Method and wind energy system for feeding electric power into an electricity supply grid

A wind energy system, comprising:

• one or more wind power installations configured to feed electric power into an electricity supply grid via a connection node, wherein:
• the wind energy system or each wind power installation of the one or more wind power installations is converter-controlled, and
• the electricity supply grid has a grid voltage and a grid frequency and is associated with a nominal grid voltage and a nominal grid frequency;
• and
• a central controller configured to:
• determine the grid voltage of the electricity supply grid;
• determine a delayed differential angle based on the grid voltage, wherein the delayed differential angle corresponds to a difference between a determined phase signal that indicates a temporal profile of a phase angle of the grid voltage and a phase signal that is delayed with respect to the determined phase signal;
• determine a grid impedance for the connection node;
• and
• set an infeed power for the wind energy system based on the delayed differential angle and the grid impedance.