A high power‐factor lithium‐ion battery charger with series‐input parallel‐output dual bridgeless single‐stage resonant conversion circuit

Summary This study realizes a high power‐factor lithium battery charger which integrates a bridgeless boost‐type power‐factor‐correction converter and a full bridge LLC resonant circuit to constitute a single‐stage topology. The developed lithium battery charger is featured with high power‐factor, current and voltage stresses reduction on components by introducing a pair of converters using series‐input and parallel‐output mechanism. The developed battery charger has the following advantages: (a) bridgeless structure reducing circuit losses; (b) resonant technique usage furnishing power switches with soft‐switching; (c) constant current (CC) and constant voltage (CV) charging power regulation with frequency modulation scheme simplifying the trigger circuit complexity; (d) series‐input and parallel‐output dual converters topology sharing current, voltage stresses, and reducing the component rating; and (e) paired interleaved PFC (power‐factor‐correction) operation sharing current loading and thus increasing charging battery size. Finally, a prototype 2 kW battery charger with 220 V input voltage is implemented and realized. The experimental measurements reveal that the full load efficiency can reach 88% while the power factor exceeds 0.99. In the modulating charging power range, the maximum conversion efficiency can reach to 92%. The paper provides a novel concept for bridgeless power factor correction circuit for lithium battery charger. The proposed lithium battery charger will be implemented with high‐efficiency, high power‐factor, lower current and voltage stresses on switches by using a pair of converters with series‐input and parallel‐output mechanism. The pre‐stage is formed by two series input bridgeless PFC boost converters with LLC resonant function for sharing the high line voltage stress from 220 V ac input. Also, the LLC resonant converter helps to reduce the switching losses with soft switching technique for gaining higher conversion efficiency.