Method for operating a wind turbine, and a power plant

A method for operating a wind turbine, wherein the wind turbine includes a rotor with rotor blades and a power conversion system mechanically connected with the rotor, the power conversion system configured to convert input motive power into electrical output power and electrically connected to a network for feeding the electrical output power to the network, the method comprising:

• determining a current frequency (f) of the network;
• when the current frequency (f) is equal to or lower than a threshold frequency (fthresh), operating the power conversion system to increase an electrical output power (P) by an output power increase (PI) in accordance with a monotonic function (PI(f)) of the current frequency (f), the monotonic function (PI(f)) being limited to a maximum output power increase value (PImax);
• determining the maximum value (PImax) as a function of a rated power of the power conversion system or as a function of the initial electrical output power (P0);
• wherein the maximum value (PImax) is in a range from about 5% of the rated power or the initial electrical output power (P0) to about 15% of the rated power or the initial electrical output power (P0);
• and
• wherein the monotonic function (PI(f)) comprises two function values including a response value (PIres) larger than zero.

A power conversion plant, comprising:

• a rotor;
• a power conversion system mechanically connected with the rotor and configured to convert input motive power into electrical output power, the power conversion system connectable to a network;
• a sensor connectable to the network that measures at least one signal correlated with a current frequency (f) of the network;
• a controller communicatively coupled with the power conversion system and the sensor, the sensor configured to:
• receive and use the at least one signal to determine the current frequency (f);
• determine, when the current frequency (f) is equal to or lower than a threshold frequency (fthresh), an electrical output power increase (PI) for the power conversion system in accordance with a monotonic function (PI(f)) of the current frequency (f), the monotone function (PI(f)) being limited to a maximum value (PImax) determined as a function of an initial electrical output power (P0) of the power conversion system;
• and
• use the electrical output power increase (PI) for controlling the power conversion system.