Impedance stability analysis method and parameter design of photovoltaic grid-tied inverter with repetitive control

Stability is one of the critical topics in photovoltaic grid-tied inverters using repetitive control (RC) to achieve excellent capability of suppressing harmonic distortion. With the fluctuation of grid impedance affecting the stability of inverters, analysis and solution methods are essential for RC. In this paper, the impedance stability of RC controlled inverter is discussed with the criteria of small gain theorem. Specifically, the grid impedance is separated from other system blocks in the criteria, in which the grid impedance is transferred into stable boundary. Then, further analysis is carried out to figure out the design margin of kernel parameters. A detailed parameter design procedure is given, and experiments are carried out under different grid impedances to verify the validity of the analytical method and parameter design.