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DC-based impedance tuning method using magnetic saturation for wireless power transfer

The transfer efficiency of a resonant wireless power transfer system highly depends on the load impedance and the reactance of the resonators. In many practical applications, these parameters fluctuate by the variation of operating conditions. Therefore, adaptive impedance tuning methods are necessary in order to continuously achieve high-efficiency power transfer. To provide a countermeasure to this problem, this paper proposes a DC-based resonator reactance tuning method which assembles a variable inductor. Based on this reactance tuning method, a DC-based load impedance tuning method which assembles a variable K-inverter is also proposed. This reactance tuning method and load impedance tuning method both utilize the non-linearity of ferrite cores. Through measurements at 6.78 MHz, it is shown that the reactance of the high-Q coil can be tuned from 80 Ω to 113 Ω and the characteristic impedance component of the K-inverter can be tuned from 39 Ω to 72 Ω using non-optimized, basic configurations of the proposed methods.