Highly-Efficient Battery Chargers with Parallel-Loaded Resonant Converters

The well established advantages of resonant converters for battery chargers, including fast response, low switching losses, easy of the control scheme, simplicity of circuit configuration, and low electromagnetic interference (EMI), among others, have led to their increasing attraction. This work develops a highly efficient battery charger with a parallel-loaded resonant converter for battery charging applications to improve the performance of traditional switching-mode charger circuits. The charging voltage can be regulated by varying the switching frequency. The switching frequency of the parallel-loaded resonant battery charger was set at continuous conduction mode (CCM). Circuit operation modes are determined from the conduction profiles. Operating equations and operating theory are also developed. This study utilizes the fundamental wave approximation with a battery equivalent circuit to simplify the charger circuit analyses and presents an efficient, small-sized, and cost-effective switched-mode converter for battery chargers. A prototype charger with parallel-loaded resonant converter designed for a 12V-48Ah battery is built and tested to verify the analytical predictions. The maximum charging efficiency of the proposed battery charger topology is as high as 90.9%. Satisfactory performance is obtained from the experimental results.