High-efficiency MOSFET-based MMC for LVDC distribution systems

Low-voltage DC (LVDC) systems offer a promising means for improving distribution system efficiency and reliability. The DC-AC conversion stage, however, is one of the main challenges for LVDC networks. A low-voltage modular multilevel converter (MMC) for LVDC distribution systems is proposed in this paper. Analysis is presented to show that its efficiency can exceed that of a conventional 2-level converter. The low voltage rating of each MMC submodule enables MOSFETs to be used in place of IGBTs to reduce power losses. The application of synchronous rectification (SR) further reduces conduction losses. It is shown that device switching frequency reduces as the number of MMC levels is increased. MMC power losses, for different numbers of levels, are compared with those of a conventional 2-level converter. Simulation and experimental results are presented to confirm the mathematical analysis.