Controlling a wind turbine to stabilize an electric grid

A variable speed wind turbine for connection to an electrical grid, configured to provide additional electrical power to counteract non-periodic disturbances in the electrical grid, comprising:

• a rotor with blades coupled to an electrical generator;
• a controller which monitors events indicating a need to increase electrical output power from the wind turbine to the electrical grid to support the stability of the electrical grid, the controller being configured to control the wind turbine to perform grid- stability supporting activity, in a non-periodic manner,
• wherein, after an indicating event has been detected, the wind turbine enters an overproduction period in which the electrical output power is increased beyond a first electrical operating power, wherein the additional electrical output power is taken from kinetic energy stored in the rotor and, if the wind turbine is operating in a partial load-mode, the additional electrical output power is taken without changing the operation of the wind turbine to a more efficient working point,
• wherein, before a rotational speed of the rotor reaches a minimum value the wind turbine enters a recovery period to re-accelerate the rotor to a previous rotational speed while further contributing to the stability of the electrical grid by outputting at least a predetermined minimum electrical power to the electrical grid.