Single-Phase AC-DC-AC Five-Leg Multilevel Converter

This article presents a new single-phase ac-dc-ac five-leg multilevel converter, which is composed of a three-leg converter cascaded with an H-bridge converter by means of a transformer. As a result, its output voltages have five, seven, and nine levels when a transformer turns ratio equal to eta = 1, eta = 2, and eta = 3, respectively, is used. The system model, operation principles, and a control strategy are presented and discussed. Additionally, two space-vector pulsewidth modulation techniques are developed to optimize the proposed converter. The proposed converter was compared with the conventional three-leg converter in terms of power semiconductor losses, harmonic distortion, and dc-link voltage requirement. The reduction in the dc-link voltage is of 50%, 66.7%, and 75%, for eta = 1, eta = 2, and eta = 3, respectively. This characteristic reduces the voltage rating of the power devices, leading to the use of cheaper devices with better characteristics. Furthermore, when compared to other multilevel solutions presented in the literature, the proposed topology has a simple control structure and fewer power devices. As a multilevel topology, the proposed converter present competitive efficiency and can be applied with good performance in applications such as universal power filters and uninterruptible power supplies. To validate the theoretical analysis, simulated and experimental results are presented and discussed.

Automated summary

The article introduces a new five-leg multilevel converter with varied output voltages achieved by using a transformer, which was validated through simulated and experimental results.