Influence of Soil Medium on Resonant Wireless Power Transfer System

For underground magnetic coupled resonant wireless power transfer system, the soil as the transmission medium will produce eddy current in the alternating magnetic field and reduce the transmission efficiency. The corrected transmission efficiency formula containing the conductivity and permeability is proposed which bases on Maxwell equations, circuit theory and Hashin-Shtrikamn theory. And the field-circuit coupled model of the migrable wireless power transfer system in soil is developed. The influence rule of medium parameters on the optimal resonant frequency and energy transmission efficiency is obtained by finite element simulation. A transmission efficiency optimization scheme is proposed and an experimental platform is built to carry out experimental research. The simulations and experiments shows that when the equivalent conductivity reaches 0.45S/m, the optimal resonant frequency of the system decreases by 3MHz and the energy transmission efficiency decreases by 7.50%. When the equivalent permeability reaches 1.42, the optimal resonant frequency of the system decreases by 3MHz, and the energy transmission efficiency decreases by 50.72%. It provides theoretical and data support for practical engineering application.