Wind power installation and method for operating a wind power installation

Abstract

A method for operating a wind power installation for generating electrical power from wind, wherein the wind power installation has an aerodynamic rotor with rotor blades of which the blade angle is adjustable, and the rotor can be operated at a variable rotor rotation speed. Furthermore, the wind power installation has a generator, which is coupled to the aerodynamic rotor, in order to generate an output power. Here, the output power is set depending on the wind in a partial-load mode in which the wind is so weak that the wind power installation cannot yet be operated at its maximum output power, an actual air density of the wind is detected and each blade angle is set depending on the rotor rotation speed and depending on the detected air density. A wind power installation is also provided.

Claims

1. A method for operating a wind power installation for generating electrical power from wind, wherein: the wind power installation has an aerodynamic rotor with a plurality of rotor blades, wherein blade angles of the plurality of rotor blades are adjustable, wherein the aerodynamic rotor is configured to be operated at a variable rotor rotation speed, and the wind power installation has a generator that is coupled to the aerodynamic rotor and is configured to generate an output power, the method comprising: setting the output power depending on wind in a partial-load mode in which the wind is so weak that the wind power installation cannot be operated at its maximum output power; determining an air density of the wind; and setting each blade angle of the plurality of rotor blades depending on the output power or the rotor rotation speed and depending on the air density, wherein the output power is dynamically set with a first time constant, wherein each blade angle of the plurality of rotor blades is dynamically set with a second time constant, and wherein the first time constant is selected to be smaller than the second time constant.

2. The method as claimed in claim 1, wherein determining the air density comprises measuring an air pressure and an air temperature outside of the wind power installation and calculating the air density from the air pressure and the air temperature.

3. The method as claimed in claim 1, wherein setting each blade angle comprises setting each blade angle depending on a pitch characteristic, wherein the pitch characteristic specifies, for the partial-load mode, the blade angle to be set as a function of the output power or the rotor rotation speed, wherein the pitch characteristic depends on the air density.

4. The method as claimed in claim 1, comprising storing a plurality of pitch characteristics, wherein one pitch characteristic is selected from amongst the stored pitch characteristics depending on the air density to be used for setting the blade angle.

5. The method as claimed in claim 1, wherein each blade angle of the plurality of rotor blades is increased as the air density decreases.

6. The method as claimed in claim 1, wherein in the partial-load mode, the output power is set by an operating characteristic which specifies the output power to be set depending on the rotor rotation speed, and wherein the output power depends on the air density.

7. The method as claimed in claim 6, wherein the output power depends on the air density such that for the purpose of taking into account different air densities, a plurality of operating characteristics are stored and one of the plurality of stored operating characteristics is selected depending on the air density.

8. A wind power installation comprising one or more controllers configured to execute the method as claimed in claim 1.

9. The method as claimed in claim 1, wherein the first and the second time constants are respectively the time constant of a delay element of a first order or a delay element of a second order.

10. A wind power installation for generating electrical power from wind, comprising: an aerodynamic rotor, wherein the aerodynamic rotor is configured to be operated at a variable rotor rotation speed; a plurality of rotor blades coupled to the aerodynamic rotor, wherein blade angles of the plurality of rotor blades are adjustable; a generator coupled to the aerodynamic rotor, wherein the generator is configured to generate an output power, wherein the generator is configured to generate the output power depending on wind in a partial-load mode in which the wind is so weak that the wind power installation cannot be operated at its maximum output power; and a controller configured to: determine air density of the wind based on one or more sensed qualities of air outside of the wind power installation, and set each blade angle depending on the output power or the rotor rotation speed and depending on the air density, wherein the output power is dynamically set with a first time constant, wherein each blade angle of the plurality of rotor blades is dynamically set with a second time constant, and wherein the first time constant is selected to be smaller than the second time constant.

11. The wind power installation as claimed in claim 10, comprising: a power controller configured to set the output power depending on the rotor rotation speed, a pitch controller configured to set a blade angle depending on the rotor rotation speed and the air density, and data memory configured to store blade angle settings depending on the rotor rotation speed and the air density.

12. The wind power installation as claimed in claim 11, wherein the data memory is configured to store air density-dependent pitch characteristics.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 schematically shows a perspective illustration of a wind power installation.

(2) FIGS. 2 and 3 each show a set of pitch characteristics.

(3) FIG. 4 shows a simplified control structure for carrying out setting of a blade angle in the partial-load mode depending on the output power and the detected air density.

DETAILED DESCRIPTION

(4) FIG. 1 shows a schematic illustration of a wind power installation according to the invention. The wind power installation 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 with three rotor blades 108 and a spinner 110 is provided on the nacelle 104. During operation of the wind power installation, the aerodynamic rotor 106 is made to rotate by the wind, and therefore an electrodynamic rotor of a generator, which is directly or indirectly coupled to the aerodynamic rotor 106, also rotates. The electric generator is arranged in the nacelle 104 and generates electrical energy. The pitch angle of the rotor blades 108 can be changed by pitch motors at the rotor blade roots 108b of the respective rotor blades 108.

