fa Railway track and structures Railway track and structures پژوهشي Research <strong>Abstract </strong><br> Traditional railway power supply systems impose substantial power quality problems (PQ) on the utility network, such as unbalance, harmonics and a large amount of reactive power. This paper proposes a topology based on three-phase to single-phase modular multilevel converters (MMC) to obviate these problems. The MMC based traction substations (TSS) are connected directly to the utility grid through the three-phase side of MMC. The proposed system symmetrically transfers active power from three-phase grid to the single-phase overhead catenary system (OCS) which compensate negative sequence current (NSC), reactive power and harmonics simultaneously. Eliminating of bulky traction transformers (TT), integrating of OCS, removing the neutral sections and increasing the train speed are the advantages of presenting system. The Precise simulations have been provided simulation have been provided to verify the performance of the proposed method. Electric railway system, Traction substation, Modular multilevel converter, Power quality 39 47 http://ijrare.iust.ac.ir/browse.php?a_code=A-10-88-19&slc_lang=fa&sid=1 Hamed Jafari Kaleybar 180031947532846001438 180031947532846001438 No 2Department of Electrical Engineering, Sahand University of Technology, Tabriz, Iran 2Department of Electrical Engineering, Sahand University of Technology, Tabriz, Iran Hossein Madadi Kojabadi 180031947532846001439 180031947532846001439 Yes 2Department of Electrical Engineering, Sahand University of Technology, Tabriz, Iran 2Department of Electrical Engineering, Sahand University of Technology, Tabriz, Iran Seyed Saeed Fazel 180031947532846001440 180031947532846001440 No 2Department of Electrical Engineering, Sahand University of Technology, Tabriz, Iran 2Department of Electrical Engineering, Sahand University of Technology, Tabriz, Iran Federica Foiadelli 180031947532846001441 180031947532846001441 No Department of Energy, Politecnico di Milano, Milan, Italy Department of Energy, Politecnico di Milano, Milan, Italy Morris Brenna 180031947532846001442 180031947532846001442 No Department of Energy, Politecnico di Milano, Milan, Italy Department of Energy, Politecnico di Milano, Milan, Italy