Among the various topologies proposed in literature, the Modular Multilevel Converter (MMC) is considered the next generation of converters for medium and high voltage applications. This paper presents a comparison between two variants of modular multilevel converters for STATCOM applications: The Double-Star Chopper Cell (DSCC-MMC) and the Single-Delta Bridge Cell (SDBC-MMC). These converter topologies are compared and benchmarked during positive and negative sequence compensation. The comparisons are supported by analytical results regarding minimum effective dc-link voltage, number of cells, current rating, energy storage requirements and operation during unbalanced conditions. The dynamic behavior, power losses and cost of both solutions are evaluated through simulation model of a 15 MVA MMC STATCOM.

The modular multilevel converters (MMCs) have become an attractive topology in recent years. The MMC has been employed in several applications as HVdc, energy storage, renewable energy, electrical drives, and static synchronous compensators (STATCOMs). One advantage of MMC-based topologies is the inherited fault-tolerant operation associated with the high number of submodules (SMs). This work proposes the study of four redundancy strategies, which can be employed in modular multilevel converters: standard redundancy, redundancy strategy based on additional submodules (RAS), redundancy strategy based on additional submodules optimized (RASO), and redundancy strategy based on spare submodules. These strategies are compared through a case study of a 15 MVA MMC STATCOM. A new approach for the SM capacitance design is proposed, including the effect of the negative sequence current in the converter storage energy variations. The comparisons of the redundancy strategies are accomplished based on dynamic behavior, capacitor voltage balancing, control complexity, and power losses. Finally, the advantages and drawbacks of each redundancy strategy are presented.

Recent works have highlighted the growth of battery energy storage system (BESS) in the electrical system. In the scenario of high penetration level of renewable energy in the distributed generation, BESS plays a key role in the effort to combine a sustainable power supply with a reliable dispatched load. Several power converter topologies can be employed to connect BESS to the grid. There is no defined and standardized solution, especially for medium voltage applications. This work aims to carry out a literature review on the main converter topologies used in BESS and highlight the main advantages and disadvantages of each one. The topologies used for each conversion stage are presented and their combinations are analyzed. In addition, the different services that BESS can carry out when connected to the distribution system are analyzed in order to demonstrate all the main contributions to the electrical systems. Finally, a case study is performed to compare and analyze the converter topologies for BESS, considering some aspects such as efficiency, power quality and number of components.