Feature-based solution to harmonics interference on track circuit in electrified heavy haul railway

Traction current will increase severely and cause remarkable conductive interference or unbalanced current on signal of track circuit under the condition of electrified heavy haul railway, this may lead to malfunction of signaling system. Features of both signal and harmonics of interference are basis for identifying them since harmonics may occupy the position in signal pass band. In this paper, at first, quantitative results of unbalanced traction current harmonics were presented and evaluated considering power frequency drift. Then, after illustrating typical frequency domain distribution of both harmonic interference and track circuit signal featuring Frequency Shift Keying modulation, the Zoom Fast Fourier Transform algorithm was introduced and applied to obtain higher frequency resolution for the purpose of signal identification. Finally, a systemized solution based on their features was proposed to mitigate even eliminate the harmonic components in signal pass band, and to accurately recognize signal. Simulation and application demonstrated that this solution was feasible and effective.