Abstract
The work presented in this paper aims to show how modern wind turbines can help to control the frequency in a small grid which suffers from large power imbalances. It is shown for an exemplary situation, which occurred in Flensburg’s distribution grid in 2019: a major blackout, which occurred after almost two hours in islanding operation, affecting almost the entire distribution grid, which supplies approximately 55,000 households and businesses. For the analysis, a wind turbine model and a grid support controller developed at the Wind Energy Technology Institute are combined with real measurements from the day of the blackout to generate a fictional yet realistic case study for such an islanding situation. For this case study, it is assumed that wind turbines with grid support functionalities are connected to the medium voltage distribution grid of the city. It is shown to what extent wind turbines can help to operate the grid by providing grid frequency support in two ways: By supplying synthetic inertia only, where the wind turbines can help to limit the rate of change of frequency in the islanded grid directly after losing the connection to the central European grid. In combination with the primary frequency control capabilities of the wind turbines (WTs), the disconnection of one gen set in the local power station might have been avoided. Furthermore, wind turbines with primary frequency control capabilities could have restored the grid frequency to 50 Hz shortly after the islanding situation even if the aforementioned gen-set was lost. This would have allowed connecting a backup medium voltage line to the central European grid and thereby avoiding the blackout.
Highlights
Modern power systems with high penetration of inverter-based renewables are bound to exhibit little system inertia [1]
As the wind turbines (WTs) only provide synthetic inertia (SI), the frequency support is not sufficient to stop the rise of the grid frequency
The results show that the WTs can bring the grid frequency back to 49.99 Hz within 15 s after the event by increasing the power up to 9500 kW
Summary
Modern power systems with high penetration of inverter-based renewables are bound to exhibit little system inertia [1]. To avoid unfavorable excursions of the grid frequency and high rates of change of frequency (RoCoFs), system operators will require the provision of grid frequency support from renewables. Such grid support is already mandatory in some grids for instance in Ireland [2], Québec [3], or India [4]. In an electrical grid large power imbalances i.e., the difference between generation and consumption, can cause heavy excursions of the grid frequency Such contingencies may be caused by the failure of a large power plant, a large line and by a system split. The ENTSO-E regards a system split as a major threat for the continental
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