Efficiency Analysis of the Secondary-side Buck-boost Type Converter for Inductive Power Transfer System

Abstract

An inductive power transfer (IPT) system is sometimes applied to the battery charger of electric vehicles. A DC-DC converter with a diode bridge rectifier (secondary-side converter) is connected to the secondary side of the resonant circuit in order to regulate the current and voltage of a battery. In an IPT system, the secondary-side voltage of the resonant circuit changes significantly depending on the coupling coefficient between the primary coil and the secondary coil. In addition, the voltage changes depending on the load condition. Therefore, a buck-boost converter is suitable for the secondary-side converter because the output voltage range is wider than the other converters, and the IPT system with the buck-boost converter is more efficient than the IPT system with the buck converter. In order to develop a high-efficiency IPT system, a theoretical analysis that considers the characteristics of the IPT system is required. Thus, in this paper, the relationship between the coupling coefficient of the coils and the loss of the secondary-side converter is investigated in order to develop a high-efficiency IPT system with theoretical analysis and experiments that consider the coupling coefficient of the coils. In addition, the circuit parameter selection guideline that makes the secondary-side converter more efficient is shown on the basis of the results of theoretical analysis and experiments. As a result, it was confirmed that the tendency of the characteristics obtained with the experiments is similar as that of theoretical analysis. Thus, it was indicated that theoretical analysis in this paper is useful in analysis of the efficiency and loss of the whole IPT system including secondary-side converter.