Replacement of Arm Inductors by Leakage Inductance of Input Transformers in QAB-CLLC-Based MMC

Abstract

This paper proposes the uniqueness of LFT (line frequency transformer) structure in a QAB-CLLC-based MMC. The LVDC and MVAC sides of the SST (solid state transformer) are both powered through the LFT. In addition, the LFT has a leakage reactance of its own, thereby eliminating arm inductors used in the traditional MMC. The suggested topology can save manufacturing costs while increasing the system power density. Moreover, simulation results are shown to support the validity of the proposed topology. The conversion of 2 MW and 100 kW from MVDC to MVAC and LVDC, respectively, demonstrates the advantages of the novel topology over the conventional MMC.