Exponential Modular Multilevel Converter for Low Voltage Applications

This paper presents the structure and control of a single phase Exponential Modular Multilevel Converter (EMMC), which works as a bidirectional AC/DC converter. In addition to the main H-bridge converter, it uses series connected H-bridges with DC link capacitors. The nominal voltage rating of the capacitors is increased with each module by factor of two. In this manner, the number of output voltage levels exponentially increases with the number of series connected H-bridges. By using low-voltage MOSFETs it is possible to achieve a very high efficiency, especially at partial loading. The high number of voltage levels reduces the output voltage THD, while using a low switching frequency. Thus, the required grid filter size can be substantially reduced. Furthermore, the additional capacitor modules increase the nominal output voltage at the AC side, so that the flow of the active and reactive power can be dynamically adjusted. Therefore, the EMMC could be used, for instance, as a vehicle charger directly connected to the grid.