Magnetically Controlled Scott Transformer (MCST) with Capability of Three Phase Balancing for Electrified Railway Power Supply

The electrified highspeed railway power supplies are normally single-phase, which generates large amount of negative sequence current (NSC) into the three-phase power system. In this paper, a magnetically controlled Scott transformer (MCST) with capability of three phase balancing is proposed. In MCST, the excitation of the Scott transformer is designed as a magnetically controlled variable inductance. As a result, MCST, with the help of fixed capacitor bank, can provide variable reactive power compensation. Consequently, the NSC is eliminated only using reactive compensation. MCST has the advantages of compact structure, simple control, high reliability, and low cost. The configuration and working principle of MCST are analyzed in the paper. The NSC compensation mechanism and control strategy of MCST are presented. A 27.5kV system is simulated in MATLAB/Simulink to verify the NSC compensation of MCST.