Completed Compensation Strategy Research of Railway Power Conditioner for Negative-sequence Current Under Unbalanced AC Power Grids

Railway power conditioner (RPC) with traditional compensation strategy can completely compensate the negative sequence current in V/v traction transformer railway system under balanced power grid voltage. However, it is difficult to fully compensate the negative sequence current when there is negative sequence component in power grid voltage. Firstly, this paper studied the completed compensation mechanism that the current flowing through the secondary side of V/v traction transformer should be equal in magnitude and phase difference 120 degrees. Secondly, the mechanism of how negative sequence voltage affects the secondary voltage of V/v traction transformer and RPC compensation performance was analyzed. Thirdly, to completely compensate the negative sequence current, the method of separating the positive and negative sequence voltages based on the secondary side voltage of V/v traction transformer was proposed. In addition, the analytical expressions of reference currents for converters were also derived and presented. Finally, simulation models were built to verify the correctness and effectiveness of the proposed method from the aspects of compensation strategy performance comparison, dynamic and transient response characteristics. © 2020 Chin. Soc. for Elec. Eng.