Input impedance of inverter equipment and its significance in low-frequency track circuits

The authors look at the disturbance mechanisms which may exist between inverter-controlled asynchronous traction drives and low-frequency track circuits which commonly operate at industrial frequency. They present a model for determining the input impedance of inverter-controlled equipment, such that the magnitude of a potentially disturbing interference current, due to substation-generated harmonics, may be calculated. The developed models are shown to be applicable to voltage-source inverters. Practical measurements using low-power inverter equipment are presented to support the proposed models