Comparison between the 2N+1 and N+1 operating modes of the single-phase AC-AC MMC

This paper compares the 2N+1 and N+1 operating modes of the single-phase AC-AC MMC. Unlike conventional DC-AC applications, the AC-AC MMC offers versatile operating combinations based on the number of levels in the common-mode voltage and the differential-mode output voltage. By applying multilevel modulation strategies such as Phase-Shifted Pulse-Width Modulation and Staircase, these voltages improve power quality at the converter’s input and reduce the output voltage. The 2N+1 operating mode results in a lower voltage level across the input inductor of the AC-AC MMC converter when using the same number of cells in each arm, compared to the N+1 operating mode. Simulation results demonstrate the ACAC MMC operating under medium-voltage and medium-power conditions, emphasizing the key differences between the two operating modes.