An Efficient Topology of Modular-Multilevel Converter with Alternative Arm Operation

In this paper, a new configuration of modular-multilevel converter (MMC) is proposed, which is the modified structure of the alternative-arm converter (AAC) with the improvements in terms of cost, loss, footprint, and device count. The proposed MMC also operates through alternatively conducting and blocking the upper and lower arms in a leg as the AAC, where a common stack of full-bridge submodules (FBSM) is shared for the upper and lower arms. This results in a reduction of the SM number in the converter leg, consequently for the whole MMC, from which the number of DC capacitors of the SMs is also reduced resulting in a significant reduction in cost and volume of the converter and improving the reliability of the converter. Extra active switches are required to control the common stack to operate with either the upper or lower arms. Furthermore, the proposed MMC also provides the fault-handling capability and reactive power compensation to the electric grid under the DC-cable short circuits. Simulation results for a 17-level MMC modeled by PSIM have been shown to verify the feasibility of the proposed scheme under normal operation and DC-fault conditions.