Abstract: Aiming at the engineering problem that the grid-connected inverter is prone to broadband oscillation in the photovoltaic-dominated weak grid environment，this paper focuses on the generation mechanism and oscillation frequency classification of broadband oscillation are systematically combed.The sequence impedance model of photovoltaic inverter is established, and the stability discrimination is carried out by impedance analysis method and Nyquist criterion. The stability margin of photovoltaic grid-connected inverter is determined by sequence impedance modeling and sweep frequency test of 0.2Hz ~ 3000Hz voltage harmonics injection.Based on the RT-LAB semi-physical simulation platform, it is verified that the impedance characteristic phase angle of the grid-connected inverter is in the range of ? 90 ° to + 90 °, the Nyquist curve does not surround the critical point, and the grid-connected inverter is stable.The mechanism analysis-modeling discrimination-simulation verification system is formed, which provides technical support for the broadband oscillation judgment of photovoltaic power station.