Suppression of Low-Frequency Oscillation with Cascaded H-bridge Multi-level Active Power Filter in Vehicle-Grid System

In recent years, The low-frequency instability phenomenon frequently occurs in the vehicle-grid system of high-speed railway when multiple units (EMUs) operate in one railway station simultaneously, which leads to the traction blockade of EMUs and directly influences the normal operation of high-speed railway system. To solve this problem, a single-phase cascaded H-bridge multi-level active power filter (APF) directly connected to the 27.5kV traction network is proposed, which can operate in two different modes. In mode 1, APF is only utilized for inter-harmonic compensation, while in mode 2, APF is utilized for inter-harmonic and reactive compensation. To verify the suppression effect of APF on the low-frequency oscillation (LFO), some time-domain simulations in MATLAB are implemented. The simulation results show that the APF can suppress the LFO effectively in both modes. Moreover, it is also verified that the change of system parameters have little impact on the performance of APF.

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