Analysis and Design of a High-Efficiency Three-Coil WPT System With Constant Current Output

The wireless power transfer (WPT) system has been widely researched due to its inherent advantages compared with the traditional plug-in charging system over security, flexibility, convenience and so on. Compared with the two-coil WPT system, the three-coil WPT system has been proven to have higher efficiency over a relatively long transmission distance. In many applications, WPT systems are required to have the load-independent constant current output (CCO) characteristic and zero phase angle (ZPA) operation. This study proposes a three-coil WPT system that can achieve the CCO and ZPA operation through flexible parameter design. First, the detailed mathematical deduction for the CCO and ZPA operation is given. Then, a comprehensive analysis of the three-coil WPT system is conducted in term of parameter design, the sensitivity of the CCO to changes in compensation parameters, implementation of zero voltage switching operation and efficiency analysis. Furthermore, a detailed efficiency comparison with the SS WPT system is performed to reflect the high efficiency of the proposed three-coil system, and the additional performance of the proposed three-coil system is compared with previous related works to verify its advantages further. Finally, the correctness of the theoretical analysis is verified by simulation and experiment.