(5) FIGS. 2 and 3 show, in principle, two different types of sets of characteristics. Both FIGS. 2 and 3 show the blade angle α, which can also be referred to as pitch or pitch angle, depending on the output power P. In both cases, there is initially a constant blade angle α, which can have the value of a fixedly prespecified partial load angle α.sub.T, at low powers. As the power P increases, it is proposed to then increase the blade angle α. In this case, different characteristics are provided for the blade angle depending on the air density ρ, said different characteristics therefore forming a set of characteristics. The two exemplary proposals of FIGS. 2 and 3 differ in respect of the set of characteristics.

(6) FIG. 2 shows a profile in which the blade angle is increased at all the more smaller powers P, the lower the air density ρ. In this case, the solid curve shows the profile of the blade angle for a normal air density ρ.sub.0, for which a value of 1.225 kg/m.sup.3 is taken as a basis. For this normal air density, the blade angle increases starting from a power P.sub.0. The dotted characteristic shows a profile for a lower air density ρ.sub.1 and the dashed-and-dotted characteristic shows a profile for an even lower air density ρ.sub.2. According to these two characteristics, the blade angle is already increased for a lower output power than P.sub.0. The value of ρ.sub.2 can be 1 kg/m.sup.3 and that of ρ.sub.1 can be 1.1 kg/m.sup.3 for example.

(7) It can be seen that the characteristics of FIG. 2 have been selected such that they run approximately parallel to one another.

(8) In the embodiment of FIG. 3, it is proposed to also increase the blade angles for different air densities ρ.sub.0, ρ.sub.1 and ρ.sub.2 starting from a power P.sub.0. However, a profile which is all the more steeper the lower the air density is then proposed.

(9) The values for P0, ρ.sub.0, ρ.sub.1 and ρ.sub.2 can be the same for both FIGS. 2 and 3. The two FIGS. 2 and 3 also show a profile of the blade angle characteristics and therefore of the sets of characteristics up to the rated power P.sub.N.

(10) The control structure or controller of FIG. 4 shows, in an illustrative manner, a generator 401 and a rotor blade 403 which can be adjusted by means of a pitch drive 405. These elements are only symbolically illustrated and it is possible for, for example, three rotor blades 403 which each have a pitch drive 405 and are driven by the wind and as a result drive the generator 401 to be provided.

(11) The generator 401 is provided as an externally excited synchronous generator here and, in this structure, is driven by means of a current controller 407 which controls the excitation current I.sub.E. As a result, power control is performed, this being only simply indicated here and it being possible for this to also be performed differently. Other generators can also be provided. The current controller 407 also represents other power control arrangements here. Said current controller receives a power value P as a prespecification and this power value P is given by a rotation speed/power characteristic which is stored in the characteristic block 409 of the controller. The characteristic block 409 outputs a power value P based on the rotation speed/power characteristic depending on the rotation speed n of the rotor to which the rotor blades 403 belong.

(12) The power value P is not only input into the current controller in order to control the power of the generator 401 by means of the power controller 407, but rather the power value P is also used as an input variable for a blade angle prespecification unit 411. The blade prespecification unit 411 determines a blade angle α to be set depending on the power P. In this case, the output power of the wind power installation, that is to say the power actually output by the wind power installation, is preferably used as the input variable. However, for the sake of simplicity and for illustration purposes, the output power can be equated to the power P which the characteristic block 409 outputs. The output power is set with high dynamics, so that this simplification for illustration is permissible and so that there are no vibration problems or hazards between the power setting on the one hand and the blade angle adjustment on the other hand.

(13) The blade angle prespecification unit 411 of the controller has a plurality of characteristic blocks, of which three characteristic blocks K1, K2 and K3 are shown here by way of example. Each of these characteristic blocks has a power-dependent blade angle characteristic, which blade angle characteristics together form a set of characteristics and, respectively, provide a set of characteristics for selection. It is now proposed to select one of the characteristic blocks and therefore one of the characteristics depending on the air density ρ. For this purpose, the air density r can be detected, for example, by a measurement unit 413.

(14) The blade angle α can therefore be set depending on the output power P and the air density ρ. For this purpose, the output power P forms the input variable for the blade prespecification unit 411 and the air density ρ is input by way of a matched characteristic being selected depending on the air density ρ. The blade angle α ascertained in this way is then passed to the pitch drive 405 in order to correspondingly set the respective rotor blade 403.

(15) Therefore, a solution has been proposed in order to improve the prior art in which rotor blades are designed such that air can flow around them at a normal air density of ρ=1.225 kg/m.sup.3 at all operating points of the installation without separation. It has been found that installations are now increasingly being planned at locations at which the air density is, sometimes considerably, below the standard air density. This leads to flow separations possibly occurring due to the increase in the effective angle of attack on the rotor blade, this in turn possibly leading to substantial power losses. In this case, it has been found that the smaller the air density becomes, the more the effective angles of attack on the rotor blade increase and the more likely it is that power-reducing flow separations will occur. The flow separations can be avoided by pitching of the rotor blades. It is proposed here that pitching of the rotor blades is matched to the air density. Accordingly, it is proposed that the pitch angle to be set is now a function of the electrical output power, specifically the output power, and the air density. It is therefore proposed that not only a function of the electrical output power forms the basis for setting of the blade angle. It is therefore proposed to measure the air pressure and the temperature at the wind power installation and to calculate the air density therefrom, so that the respective pitch angle can be determined with the aid of a stored function.

(16) Ultimately, the increase in the annual yields of a pitch-controlled, variable-speed wind power installation can therefore also be achieved by the proposed use of pitch characteristics which are matched to the air density of the location.