Wind turbine generator and method of controlling the same

1. A wind turbine generator, comprising:

at least one wind turbine blade;

a power generator connected to the wind turbine blade and configured to generate power from a rotational force of the wind turbine blade, the power generator being connected to a utility grid to output the power to the utility grid; and

a control unit configured to perform an interconnected operation with the utility grid, the control unit including:

a detecting unit for detecting an operation state parameter related to an operation state of the power generator;

a demand value obtaining unit that stores therein first information containing (i) a relation between the operation state parameter and active power demand value and (ii) a maximum value of an active power set to a rated value, the demand value obtaining unit configured to receive the operation state parameter from the detecting unit and to obtain an active power demand value corresponding to the operation state parameter detected by the detecting unit from the first information; and

a changing unit configured to

receive a request for changing the maximum value of the active power and a newly defined maximum value of the active power from the utility grid, and

change the maximum value of the active power in the first information to the newly defined maximum value of the active power at a change rate determined based on the maximum value of the active power in the first information and the newly defined maximum value of the active power received from the utility grid.

2. The wind turbine generator according to claim 1 , wherein the changing unit stores therein an upper limit of the change rate and a time required for changing the maximum value of the active power in the first information to the newly defined maximum value of the active power received from the utility grid, and is configured to calculate the change rate by dividing a difference between the maximum value of the active power in the first information and the newly defined maximum value of the active power received from the utility grid by the time, to employ the calculated change rate as the change rate in a case where the calculated change rate is equal to or less than the upper limit, and to employ the upper limit of the change rate as the change rate in a case where the calculated change rate exceeds the upper limit.

3. The wind turbine generator according to claim 1 , wherein

the changing unit stores therein a plurality of pieces of second information each containing the relation between the operation state parameter and active power demand value and a different maximum value of the active power between the maximum value of the active power set to the rated value and the newly defined maximum value of active power, and upon receiving the request for changing the maximum value of the active power and the newly defined maximum value of the active power from the utility grid, is configured to change the maximum value of the active power in the first information to the newly defined maximum value of the active power step by step by using the plurality of pieces of second information.

4. A wind farm comprising a plurality of wind turbine generators, wherein at least one of the plurality of wind turbine generators is the wind turbine generator according to claim 1 .

5. The wind turbine generator according to claim 1 , wherein the operation state parameter is at least one of rotation speed of a rotor of the power generator or an excitation current of the rotor.

6. A method of controlling a wind turbine generator including a wind turbine blade, a power generator connected to the wind turbine blade and configured to generate power from a rotational force of the wind turbine blade, the power generator being connected to a utility grid to output the power to the utility grid, and a control unit for controlling the wind turbine blade and the power generator, the method being performed by the control unit, the method comprising:

detecting an operation state parameter related to an operation state of the power generator;

storing first information containing a relation between the operation state parameter and active power demand value and a maximum value of the active power set to a rated value;

obtaining an active power demand value corresponding to the operation state parameter detected in the detecting from the first information;

receiving a request for changing the maximum value of the active power and a newly defined maximum value of the active power from the utility grid; and

changing the maximum value of the active power in the first information to the newly defined maximum value of the active power at a change rate determined based on the maximum value of the active power in the first information and the newly defined maximum value of the active power received from the utility grid.

7. A method of controlling a wind farm having a plurality of wind turbine generators, wherein the method of controlling a wind turbine generator according to claim 6 is applied to at least one of the plurality of wind turbine generators.

8. The method according to claim 6 , further comprising:

storing an upper limit of the change rate and a time required for changing the maximum value of the active power in the first information to the newly defined maximum value of the active power received from the utility grid, wherein

the changing includes

calculating the change rate by dividing a difference between the maximum value of the active power in the first information and the newly defined maximum value of the active power received from the utility grid the time,

employing a calculated change rate as the change rate in a case where the calculated change rate is equal to or less than the upper limit, and

employing the upper limit of the change rate as the change rate in a case where the calculated change rate exceeds the upper limit.

9. The method according to claim 6 , further comprising:

storing a plurality of pieces of second information each containing the relation between operation state parameter and active power demand value and a different maximum value of the active power between the maximum value of the active power set to the rated value and the newly defined maximum value of active power, wherein

the changing includes changing the maximum value of the active power in the first information to the newly defined maximum value of the active power step by step by using the plurality of pieces of second information.

10. The method according to claim 6 , wherein the operation state parameter is at least one of rotation speed of a rotor of the power generator or an excitation current of the rotor.