Comparative Study on the Operating Area of M3C and B2B MMC for Soft Open Point Application

Back-to-back modular multilevel converter (B2B MMC) and modular multilevel matrix converter (M3C) are generally considered as two promising topologies used for soft open point (SOP) in medium-voltage distribution network (DN). SOP is utilized to control the power flowing through its grid-tied point and thus its working performance is closely related to the operating area of its topology. In this paper, considering the conditions of DN and limitations of topologies themselves, the steady-state operating areas of B2B MMC and M3C are calculated and analyzed in detail, which provides theoretical basis for topology selection. After establishing the equivalent circuit model, operating constraints are explored. Finally, the power regulation capacities of the two topologies in different cases are presented intuitively by P-Q graphs. The results demonstrate that B2B MMC has an advantage over M3C in operating area and it is more economical than M3C for transformerless SOP. The causes are also explained.