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

In this paper, a single-phase AC-DC-AC multilevel five-leg converter based on a high-frequency transformer (HFT) is investigated. The system consists of a three-leg module with an H-bridge connected to the shared part of the system. The power quality and efficiency of this type of converter are improved when it operates with asymmetrical dc-link voltages. However, the problem related to the control complexity to balance the dc-link voltage when floating capacitors are used is presented. In this way, the proposed configuration uses a high-frequency link (HFL) that simplifies the design of the control strategy. The proposed converter operates with low dc-link voltages in applications with the same input and output frequency, such as uninterruptible power supplies (UPS) and unified power quality conditioners (UPQC). System model, a space-vector PWM, and an overall control scheme are addressed. Simulations and experimental results are presented to confirm the feasibility of the proposed converter as well as the correctness of the design methodology.