Maximum efficiency control scheme and design method for resonant circuit of Bi-directional inductive power transfer system

There is a method for charging a battery of electric vehicles by using bi-directional inductive power transfer (IPT). A system applied with IPT is convenient, safe and maintainable. In previous studies, various control schemes for a bi-directional IPT system have been proposed. However, these control schemes are not practical because the resonant circuit controlled with the control scheme is not optimized in efficiency, or the control scheme is highly complex. In addition, these control schemes have less generality because the appropriate design method of the resonant circuit form the viewpoint in the efficiency is not expressed. Therefore, this paper proposes the design method for the resonant circuit in order to obtain high efficiency, and the maximum efficiency control scheme for the resonant circuit considering the characteristics of an IPT system. The proposed control scheme obtains maximum efficiency easily by controlling the 3 control parameters: the magnitude of the primary-side and secondary-side voltages in the resonant circuit, and the phase between the primary-side and secondary-side voltages of the resonant circuit. In addition, these control scheme and design method are derived from the simple theoretical equations. Eventually, the effectiveness of the proposed design method and control scheme are revealed by the experiments.