Stability analysis of a grid-connected inverter system

A stability analysis method for parallel connected inverters to a grid system is investigated to analyze their stability behaviors. Basically frequency characteristics of the system impedance divided by the inverter output impedance are checked to satisfy the Middlebrook criterion. First a numerical computation method for the impedance is proposed. Then grid-connected inverter examples are analyzed for their stability. Basic behaviors and characteristics are analyzed and investigated for a single and a parallel connected inverter systems numerically and experimentally.