Comparison of Double Star Topologies of Modular Multilevel Converters in STATCOM Application

Abstract

The modular multilevel converters (MMCs) have shown great emphasis in academic studies of the last decades, specially applied in renewable energy systems, HVDC systems, energy storage, electrical drives and STATCOMs. In STATCOM applications, in particular, the Double Star (DS) configuration has several operating advantages, mainly related to its ability to compensate negative sequence components and unbalanced currents. Considering the advantage of these topologies in STATCOM application, it is proposed in this work a comparison of two DS topologies: Double Star Chopper-Cell (DSCC) and Double Star Bridge-Cell (DSBC). These topologies are compared in terms of steady-state operation, power losses and costs. In addition, two variations of DSBC topology are approached: DSBC-2L, which employs 2-level modulation and DSBC-3L, which employs 3-level modulation. The three MMC topologies are designed based on a 15 MVA STATCOM connected in a 13.8 kV grid. The simulation results validate the design methodology and also indicates the DSBC-3L topology as a promising solution for medium voltage STATCOMs due to its costs, protection during short circuits and smaller insulation requirements.