An Improved Controlled-Frequency-Band Impedance Measurement Scheme for Railway Traction Power System

Railway traction power system (TPS) impedance affects the stability and operation performance of connected power electronics devices (i.e., electric trains) with the closed-loop control system. In order to identify the detailed TPS impedance, the wideband-response-based impedance measurement technique has become attractive for its fast execution time and accuracy, especially the chirp-based technique for its bilateral controllability of injected wideband disturbance. However, for the reason that the disturbance device is directly powered by the measured system, the fundamental component separates some harmonic clusters in the frequency domain and leads to unsatisfactory uniformity of the injected wideband disturbance. In this article, a segmented-chirp-based technique is proposed to eliminate this phenomenon caused by the fundamental component, where the chirp signal is segmented and carried on the fundamental only when the amplitude is relatively smooth on top (or bottom), which facilitates a uniform wideband distribution to keep a good measurement accuracy. Meanwhile, the presented modular disturbance circuit with a flexible topology can better adapt to the various industrial engineering conditions. Finally, the detailed measurement results based on the simulation and downscaled experimental system validate the effectiveness of the proposed measurement scheme.