Automatic selection scheme of most efficient operation mode in buck-boost type secondary-side converter for inductive power transfer

There is a case where an inductive power transfer (IPT) system is applied to battery charger for electric vehicles. A secondary-side converter, which consists of a DC-DC converter with a diode bridge rectifier, is connected to the secondary-side of the resonant circuit in order to regulate the current and voltage of a battery. Previously, the authors showed that the IPT system connected to a buck-boost type secondary-side converter is more efficient than the system connected to a buck type secondary-side converter. However, the applied buck-boost type secondary-side converter has some operation modes, which are buck mode, boost mode and buck-boost mode; and the selection scheme of the operation modes in the converter had not been considered yet. Therefore, this paper proposes an automatic mode selection scheme of the most efficient operation mode in the buck-boost type secondary-side converter for an inductive power transfer according to the input voltage and the output power variations of the converter. In addition, the effectiveness is verified by experiments and theoretical analysis. As a result, it was confirmed that the total and converter efficiencies of the IPT system with the buck-boost type secondary-side converter in the buck and boost modes were better than those of the system with the buck-boost type secondary-side converter in the buck-boost mode.