## Impedance-based analysis of grid harmonic interactions between aggregated flyback micro-inverters and the grid

Grid harmonic interactions due to aggregated flyback micro-inverters are investigated in this study. An impedance-based model based on the Norton model of flyback micro-inverters, which are with quasi-resonant peak-current control, is obtained by adopting the small-signal modelling approach. As a supplement to the existing output impedance modelling of string inverters with linear controllers, further study on micro-inverters under non-linear control is addressed in this study. Based on the derived impedance model, the admittance matrix of aggregated micro-inverters connected to the grid is formulated and the impedance-based analysis of the system stability is also presented. Consequently, by modelling the output admittance of the quasi-resonant peak-current controlled flyback micro-inverters, harmonic interactions with a distorted grid can be effectively forecasted. Results obtained from modelling, analysis and verifications have shown that the proposed method is a simple and valid way of dealing with the harmonic quasi-resonance problems.