Low-Frequency Oscillation Analysis of the Train-Grid System Based on an Improved Forbidden-Region Criterion

With the increasing number of electric locomotives and electric multiple units (EMU) operating in one power section simultaneously, low-frequency oscillation (LFO) may occur. LFO may cause serious railway accidents, which will dramatically influence the stable operation of the power system. In this paper, LFO is solved by establishing a simplified mathematical model of the generalized EMU and a dq-decoupled small-signal model of the single-phase pulsewidth modulation rectifier. Then, an improved forbidden-region criterion (IFRC) is proposed to analyze the stability of the train-grid system and a comparison of the classical criteria is listed to show the advantages of the IFRC. The proposed criterion has less conservatism and higher accuracy than the forbidden-region-based criterion, which has better performance than the classical criteria. Moreover, the analysis result is successfully reproduced by establishing the time-domain simulation model in MATLAB/Simulink and RT-LAB, which verifies the effectiveness and accuracy of the proposed criterion. Finally, the development of IFRC shows the influence of gird parameters, traction parameters, and control parameters of the train-grid system. Ten ways to suppress the LFO are provided according to the simulation results.