The harmonic instability caused by the dynamic interactions of traction network and electric trains is threatening the safe operation of trains. Due to the high-power and low-switch-frequency characteristics of the traction converter of electric trains, besides the delay of the inner current loop, the coupling of the control loops is also the main cause of harmonic instability. This paper presents a systematic analysis on the impedance passivity of electric trains based on frequency-domain passivity for investigating the high-frequency impedance characteristic of the electric train. Meanwhile a passivity-based feedforward is introduced to the traditional control system that makes a passive output impedance of electric trains, which improves the interaction system stability. The frequency-domain analysis, simulation tests validate the effectiveness of the suppression method.

impedance, passivity, stability, latency, traction network-electric train interaction.