Stability Analysis of Vehicle-Grid Coupling System under Mixed Operation of Locomotives

A large number of power electronic devices intensify the harmonic coupling effects between the locomotive and the traction network, resulting in low-frequency oscillation (LFO) phenomenon in the traction power supply system. In addition, the different control strategies of locomotives lead to disunity of the reference coordinate system, which further aggravates the difficulty in analyzing the stability of system under locomotive mixed operation. To solve the above problems, this paper first considers the frequency coupling effects and establishes the sequence admittance models of different locomotives based on the multi-harmonic linearization method, realizing the unification of different control strategies and converters’ sequence admittance models in the single-phase stationary coordinate frame. Then, the generalized Nyquist criterion (GNC) is used to study the stability of the vehicle-grid coupling system under locomotive non-mixed condition and mixed condition. Finally, based on MATLAB/Simulink simulation and hardware-in-the-loop (HIL) real-time simulation, the correctness of the stability analysis results is verified.