Design and Analysis of a Three-Coil Topology for WPT Applications

In conventional three-coil topologies, when the mutual inductance between the primary and receiver coils is designed to be nonzero, misalignment causes the system to lose its constant output characteristics and degrades overall performance. Moreover, when the mutual inductance between the primary and receiver coil is close to zero, the coupling coefficient between the transmitter and receiver coil will be limited, and the maximum efficiency of the system will be limited as well. This paper presents a new concept for a three-coil design that overcomes the coupling coefficient limitation, enabling the system to achieve higher efficiency, better ZPA, and reduced voltage and current stress across the relay coils. A comparative analysis with other three-coil designs is also presented in this paper, and the experimental results show that the new system can achieve higher efficiency throughout the entire charging process. Moreover, as the load resistance increases, the performance of the proposed system becomes significantly better than conventional three-coil designs. The proposed system could achieve 93.2% dc-dc efficiency while delivering 730 W to the load.