2018 Volume 138 Issue 6 Pages 522-529
A bi-directional magnetic-resonant wireless power transfer setup was developed, wherein the secondary circuit was a mirror image of the primary circuit. The setup was a combination of four spiral coils with diameters of 20cm, and inverter units operating at approximately 85kHz of standardization recommended frequencies. Using the setup with two wiring schemes, namely, four-closed circuits and conventional two-closed circuits, maximum efficiencies of 94% and 93%, respectively, were demonstrated successfully with a kW-output at a transfer distance of 10cm. Although the fundamental strength of the leakage magnetic field emitted from the four-closed circuits was almost equal to that from the two-closed circuits, the strengths of the harmonic emissions from the four-closed circuits were from 6 to 9dB less than those from the two-closed circuits because harmonic coil currents of the primary side in the four-closed circuits had directions opposite to each other to cancel out the undesirable harmonic field, whereas, in the two-closed circuits, these coil currents were in the same direction to strengthen up the field twice.