Low-frequency Stability Analysis and Enhancement of Vehicle-grid System Considering the Impact of SOGI

Low-frequency oscillation (LFO) has been frequently triggered in the electric multiple units (EMUs) and traction power grid interaction system (hereinafter called vehicle-grid system). As an essential component of the rectifier of EMUs, the second order generalized integrator (SOGI) also contributes to the LFO. Still, its impact has yet to be fully studied in previous research. This paper reveals the respective influence of voltage and current SOGI on the low-frequency stability of vehicle-grid systems based on the equivalent single-input and single-output (SISO) impedance models of the rectifier of EMUs and grid. It is found that the bandwidth of both two SOGIs can affect the negative resistance character of the EMUs rectifier, thus affecting the stability of system. Besides, compared to the voltage SOGI bandwidth, the system stability is more sensitive to the current SOGI bandwidth. In this regard, to effectively suppress the LFO in the vehicle-grid system, a trap filter-based current SOGI (TF-SOGI) is proposed to adjust the bandwidth of the current SOGI equivalently. The design of the TF-SOGI parameters is clarified by considering the dynamic response speed and the system stability simultaneously. Then, the superiority of the proposed TF-SOGI in LFO suppression to the existing SOGI is verified via the Bode plots of the equivalent SISO impedance model. Finally, the simulations on the controller hardware in the loop (HIL) platform are implemented, further validating the theoretical analysis's accuracy and the superior performance of TF-SOGI in LFO suppression.