A method for feeding electrical power, by a one wind power installation, a power plant or a generation plant, into an electrical supply grid is provided. The grid has a grid voltage having a grid frequency at a grid connection point. In the method a reference system having a reference frequency, a reference phasor having a reference angle, and a reference amplitude of an output voltage are specified. The reference angle revolves at the reference frequency and the reference frequency substantially corresponds to the grid frequency. A phase angle between the output voltage and the grid voltage is specified and an infeed angle is determined. The output voltage is generated having a voltage amplitude depending on the reference amplitude, a frequency depending on the reference frequency and the infeed angle. Tracking of the behavior of the grid voltage is delayed by the reference system.