Asymmetric Cascaded Transformer Multilevel AC-DC Converter

This article presents a multilevel single-phase rectifier with cascaded transformers and two dc links. The configuration is composed of k cascaded transformers, which isolate the load from the power source, and 2(k+1) two-level (2L) legs, in which some insulated-gate bipolar transistor (IGBT) legs can be replaced by diode legs if the bidirectional operation is not required. The configurations have different turns and dc-link voltage ratios, characterizing an asymmetric configuration. In addition, the second dc link is used to increase the number of voltage levels, which results in better input voltage quality. This dc link has a lower voltage and can be a floating capacitor. Furthermore, the nearest-level control (NLC) technique is used to generate voltage with high power quality. The proposed configurations are compared with conventional configurations. Finally, experimental results are shown to demonstrate the feasibility of the system.