S-Transform Based Time–Frequency Evaluation of Dynamic Stray Current in Zero-Resistance Converter System

In DC urban rail transit, stray current causes unneglectable electrochemical corrosion to metallic structures near running rails. In view of the low-frequency and non-stationary distribution of dynamic stray current due to multiple trains in lines, its signal characteristic is significant for the corrosion degree prediction and mitigation performance evaluation. While zero-resistance converter system (ZRCS) is introduced for stray current mitigation, further evaluation of its mitigation performance is essential to field application. Considering that the Fourier transform processing non-stationary signals cannot estimate its frequency-domain features accurately, this paper introduces S-transform to extract the time–frequency characteristics of dynamic stray current in ZRCS. Moreover, the dynamic stray current mitigation performance of ZRCS is verified through time–frequency analysis results.