the grid-connected inverter usually works under the condition of unbalanced grid voltage
unbalanced grid impedance and unbalanced filter inductance. This paper studies impedance modeling and stability analysis of grid-connected inverters under the unbalanced operation conditions. Firstly
under the conditions of unbalanced voltage at the point of common coupling and unbalanced inverter filter inductance
the relationships between the voltage imbalance component
the filter inductance and the harmonic component are derived. Then the output admittance model of the grid-connected inverter in the positive sequence and negative sequence coordinates are developed. Thus the analytical expression of the admittance matrix is obtained
and the characteristics of the positive-sequence
the negative-sequence and the coupling admittances are analyzed. Based on the generalized Nyquist stability criterion and the unbalanced admittance expression of the inverter
the stability analysing criterion of the inverter in the unbalanced situation is given. Finally
experimental results are given to verify the stability criterion.