DIRECT MULTI-TO-SINGLE-PHASE, MODULAR MULTI-LEVEL CONVERTER, ITS USE IN A RAILWAY INTERTIE AND METHOD FOR ITS OPERATION

The disclosure relates to a direct multi-to-single-phase, modular multi-level converter, MMC (10), comprising a first AC interface (40) for connecting it to a multi-phase, first power grid (20), in particular a three-phase power grid, a second AC interface (50) for connecting it to a single-phase, second power grid (30), two groups of P phase-legs (80, 90), each phase-leg comprising N switching cells (60) connected in series between a respective one of P phases (L1, L2, L3) of the first AC interface (40) and a single phase (L) and neutral potential (N) of the second AC interface (50), respectively, wherein P≥2 and N≥3, and at least one controller, which is configured to control the first group of P phase-legs (80) and the second group of P phase-legs (90) to selectively provide a maximum apparent power at the first AC interface (40) and at the second AC interface (50), and, in response to the detection of at least one failed switching cell (60) of a first phase-leg, to switch the MMC (10) into a limited output mode of operation, wherein the MMC (10) provides a reduced maximum apparent power at the first AC interface (40) and/or at the second AC interface (50 by controlling at least the first phase-leg, based on a tuning factor k1ph, to output a reduced phase-leg voltage.The disclosure further relates to a railway intertie and a method for operating a direct multi-to-single-phase MMC (10).