Frequency stability for distributed generation connected through grid-tie inverter

Conventional power generation systems rely on the rotating inertia of large synchronous generators to maintain stability in the power balance and frequency control loops. The increasing penetration of inverter-connected distributed generation proportionally reduces the fraction of conventional stabilized power used in the distribution system. It is an open question whether the primary feedback loop related to frequency control would remain stable as the fraction of the distributed generation increases in a distribution system. We develop and analyze a control model of a grid-connected distribution system to determine the stability in response to disturbances from the grid, such as grid frequency variations. Our conclusion is that for tie-in inverter connection of distributed generation, the transients can remain stable and grid frequency disturbances will not be amplified as long as the inverter controller is well-tuned. This conclusion holds for a broad range of parameter values explored in this work percentage of the distributed generation penetration, power factor of the load, load power, transmission line impedance, LCL filter and PLL in inverter system.