Measurement of Impedance-Frequency Property of Traction Network Using Cascaded H-Bridge Converters: Device Design and On-Site Test

To investigate the harmonic resonance in electric railways, determination of the traction network impedance using a utility instrument is an important and challenging task. This article presents a novel industrial test device which can directly measure the impedance of the actual traction network which is the power source of the railway. The structure arrangement and the parameter design are accomplished to meet the requirements for high-voltage level and strong anti-electromagnetic interference capability. Following this, frequency-dependent impedance measurement is implemented through the injection of controlled harmonic currents using the cascaded H-bridge converters. Furthermore, the power flow analysis is carried out to demonstrate that this device does not need any additional power source and can generate harmonic power. In a new-built railway, this device has been adopted to conduct the on-site test of the traction network impedance. Then, the multi-conductor simulation model is established for the purpose of mutual verification between the field test result and simulation result. Furthermore, the on-site test results can be applied to determine the resonance frequency before a nenw-built line is put into use so that any harmonic resonance can be avoided by taking effective measures in advance.