Reduced Switch Count Step-Up/Step-Down Switched-Capacitor Three-Phase AC-AC Converter

A direct three-phase ac-ac converter based on the switched-capacitor principle and ladder structure is presented in this paper. Additionally, the boundary between partial charge and no charge modes of a switched-capacitor operation is defined. All switched-capacitor direct ac-ac converters described in the literature employ four-quadrant switches; however, the proposed structure works with two-quadrant switches. This characteristic is the main advantage of the proposed structure because it reduces the number of MOSFETs employed in the power circuit, increasing the converter reliability. Furthermore, the proposed converter can operate as a step-up or step-down circuit, i.e., it is a bidirectional topology. The converter offers high performance with regard to efficiency, power density, and power factor, and it can also be used as an electronic autotransformer. The analysis, design methodology, and experimental results obtained with a prototype with 220/110 V and 3.5 kW are described herein. At the rated power, an efficiency of 95.1% for step-up and step-down modes, capacitive power factor of 0.94, and output voltage regulation of 96% were obtained.