Operational Advantages and Challenges of New AC-AC Converter Solution with Modular Multilevel Structure Suitable for High-Power Medium-Voltage Electrical Machine Drives

Lately, many high-power electrical applications are emerging to keep up with the fast growth of the modern industry. Proper power-electronic converters are required to drive these systems. The modular multilevel converter is the state-of-the-art solution for high-voltage applications that require a DC stage and that operate with a fixed frequency at their AC terminals. This converter topology can reach high voltage levels while operating with high power quality, high reliability and low switching frequency. The modular multilevel converter, however, presents some drawbacks such as its intolerably high submodule-capacitor voltage ripple at low frequencies and its high component count. Thus, many different converter topologies have been proposed in the literature as alternatives for high-power medium-voltage AC-AC applications, especially applications that operate at very low frequencies such as machine drives. These converter topologies present their own drawbacks and, thus, finding new converter solutions for high-power machine drives is still a topic with high research interest. In this paper, the operational characteristics and challenges of a new converter topology are presented and discussed. The proposed converter presents advantageous characteristics in comparison to other alternative topologies, indicating that it could be a suitable option to drive high-power medium-voltage electrical machines.