Analysis and Design of Wireless Charging Systems Without Extra Components for Load-Independent Constant Current and Voltage Battery Charging

Wireless charging technologies have meaningful advantages over the conventional plug-in method in the future Electric vehicle development. To improve the battery service life and ensure charging safety, a wireless charger should provide a representative charging process with constant current (CC) and constant voltage (CV) outputs. Usually, different kinds of compensation topology are combined into a hybrid or reconfigurable circuit to meet the charging requirements. However, these topologies may introduce extra components, resulting in higher power loss and control complexity. This paper proposes a frequency control-based wireless power transfer (WPT) system using only a single compensation network, which achieves load-independent CC and CV outputs. Furthermore, the impacts of internal coil resistors and variations of the coil self inductors on system performance (such as zero voltage switching (ZVS) and output charging current) are investigated. A simple parameter tuning method for robust ZVS is put forward to obtain a higher charging performance. Besides, a frequency control strategy is proposed for accurate CC charging and improving the system's robustness against gap and misalignment variations. Finally, experimental results nearly show no difference with the theoretical analysis and verify the proposed frequency control-based WPT system.