small-signal discrete-time models were developed and applied to a 400 V/12V, 1 kW LLC converter.