Stability analysis for grid-connected three-phase inverter with LCL filters

A grid-connected inverter is indispensable, for example, for photovoltaic power generation and smart grid systems, and it must be designed and operated stably. This paper proposes a new simple stability analysis method based on a z-domain impedance method for three-phase inverter with a digital control. Then it also proposes a new stability analysis method which considers parameter tolerances. It is a sort of the tolerance analysis based on the Monte Carlo method. The frequency characteristics are computed numerically by a discrete transfer function with Matlab. The computed impedances and stability analysis results are verified both by simulation and by experiment.