Methods and systems for operating a wind turbine
Methods of operating a variable speed wind turbine in an event of a power set-point limitation are described. The methods may comprise determining whether the power set-point is below or equal to a theoretical capability of the wind turbine in accordance with prevailing wind conditions. If the power set-point is below the theoretical capability, operating the wind turbine to generate power according to the power set-point, including operating the wind turbine according to a generator torque and a generator rotor speed predefined for the power set-point. Each power set-point is defined by a combination of a generator rotor speed and a generator torque, the generator rotor speed (ω min , ω 1 , ω 2 , ω max ) being outside an exclusion band.
1. A method of operating a variable speed wind turbine, the wind turbine having a rotor with a plurality of blades, a generator, and a wind turbine controller for controlling a torque of the generator and a pitch angle of the blades,
the wind turbine having an operational rotor speed range extending from a minimum rotor speed to a maximum rotor speed, the operational rotor speed range including one or more exclusion bands of rotor speeds related to excitation of structural modes,
the method comprising:
operating the wind turbine according to a predefined power curve when there is an absence of a power set-point limitation, the predefined power curve defining combinations of the pitch angles of the blades and the generator torque as a function of a wind speed;
in the event of a power set point limitation, determining whether a power set-point is below or equal to a theoretical capability of the wind turbine in accordance with prevailing wind conditions;
when the power set-point is below the theoretical capability, operating the wind turbine to generate power according to the power set-point, including operating the wind turbine according to a set-point rotor speed and a set-point generator torque predefined for the power set-point, the set-point rotor speed being outside the exclusion bands; and
wherein when the power set-point is above the theoretical capability, operating the wind turbine according to the predefined power curve until a first wind speed, and transitioning to the power set-point for wind speeds above the first wind speed.
2. The method of claim 1 , wherein the set-point rotor speed is in one or more selected speed sub-ranges defined between the exclusion bands.
3. The method of claim 2 , wherein the set-point rotor speed is one of a limited number of predefined rotor speeds.
4. The method of claim 3 , wherein the limited number of predefined rotor speeds includes between two and eight predefined rotor speeds.
5. The method of claim 3 , wherein for each speed sub-range, a power set-point is between a minimum power set-point and a maximum power set-point, wherein the maximum power set-point for a first speed sub-range is equal to a minimum power set-point for a second of the speed sub-ranges.
6. The method according to claim 1 , wherein according to the predefined power curve, a set-point rotor speed is reached at the first wind speed, and the transitioning comprises maintaining the set-point rotor speed and varying the torque until the power set-point is reached at a second wind speed.
7. The method of claim 6 , further comprising varying the pitch angles of the blades to maintain the power set-point for wind speeds above the second wind speed.
8. The method according to claim 1 , wherein according to the predefined power curve, the power set-point is reached at the first wind speed, and the transitioning comprises maintaining the power and increasing the rotor speed and reducing the generator torque until the set-point rotor speed is reached at a second wind speed.
9. The method of claim 8 , further comprising varying the pitch angles of the blades to maintain the power set-point for wind speeds above the first wind speed.
10. The method of claim 1 , further comprising receiving the power set-point limitation from a central control system or from a grid operator.
11. A variable speed wind turbine comprising:
a rotor with a plurality of blades;
a generator operably connected with the rotor;
a wind turbine controller that controls a torque of the generator and a pitch angle of the blades;
the wind turbine controller further configured to:
operate the wind turbine according to a predefined power curve in the absence of a power set-point limitation, the predefined power curve defining combinations of the pitch angles of the blades and the generator torque as a function of a wind speed;
in an event of a power set-point limitation, operate the wind turbine according to the power set-point limitation, including determining whether the power set-point is below or equal to a theoretical capability of the wind turbine in accordance with prevailing wind conditions;
when the power set-point is below the theoretical capability, operate the wind turbine to generate power according to the power set-point,
wherein each power set-point is defined by a combination of a set-point rotor speed and a set-point generator torque, the set-point rotor speed being one of a limited number of predefined rotor speeds; and
when the power set-point limitation is above the theoretical capability, operating the wind turbine according to the predefined power curve until a first wind speed, and transitioning to the power set-point for wind speeds above the first wind speed.
12. The wind turbine of claim 11 , wherein the predefined rotor speeds have a plurality of associated power set-point ranges, and wherein none of the power set-point ranges overlap.