Frequency-Splitting Analysis of Four-Coil Resonant Wireless Power Transfer

Based on four-coil magnetically coupled resonant wireless power transfer, this paper demonstrates, explains, and analyzes the frequency-splitting phenomenon by using the circuit theory. First, the complete and simplified models are built to describe the whole system. The numerical formulas of the system efficiency both at and away from the resonant frequency are presented. Then the frequency-splitting phenomenon is displayed and further explained mathematically and physically. An important factor for frequency splitting is introduced. The boundary condition for frequency splitting and its splitting frequency points are deduced. The amplitude-frequency and phase-frequency characteristics of the input impedance are measured and described to verify the explanation. Three related factors are studied, and the sensitivity analysis is conducted. A solution is proposed that helps improve the efficiency when frequency splitting occurs. The theoretical calculations and experimental results provide a sound basis.