An Efficiency Optimization Method Based on Double Side Impedance Angle Design for Wireless Power Transfer System

Wireless power transfer (WPT) system has already been applied to battery charging occasions, and the charging process can be roughly divided into two stages: constant current mode (CCM) and constant voltage mode (CVM). In CVM, researchers always focus on the effect of the primary phase angle (PPA) on the system efficiency but rarely pay attention to secondary phase angle (SPA). A large SPA will also lead to a decrease of system efficiency, which should be worth more attention and consideration when designing the system parameter. The double-sided LCC compensation topology can not only achieve constant current or constant voltage output at different frequencies but also has the advantage of high parameter design freedom, so it is very suitable for battery charging scenarios. Considering the influence of the PPA and SPA on the system efficiency, a novel parameter design method based on double-sided LCC compensation topology is proposed in this article. By changing the system operating frequency, the switching between CCM and quasi-constant voltage mode (QCVM) is realized. In order to verify the feasibility and practical effect of the parameter design method, an experimental prototype based on a planar square coil was established and three groups of comparative experiments were conducted. The experimental results show that the optimized WPT system efficiency is significantly improved under the same power level. The maximum output power of the system is 620 W. When the optimized system works in CCM and QCVM, the maximum efficiency is about 95%.