A Hybrid Active Compensation Method for Current Balance Based on Y,d11 Connection Traction Transformer

Electrified railway traction loads present large single phase loads to the supply system. Most of traction transformer use Y,d11 connection in china. Typically zero sequence components are removed using a phase to phase transformer connection, however a large negative sequence component remains. With the developing of high speed and heavy load of the train, low power factor, high contents of harmonic currents, and negative-sequence current in traction power systems become more critical. This paper presents a novel hybrid compensation method to compensate reactive power, harmonic, and negative-sequence currents in two feeders of a traction substation. The system structure of current balance compensator method is constituted by an AC-DC-AC single-phase inverter, base frequency and high-frequency harmonic passive filter to suppress harmonic current, negative-sequence current and reactive current. It detects the active current difference of two phase traction loads, and then makes active power flows from the light load side to the heavy side through the compensator. The result is two phase traction loads of the transformer reach to balance state to insure the current symmetry of three-phase side of the Y,d11 connection traction transformer.