FREQUENCY SUPPORT FROM A POWER PLANT WITH AN ELECTRICAL STORAGE UNIT

The invention relates to a method for controlling a power plant for providing frequency support to a power grid. The power plant comprises an electrical storage unit and a power generating system comprising one or more power generating units including at least one wind turbine generator. The method comprises setting a frequency control period, wherein the electrical storage unit is scheduled to charge or discharge according to a first power set-point and at the start of the frequency control period, charging or discharging the electrical storage unit according to the power set-point. In case of a frequency deviation, a power change of the power from the electrical storage unit is determined based on the frequency deviation. Frequency support is provided by controlling the electrical storage unit to charge or discharge according to a second power set-point determined from the power change.