Asymmetric Cascaded Transformer Multilevel AC-DC Converter

This paper presents a multilevel ac-dc single-phase converter with cascaded transformers and two dc links. The configuration is composed by 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 bidirectional operation is not required. The cascaded transformers have different turns ratio characterizing as 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. The proposed configuration is compared with a conventional configuration. Simulation and experimental results are shown to demonstrate the feasibility of the system.