Analysis and Suppression of Oscillation in Traction Network-EMUs Coupling System Under the Condition of Rising Pantograph

Low frequency oscillation (LFO) incidents may occur in coupled system composed of electric multiple units (EMUs) and traction network, which threaten the safety and stability of EMUs and traction power supply system. In order to solve this problem, a virtual impedance with band-pass filter link control strategy is proposed for the four quadrant converters (4QCs) of EMU. First, the impedance models of coupled system under the background of LFO are established based on the impedance matching. Next, this paper defines the worst scenario for coupled system, combined with the Nyquist curve and forbidden region criterion (FRC). The impact of the grid-side and EMU-side circuit parameters on system stability is analyzed. The proposed control strategy adjusts the input impedance of the EMUs equivalently by virtual impedance to meet FRC. Band-pass filter (BPF) is used to select a specific band to apply virtual impedance. This avoids passive impact on the dynamic performance of other frequency band. The parameters of the virtual impedance and BPF are designed according to the FRC and engineering requirements. The simulation results verify the effectiveness of the proposed control strategy for oscillation suppression. Finally, the coupled system model is built on the basis of hardware-in-the-loop experimental platform. The experimental results show that the proposed method can be used to suppress oscillations.