Using Input Impedance to Calculate the Efficiency Numerically of Series-Parallel Magnetic Resonant Wireless Power Transfer Systems

Analysis of magnetic resonant wireless power transfer systems aims to achieve maximum efficiency of the power transfer. From the analysis we wish to derive the maximum power and the frequency at which this occurs. This paper presents a method to estimate these two required values and to achieve this requires the solution of the input impedance equation numerically. The frequency of the maximum efficiency is found when the imaginary of the input impedance is close to zero, and it could be different to the natural resonant frequency. We estimate the efficiency value which depends on the real value part of the input impedance. The proposed method has been applied to one of the four types of possible connections; a series-parallel (SP) connection although similar approaches could be applied to the others. In some cases the maximum efficiency shifts away from the resonant frequency. Therefore, this paper shows how to use the same equations to achieve maximum efficiency at resonance and suggests a design method to achieve this practically