An Unfolder-Based Three-Phase AC–AC Converter

This paper presents a three-phase AC-AC converter based on the unfolder topology, which consists of an unfolder rectifier and a T-type three-phase inverter connecting configuration. Since the converter inherits the features of the unfolder circuit such as ultra-low switching frequency and small DC-link capacitance, it exhibits high efficiency and high power density. Furthermore, it eliminates the additional balanced circuit or isolated DC-DC converters required in the conventional unfolder-based power converters, improving power density. To realize both power factor correction (PFC) and output voltage regulation simultaneously, a special modulation scheme for the T-type three-phase inverter is proposed. The feasibility of the proposed converter is verified by theoretical derivation, simulation study and experimental prototype testing.