Transformer-Based Single-Phase AC-DC-AC Multilevel Converter for Voltage Step-Up Applications

This article proposes a single-phase ac-dc-ac multilevel converter composed of a three-leg module series connected to two H-bridges through transformers, sharing the same dc-link, to voltage step-up applications. The proposed structure is appropriated for applications such as uninterrupted power supply and unified power quality conditioner in which the voltage required by the load is higher than the grid voltage available. System model, converter specifications, a space vector PWM strategy, and a control strategy to regulate the dc-link voltage and to control the grid power factor are discussed. The proposed converter generates the input and output voltages with up to seven and eleven levels, respectively, and operates with low dc-link voltage (equal to 20% of the load voltage amplitude). Compared to conventional configurations that have been proposed in the literature, the proposed converter presented as an advantageous alternative in terms of harmonic distortions and semiconductor losses. Simulations and experimental results are presented to validate the theoretical studies.