T‐type direct AC/AC converter structure

Abstract

In this study, a novel T-type topology for single-phase direct AC/AC conversion is proposed. In this topology, frequency changing takes place directly (without common DC voltage bus) through three converters that are connected in a T structure. Unity input power factor and precise output voltage and frequency regulation is achieved through appropriate control of these three converters. H-bridge converters can be used in each branch of T to make the proposed converter. The converter is controlled such that the average active power of each H-bridge remains zero. Therefore, capacitors are implemented in DC links of H-bridges. Moreover, using half-bridge converters, instead of H-bridge ones, for T branch converters, leads to an AC/AC converter with only six semiconductor switches. Also, multilevel inverters, specially cascaded H-bridge can be used in branches of T. This will lead to a multilevel AC/AC converter that is suitable for high-power applications such as intertie connections and high-power motor drives. Principle of operation and control schemes of the converter are then explained. Simulation and experimental results verify the performance of the converter while operating as a power supply at different frequencies.