Coupling Impedance Modeling Analysis of Grid-Connected Inverters Under Three-Phase Voltage Unbalance

Under the condition of asymmetric system voltage, grid-connected inverters exhibit obvious sequence impedance frequency coupling characteristics, which can easily lead to resonance and the misoperation of protection and control devices. Currently, targeted quantitative analyses are insufficient. To address this limitation, this paper identifies dominant harmonic pairs and develops an analytical model of an inverter’ second-order admittance under unbalanced grid voltage conditions. Considering the influence of the phase-locked loop and current control loop, the sequence impedance characteristics of a grid-connected inverter were quantitatively analyzed. The simulation results verified the accuracy of the model. The conclusion of the paper provides a foundation for subsequent research on the instability mechanism and oscillation suppression strategy of the grid-connected inverter and grid interconnection system.