Instability and oscillation issues have frequently occurred in high-speed railways due to the mismatch of impedances versus frequency between the 4-quadrant converter (4QC)-based high-speed train and the traction network (hereinafter train-network). However, solely utilizing the mathematical deduction to quantify the impedances appears to be difficult owing to unknown detailed parameters of both traction network and electric train. This paper proposes a method to measure the equivalent impedances of traction network and the 4QC of electric train in the stationary frame for stability analysis. A disturbance circuit consisted of anti-parallel insulated gate bipolar transistor (IGBT) modules and an excitation load is adopted by means of the pulse width modulation (PWM) signal to drive the IGBTs. Consequently, a desired broad spectral excitation is then generated to measure the output impedance of the traction network. When injecting the harmonics twice which are linearly independent at the same frequency, the input impedance of 4QC of the electric train can be calculated at the corresponding frequency considering the frequency-coupled effect. The proposed method shows a good measurement accuracy. Additionally, the stability and oscillation issues of the train-network system can be then identified using measured impedances. Both simulation and experimental results confirm the effectiveness of the proposed measurement methods.
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