Study of Power Flow in an IPT System Based on Poynting Vector Analysis

This paper analyzes the power distribution and flow of an inductive power transfer (IPT) system with two coupled coils by using the Poynting vector. The system is modelled with a current source flowing through the primary coil, and a uniformly loaded secondary first, then the Poynting vector at an arbitrary point is analyzed by calculating the magnetic and electric fields between and around of the two coils. Both analytical analysis and numerical analysis have been undertaken to show the power distribution, and it has found that power distributes as a donut shape in three-dimensional (3D) space and concentrates along the edges in the proposed two-coil setup, instead of locating coaxially along the center path. Furthermore, power flow across the mid-plane between the two coils is analyzed analytically by the surface integral of the Poynting vector, which is compared with the input power from the primary and the output power to the secondary coil via coupled circuit theory. It has shown that for a lossless IPT system, the power transferred across the mid-plane is equal to the input and output power, which validates the Poynting vector approach. The proposed Poynting vector method provides an effective way to analyze the power distribution in the medium between two coupled coils, which cannot be achieved by traditional lumped circuit theories.