Single-Phase AC-DC-AC Multilevel Five-leg Converter Based on a High-Frequency Transformer

This paper investigates a single-phase ac-dc-ac multilevel five-leg converter based on a high-frequency transformer. The system consists of a three-leg module with a full-bridge module connected to the shared part of the system. In the proposed configuration, the dc link of the three-leg module is supplied by the full-bridge module through a single active bridge converter. This feature improves the power quality and efficiency of the structure and simplifies the design of the control strategy compared to the conventional solution that uses floating capacitors. The proposed system is composed of a shunt unit and a series unit. The first one is responsible for compensating reactive power and harmonic currents, while the second one provides load voltage compensation against voltage sags and harmonics in the grid voltage. In addition, the proposed converter operates with low dc-link voltages in applications with the same input and output frequency, such as unified power quality conditioner. The model of the system, a space-vector pulse-width modulation and the overall control scheme are addressed. Simulations and experimental results are presented to confirm the feasibility of the proposed converter and the correctness of the design methodology.