On Facilitating the Modular Multilevel Converter Power Scalability Through Branch Paralleling

Abstract

Modular multilevel converter current scalability challenge can be significantly alleviated by connecting its branches in parallel. In case a predefined submodule design is to be used with the aim of serving a certain span of applications, methods of achieving desired current scalability of the modular multilevel converter rely upon numerous hardware adaptations. Contrary to that, for the same goal to be achieved, paralleling of the branches eliminates the need for a major redesign of the existing converter parts. Consequently, superior operational flexibility can be achieved with most of the effort being concentrated in the control domain, allowing for less costly solutions to be realized. This paper provides a thorough control analysis of the modular multilevel converter operating with an arbitrary number of parallel connected branches.

Virtual Capacitor Concept for Computationally Efficient and Flexible Real-Time MMC Model

“…10b. Thereafter, dynamics of the MMC AC currents can be described with (7) to (9), where L Σ = L g + L br /2, which is identical to the expression that can be derived from the parent circuit provided in Fig. 4.…”

“…1, a series connection of an SM cluster and an inductor L br is referred to as the branch, whereas two branches form the leg. By stacking SMs in series, theoretically unlimited voltage scalability is provided, while current capacity increase can be achieved in several ways [9], [10]. In spite of the advantages mentioned above, series connection of SMs comprises a high number of switching devices, making the MMC implementation challenging for any real-time simulator.…”

A Review of Multilevel Converters With Parallel Connectivity

“…Hybrid MMCs are IEEE POWER ELECTRONICS REGULAR PAPER potential candidates for connecting two ac grids (e.g., a singlephase grid and a three-phase grid). In principle, we can parallel multiple MMCs, CHBs, or hybridize other macro-level topologies as long as their terminals match [142], [143].…”

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

“…Interestingly, the existing literature does not consider another powerextension option, which alleviates many of the mentioned problems while providing certain advantages. Namely, the MMC current capacity increase can also be achieved through the paralleling of the branches [8], as presented in Figure 3(d). Since the branch represents the topological feature specific to the MMC, the identical approach can be employed in all MMC-alike circuits (e.g., matrix MMC, Δ-STATCOM, and so on).…”