Study on Maximize Efficiency by Secondary Side Control Using DC-DC Converter in Wireless Power Transfer via Magnetic Resonant Coupling

Wireless power transfer via magnetic couple resonance has been widely studied as an attractive research target. In order to improve the transmitting efficiency, not only increasing performance of antenna is important but also controlling secondary (receiver) side input impedance value. As a method of controlling secondary input impedance, the method of using a DC-DC converter is proposed in previous research. Mutual inductance what related to transmitting distance and load resistance value is needed to know for control the DC-DC converter. Moreover, the transmitting distance and load resistance has changed in actual WPT situation. Therefore, control method for DC-DC convertor what keep best efficiency in actual WPT situation is needed. In this paper, the novel method of controlling a DC-DC converter for maximize efficiency which used for wireless power transfer via magnetic couple resonance is proposed. A mutual inductance can be known the voltage sensor in secondary side by setting power supply voltage constant. Furthermore, efficiency could be maximized regardless of the state of load by controlling a DC-DC converter so that the secondary side voltage constant value. This principle was explained by equation. Thereby, even when transmission distance and a load resistance value change, wireless power transfer system keep best efficiency automatically without communication between primary to secondary side.