A step-down nesting-type ac–ac converter combined with voltage equalizers and switched-capacitor simple converters

Abstract

In this paper, we present an inductor-less direct ac–ac converter with improved nesting-type topology. Unlike existing direct ac–ac converters, the proposed ac–ac converter combines a voltage equalizer and a switched-capacitor (SC) simple converter. Owing to the nesting conversion using two techniques, the proposed converter can provide a stepped-down voltage with small number of circuit components and high input power factor. To evaluate the performance of the proposed ac–ac converter, we compared the proposed ac–ac converter with existing inductor-less ac–ac converters, namely, flying capacitor type converter, symmetrical type converter, and traditional nesting-type converter, by theoretical analysis and simulation program with integrated circuit emphasis (SPICE) simulations. The SPICE simulations demonstrate that the proposed ac–ac converter outperforms existing inductor-less ac–ac converters in the point of circuit size and input power factor, although the power efficiency of the proposed ac–ac converter is inferior to that of the symmetrical type converter. In the case of 1/4× voltage gain, the proposed ac–ac converter achieves about 82% power efficiency and 0.58 input power factor when the output power is 200 W. Keywords: Inductor-less ac–ac converter, Nesting-type inverter, Switched-capacitor circuits, Step-down converter, Voltage equalizers