A Series-Connected Hybrid Modular Multilevel Converter for HVDC Tapping Application

This paper introduces a three-phase series-connected asymmetric hybrid modular multilevel converter (SCAH-MMC) tap which not only retains the technical advantages of the three-phase series-connected MMC, but also has the capability to cope with dc faults. Basic operation principle of SCAH-MMC is presented. It shows that SCAH-MMC is troubled by the inherent third harmonic of single-phase ac power. By adding feed-forward to the modulation signal, third-harmonic currents of SCAH-MMC can be significantly reduced. The mathematical formulas and claims are validated by simulations using PSCAD/EMTDC.