Traction transformer integrated LCL filtering method for high-frequency harmonic and resonance suppression in AC train

Abstract

Converters in AC-DC-AC traction drive system introduce a wide range of high-frequency harmonics. When the high-frequency harmonics contain contents at around the inherent resonance frequency of the traction power supply system, it will cause harmonic resonance in the traction grid. The LCL-type single phase line-side converter is widely adopted to prevent the high-frequency harmonics from entering the traction grid. However, additional four inductors and four capacitors are needed to form the filtering system, which increases the occupied onboard space. In this paper, a traction transformer integrated LCL filtering method is proposed to achieve high-frequency harmonic and resonance suppression and, at the same time, reduce the space occupied by the LCL filter. The equivalent circuit of the traction transformer integrated LCL filtering system is modeled and the mechanism of harmonic and resonance suppression is analyzed. Then, the required equivalent impedances of the traction transformer, the filtering capacitor, and the corresponding controller of line-side converter are designed. Finally, the parameter design of the traction transformer prototype is verified by finite element simulation. And the grid-train system with the traditional L filter, LCL filter, and the proposed traction transformer integrated LCL filter are simulated by real-time field-circuit coupling simulation, which verifies the good filtering effect of the proposed method.