Abstract: A utility grid is provided, the utility grid comprising a centralized control means, an intermittent renewable energy source for generating electrical power: at least one further power generation system; and at least one local controller for controlling the total power output of said intermittent renewable energy source and said as least one further power generation system, wherein the centralized control means is connected with the at least one local controller and adapted to request a desired total power output from the local controller.

Abstract: The invention relates to Method of operating a wind turbine, wherein rotor windings of an induction generator, which comprises stator coils coupled to a voltage grid, fed with rotor currents by a feed-in unit are driven by a rotor of the wind turbine; wherein the frequencies of the fed-in rotor currents are controlled depending on the rotor rotation frequency and the feed-in unit is electrically decoupled from the rotor windings in the case predetermined variations of the grid voltage amplitude and the rotor current feed-in is resumed after the decoupling caused by the variation of the grid voltage amplitude, when the currents generated in the rotor windings by the variation have declined to a predetermined value.

Abstract: The invention relates to Method of operating a wind turbine, wherein rotor windings of an induction generator, which comprises stator coils coupled to a voltage grid, fed with rotor currents by a feed-in unit are driven by a rotor of the wind turbine; wherein the frequencies of the fed-in rotor currents are controlled depending on the rotor rotation frequency and the feed-in unit is electrically decoupled from the rotor windings in the case predetermined variations of the grid voltage amplitude and the rotor current feed-in is resumed after the decoupling caused by the variation of the grid voltage amplitude, when the currents generated in the rotor windings by the variation have declined to a predetermined value.