Power output changes by ramping de-rated power output and de-rated rotor speed

1. A method of controlling a de-rated power output of a wind turbine generator, the wind turbine generator associated with a predetermined power ramp rate upper limit and operating with a de-rated rotor speed, the method comprising:

ramping, upon receiving a target power level, the power output from an initial power level to the target power level during a ramping interval, wherein during a first portion of the ramping interval, the power output is ramped at a first power ramp rate less than the power ramp rate upper limit;

ramping the rotor speed to a predetermined rotor speed value contemporaneously with ramping the power output during the first portion of the ramping interval; and

calculating a result of a predetermined power output limiting function having a current value of the power output as an input, the power output limiting function selected to support the contemporaneous ramping of rotor speed during the first portion of the ramping interval, wherein the first power ramp rate is determined based on the power output limiting function.

2. The method of claim 1 , wherein the first power ramp rate determined based on the power output limiting function avoids causing the wind turbine generator to enter reduced loading operation.

3. The method of claim 1 , further comprising:

determining, based on current wind conditions, a minimum rotor speed value to meet the target power level, wherein the predetermined rotor speed value is the determined minimum rotor speed value;

ramping the rotor speed to the minimum rotor speed value during the first portion of the ramping interval; and

upon reaching the minimum rotor speed value, ramping the power output to the target power level at a second power ramp rate greater than the first power ramp rate.

4. The method of claim 3 , wherein the first power ramp rate is substantially zero, and wherein the second power ramp rate is the power ramp rate upper limit.

5. The method of claim 1 , further comprising:

ramping, during a second portion of the ramping interval prior to the first portion, the power output from the initial power level to a predetermined first intermediate power level at a second power ramp rate greater than the first power ramp rate.

6. The method of claim 5 , wherein the power output is ramped from the first intermediate to a predetermined second intermediate power level during the first portion of the ramping interval, the method further comprising:

ramping, during a third portion of the ramping interval subsequent to the first portion, the power output from the second intermediate power level to the target power level.

7. The method of claim 6 , wherein the first intermediate power level corresponds to a maximum power output value for the wind turbine generator at a current rotor speed, and wherein the second intermediate power level corresponds to a predetermined optimal rotor speed based on current wind conditions.

8. The method of claim 1 , wherein the power output limiting function comprises a sum of the current value of the power output and a term including a predetermined acceleration parameter.

9. The method of claim 8 , wherein the term comprises the predetermined acceleration parameter multiplied by an interpolation term based on a value of available power and a maximum power output value for a current rotor speed.

10. A control arrangement for controlling a de-rated power output of a wind turbine generator (WTG), the WTG associated with a predetermined power ramp rate upper limit and operating with a de-rated rotor speed, the control arrangement comprising:

a processor coupled with a pitch control module and a calculation module, and configured to:

ramp, using the pitch control module and in response to receiving a target power level, the power output from an initial power level to the target power level during a ramping interval, wherein during a first portion of the ramping interval, the power output is ramped at a first power ramp rate less than the power ramp rate upper limit; and

ramp the rotor speed to a predetermined rotor speed value contemporaneously with ramping the power output during the first portion of the ramping interval,

wherein the calculation module is configured to calculate a result of a predetermined power output limiting function having a current value of the power output as an input, the power output limiting function selected to support the contemporaneous ramping of rotor speed during the first portion of the ramping interval; and determine the first power ramp rate based on the power output limiting function.

11. The control arrangement of claim 10 , wherein the calculation module is configured to determine the first power ramp rate based on the power output limiting function to avoid causing the WTG to enter reduced loading operation.

12. The control arrangement of claim 10 , further comprising a measurement module configured to acquire current wind condition data for the WTG,

wherein the processor is further configured to:

determine, based on the current wind condition data, a minimum rotor speed value to meet the target power level, wherein the predetermined rotor speed value is the determined minimum rotor speed value;

ramp the rotor speed to the minimum rotor speed value during the first portion of the ramping interval; and

upon reaching the minimum rotor speed value, ramping the power output to the target power level at a second power ramp rate greater than the first power ramp rate.

13. The control arrangement of claim 10 , wherein the processor is further configured to:

ramp, during a second portion of the ramping interval prior to the first portion, the power output from the initial power level to a predetermined first intermediate power level at a second power ramp rate greater than the first power ramp rate.

14. The control arrangement of claim 13 , wherein the processor is further configured to:

ramp the power output from the first intermediate to a predetermined second intermediate power level during the first portion of the ramping interval; and

ramp, during a third portion of the ramping interval subsequent to the first portion, the power output from the second intermediate power level to the target power level.