An Impedance Measurement Method at Controlled Frequency Band for Both Traction Power System and Electric Train

Abstract

Abstract Electric railway systems occur instability and oscillation frequently for the mismatched impedances between the traction power system (TPS) and the voltage-source-converter (VSC)-based electric train. However, the parameters of both TPS and electric train (hereinafter TPS-train) are not fully known so that utilizing the mathematical deduction to quantify the impedances is difficult. This paper gives a method to measure the impedances at controlled frequency band. A chirp-PWM signal is introduced and utilized to drive the insulated gate bipolar transistor (IGBT) modules of disturbance circuit, which can produce a desired broad spectral excitation at controlled frequency band. The impedances can be then calculated with the corresponding response voltages and currents after connecting the disturbance to the tested system. Then, the stability and oscillations can be identified using the measured TPS and electric train impedances. The proposed method is easy to implement with its simple hardware structure and software control, and also it gives a high measurement accuracy. Simulations verify the effectiveness of this method.