A Multilevel Converter Based on Cascaded Flying Cells with High Modularity and Single DC-link per Phase

Abstract

In cascaded H-bridge (CHB) converter, despite its high modularity, each h-bridge cell requires an isolated dc-source. The phase-shifting transformer in cascaded h-bridge (CHB) converter is its main drawback. New topologies have been introduced with a reduced number of DC sources e.g. MMC. But it needs lots of semiconductor components. A new topology is proposed in this paper which is called cascaded flying cells (CFC). This topology provides high modularity and uses a single DC-link per phase. A sorting algorithm is proposed in this paper by which the voltages of flying capacitors in the converter cells are kept balanced with a constant switching frequency. Compared to several reduced count multilevel converters, it provides high modularity and better controllability of capacitor voltages. The proper operation of a five-level CFC is simulated in both steady-state and dynamic conditions in MATLAB/SIMULINK environment.