Magnetic Integrated Double-Trap Filter Utilizing the Mutual Inductance for Reducing Current Harmonics in High-Speed Railway Traction Inverters

Abstract

Current harmonics are generated at the switching frequency and its multiples when the traction converters are modulated. The multi-trap filters can eliminate the harmonic at these frequencies. Therefore, total inductance and filter size can be reduced. Comparatively to traditional inductor-capacitor-inductor (LCL) filters, more magnetic cores are needed for trap inductors. Furthermore, the traction systems have not been examined in conjunction with multi-trap filters. To reduce the filter size and investigate its application in traction converters, this paper presents an integrated double-trap LCL (DTLCL) filter. A tiny capacitor is connected in parallel with the grid-side inductor to form one LC-trap. In addition, another LC-trap is formed by connecting the equivalent trap inductor, introduced through the magnetic coupling between inverter-side and grid-side inductors, in series with the filter capacitor. The presented filters' features are thoroughly analyzed, and the design method has been developed. Finally, the simulation and hardware-in-the-loop (HIL) experiment results validate the proposed method's viability and efficacy. Compared to the discrete windings, the integrated ones enable a size decrease of 35.4%. Furthermore, the proposed filters can meet IEEE criteria with 0.3% for all the harmonics and total harmonic distortion (THD) of 2.36% of the grid-side current.