A Family of Hybrid Topologies for Efficient Constant-Current and Constant-Voltage Output of Magnetically Coupled Wireless Power Transfer Systems

In the field of wireless charging technology for electric vehicles, the charging process of lithium-ion batteries is typically divided into two stages: constant-current (CC) charging and constant-voltage (CV) charging. This two-stage charging method helps protect the battery and extend its service life. This paper proposes a family of circuit topology design schemes that achieve a smooth transition from CC to CV charging stages by using two relays. Additionally, the paper derives the corresponding system efficiency formulas and provides constraints on device parameters to ensure that the charging efficiency remains high during different charging stages. The proposed family of circuit topologies adopt unified device parameters and relay control logic, simplifying the design and operation process, and making these topologies more suitable for large-scale applications. To verify the practical performance of these topologies, the paper constructs experimental prototypes and conducts tests. The experimental results show that the proposed family of topologies can stably achieve CC and CV output, with smooth transitions between the two charging modes, and the efficiency can be maintained above 89% before and after mode switching over a wide load range. Furthermore, the mode switching points of the proposed family of topologies are multiples of two.