Winding loss analysis of planar spiral coil and its structure optimization technique in wireless power transfer system

Circular planar spiral coils are wildly used for the magnetic coupling system in a high-frequency wireless power transfer system. The loss of the magnetic coupling system usually takes dominance in the whole system. This paper built the calculation model of magnetic field strength and coil loss, the proposed calculation model can effectively consider the mutual influence between the transmitter and receiver coil and accurately calculated the AC loss of WPT coils. Then, the effect of turn spacing on the AC resistance of coil is analyzed. It reveals that the proximity effect loss is greater when the coil is tightly wound, and the AC loss can be optimized by designing the turn spacing. Based on the above analysis, a double-layer coil method is proposed. This method can reduce the AC loss and improve the quality factor (Q) without changing the mutual inductance and footprint of coil at high frequency. The AC resistance of the double-layer coil method can be greatly reduced compared with the general method through simulation and experiment. The work efficiency of WPT system is increased by 4.3%, which verifies the accuracy and flexibility of theoretical analysis.