Improved inertia and frequency support from grid-connected DFIG wind farms

Several techniques have been suggested to enhance the ability of multi-megawatt DFIG wind turbines to contribute in arresting system frequency decay and provide primary control power upon power imbalances. Among such techniques, the capability of temporary active power over-production was shown to be useful in limiting the initial frequency dip in hydro dominated systems. However, the excess active power production is followed by an acceleration period whose negative effect on system frequency profile is analyzed herein. This paper suggests an improved technique generalized for slow-response power systems. This technique not only avoids the acceleration period, but also reduces the frequency excursion and injects primary frequency control power until secondary control takes up the power imbalance. Moreover, a means of obtaining a power reserve from DFIG WFs at low wind speed is analyzed and quantified. The dynamic model of a sample slow-response power system is built in which all the presented techniques are tested for different wind penetration levels. The results of calculations indicate the reduced frequency nadir and improved support obtained from DFIG-WFs for all wind speeds, in a manner compliant with the current requirements of system operators.