Impedance-Based Sensitivity-Criterion for Grid-Connected Three-Phase Inverters

Utilization of renewable energy sources such as solar and wind power requires affordable, reliable and efficient methods for grid connection. Most often, grid-parallel inverters are applied. As the number of inverter-connected resources in the power grid increases, they start to have a significant effect on the dynamics of the power system. The inverters have been shown to produce harmonic oscillations. To avoid producing or amplifying the harmonic content in the power grid currents and voltages, sensitivity of the inverter against external distortion should be analyzed. This paper provides a method for sensitivity analysis of the inverter. The sensitivity is analyzed by applying a forbidden region in the complex plane, which is based on the maximum-peak criterion that is often applied in the field of control engineering. The system is defined to have robust stability if the minor-loop gain formed by the inverter output impedance and the grid impedance stays out from the forbidden region.