On Power Scalability of Modular Multilevel Converters: Increasing Current Ratings Through Branch Paralleling

The modular multilevel converter (MMC) presented in Figure 1 found its place within high-voltage and medium-voltage (MV) applications owing to the possibility of effortlessly meeting the imposed voltage requirements by stacking the so-called submodules (SMs) in a series [1]. Therefore, high-quality voltage waveforms can be synthesized across the MMC ac terminals, while using the power devices of a lower voltage rating, resulting in a very modest or even no filtering requirement on the grid side. Depending on the application, the SMs are mainly half bridge (HB) or full bridge (FB), not including the other types of SMs reported in the literature [2]. According to Figure 1, a cluster of SMs in a series connection with an inductor Lbr will be referred to as the branch, whereas two branches comprise the leg.