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Frequency Splitting Phenomena of Magnetic Resonant Coupling Wireless Power Transfer

In magnetic resonant coupling wireless power transfer (WPT) system, the frequency splitting phenomena have a vital influence on the output power. This paper mainly focuses on the frequency splitting of two-coil and three-coil WPT. First, the frequency characteristics of transfer power and system efficiency of the two-coil WPT are analyzed by circuit theory. In addition, the magnetic field distribution of the two splitting frequencies is simulated to analyze which frequency is better for the operating frequency. Second, considering the reference resistance of RF power, the frequency splitting of two-coil and three-coil WPT is analyzed. Finally, the critical coupling, which determines the over coupled region, of two-coil and three-coil WPT is derived. Meanwhile, we propose a tuned frequency method according to the numerical results. In addition, the transfer power can be kept at a relatively constant level in the over coupled region.