Sequence impedance modeling and stability mechanism analysis of three-phase grid-connected inverter considering frequency coupling

At present, the impedance analysis method has been widely used in the stability mechanism analysis of the interactive system between grid connected inverter and power grid. Considering the influence of frequency coupling, the positive and negative sequence impedance is no longer decoupled, and the generalized nyquist criterion needs to be used for analysis, which makes the system analysis complex. Based on this, this paper first modifies the impedance matrix to realize the equivalent transformation from multiple input multiple output (MIMO) impedance matrix model to single input single output (SISO) impedance model. Secondly, for the equivalent SISO system, the nyquist stability criterion is used in the frequency domain to analyze the influence of the system short-circuit ratio, PLL bandwidth, current loop bandwidth and other parameters on the system stability. Theoretical analysis and simulation results show that the system short-circuit ratio increases, the PLL bandwidth decreases, the current loop bandwidth increases, and the system stability improves. Finally, the correctness of impedance model and theoretical analysis is verified by time domain simulation.