This paper proposes a novel admittance model for a grid-connected voltage-source converter (VSC) system in polar frame. In the admittance model, the power factor of VSC can be explicitly expressed and the influence of power factor on stability can be analyzed intuitively. Based on this admittance model, the grid-connected VSC system can be modelled as a single-input single-output (SISO) system. Moreover, from a small-signal stability perspective, we prove that when controllers’ parameters are fixed, a change of the VSC’s power factor can be equivalent to a change of the grid’s impedance. The validity of the model and analysis is verified by simulation results.

power factor,small-signal stability,admittance model,voltage-source converter (VSC),single-input single-output (SISO)