Introduction  The potential positive feedback of virtual inertia and damping control (VIDC) may exacerbate the interaction within the control loop, causing low-frequency oscillation of bus voltage and disrupting the stability of electric vehicle DC charging station (EVCS). Although the existing multi-timescale impedance model explains the stability mechanism of VIDC and the low-frequency oscillation mechanism of VIDC-controlled-EVCS, it is essentially a high-order transfer function, making it difficult to obtain analytical expressions for damping control strategies.

  Method  Therefore, a detailed impedance analysis of the virtual impedance of the loop was conducted to intuitively reveal the fundamental reasons for the higher-order properties of each loop impedance.

  Result  A closed-loop gain fitting method for the control loop was proposed through Bode diagram approximation, and a low-order impedance circuit model was established.

  Conclusion  The effectiveness of the proposed multi-timescale impedance model is verified through Matlab/Simulation.