Loop gain with sufficient margin usually indicates a good design in terms of small-signal stability. Power factor correction (PFC) converters are designed with a proper loop gain before being installed in the field. However, its actual loop gain will change after being connected to different source impedance, which reflects the system stability condition. For a single-phase and a three-phase-four-wire system, this paper proposes the voltage loop gain models of a PFC converter based on the virtual d-q frame concept and verifies the models with simulation and experimental measurement results. The proposed models are more accurate compared with conventional quasi-static approximation. And the models make it possible to apply loop gain-based stability monitoring of an ac system and guide system operation because it can instruct the understanding of the system conditions’ impact on the PFC loop gain.
