Protection Scheme of Flexible Traction Power Supply System based on MMC structure

With the rapid development of railway system, the construction of a more energy-saving and safe traction power supply system is urgently demanded. In this paper, a flexible traction power supply system (FTPSS) structure is proposed, which can realize the whole line connection. However, due to the high-power power electronic equipment contained in its system, the fault characteristics are different, the fault complexity is increased, and the failure rate might be increased. The fault characteristics of FTPSS have changed greatly, and the existing protection scheme is no longer applicable. Therefore, this paper makes a detailed introduction to the modular multilevel converter (MMC), including its working principle and the establishment of a mathematical model. According to the previous analysis and summary, the possible fault locations and corresponding fault conditions in the system are summarized. A protection scheme based on current limiting control is proposed to ensure safe and reliable operation of FTPSS. Finally, simulations results verify the correctness and rationality of the proposed protection scheme.