Design consideration of CC-CV controller of LLC resonant converter for Li-ion battery charger

In this paper, the design consideration of the dual control scheme of a LLC resonant converter for a Li-ion battery charger is proposed to stabilize operation during whole charging process. The theoretical approach of constant-current and constant-voltage controller is presented when considering the nonlinear property of a Li-ion battery under wide ranged output voltage. By applying the extended describing function method, the small-signal ac model of the resonant converter is obtained. The feedback controller is designed to guarantee stable and robust, while providing a desired crossover frequency and sufficient phase margin. Several simulation results are provided in order to verify the effectiveness of the proposed design consideration.