A comparison of lumped parameter models and Maxwell’s equations for wireless power transfer

Abstract

The main objective of this paper is to compare the lumped parameter models commonly used in the calculation of Wireless Power Transfer (WPT) and the distributed model derived from Maxwell’s equations. First, the WPT between two coils in the harmonic regime is analyzed. A lumped parameter model for WPT between two coils is introduced, and theoretical calculations for power transfer efficiency (PTE) are obtained. Then, the main advantages and disadvantages of this model with respect to the Maxwell’s equations model are discussed and a procedure for parameter calculation is presented. A comparison of the two models is made through two numerical tests: the first representing the charging of a mobile phone and the second involving a wireless charging process of an electric vehicle (EV). Once the PTE is obtained for many frequency values, the calculations are compared, resulting in relevant errors committed by the lumped parameter model under certain conditions. The accuracy of the lumped model is particularly low when distributed eddy currents occur in the WPT problem because the model does not account for this phenomenon, as Maxwell’s equations do. Therefore, the Maxwell’s equations model should be used in such cases, despite its higher computational cost.