Method for controlling a wind power installation at different operating points

Abstract

A method for controlling a wind power installation is provided. The method includes operating the installation at a normal operating point at which the installation is not operated in a throttled fashion if there is no request for throttling, and operating the installation at a throttled operating point, in response to a throttle request, with output power which is throttled in comparison with the normal operating point. The method includes changing the operation from the throttled operating point to a reserve operating point at which the installation is operated with higher output power in response to a power increase request. The throttled operating point has a higher tip speed ratio than that of the reserve operating point and is positioned on an associated iso-characteristic curve in the λθ diagram having, at the throttled operating point, a negative characteristic curve gradient.

Claims

1. A method for controlling a wind power installation, the method comprising: determining whether a throttle request has been received, in response to determining that a throttle request has not been received, operating the wind power installation at a normal operating point at which the wind power installation is operated at a rated power of the wind power installation, wherein the wind power installation is operated in a partial load range when sufficient wind is not present to operate the wind power installation at the rated power of the wind power installation, wherein the wind power installation includes a rotor having a plurality of rotor blades, each rotor blade is adjustable to a plurality of blade angles, and wherein the rotor is configured to be operated with a variable rotational speed, in response to determining that the throttle request has been received, operating the wind power installation at a throttled operating point at which the wind power installation is operated with an output power that is throttled in comparison with the normal operating point; receiving a power increase request, and in response to receiving the power increase request, operating the wind power installation at a reserve operating point at which the wind power installation is operated with a higher output power in comparison with the output power at the throttled operating point, wherein the throttled operating point has a higher tip speed ratio than the reserve operating point, wherein each operating point of the normal operating point, the throttled operating point, and the reserve operating point is defined by a blade angle and a tip speed ratio and is configured to be represented by a tip speed ratio/blade angle diagram (λθ diagram) in which the tip speed ratio is plotted against the blade angle, wherein each operating point of the normal operating point, the throttled operating point, and the reserve operating point is represented in the λθ diagram as a value pair including the blade angle and the tip speed ratio, wherein each operating point of the normal operating point, the throttled operating point, and the reserve operating point is associated with a power coefficient, wherein each operating point of the normal operating point, the throttled operating point, and the reserve operating point has a same power coefficient and is configured to be represented by an iso-characteristic curve in the λθ diagram, and wherein the throttled operating point is positioned on an associated iso-characteristic curve in the λθ diagram, and the associated iso-characteristic curve has, at the throttled operating point, a negative characteristic curve gradient at which the tip speed ratio decreases as the blade angle increases.

2. The method as claimed in claim 1, wherein the negative characteristic curve gradient, at the throttled operating point, has an absolute value of at least 0.5/1°.

3. The method as claimed in claim 1, wherein the reserve operating point has: a lower output power than the normal operating point, and/or a lower tip speed ratio than the throttled operating point.

4. The method as claimed in claim 1, wherein the reserve operating point has a higher tip speed ratio than the normal operating point.

5. The method as claimed in claim 1, wherein the throttled operating point and/or the reserve operating point is selected as a function of: a distance between two iso-characteristic curves of the λθ diagram at the throttled operating point or at the reserve operating point, and/or a gradient of the power coefficient of the throttled operating point or a gradient of the power coefficient of the reserve operating point.

6. The method as claimed in claim 1, wherein the throttled operating point and/or the reserve operating point are selected such that a derivative of the power coefficient of the throttled operating point or a derivative of the power coefficient of the reserve operating point according to a particular blade angle, exceeds a respective minimum value.

7. The method as claimed in claim 1, wherein: the wind power installation is characterized by a characteristic curve diagram including iso-characteristic curves of the λθ diagram, the characteristic curve diagram is defined as a standardized characteristic curve diagram, in the standardized characteristic curve diagram, a first sub-region is formed in which blade angles are greater than blade angles of the normal operating point, and the iso-characteristic curves in the first sub-region have a negative characteristic curve gradient in which the tip speed ratio decreases as the blade angle increases, each operating point in the standardized characteristic curve diagram is characterized by a gradient value quantifying a maximum gradient of the power coefficient of the respective operating point in the standardized characteristic curve diagram, in the first sub-region of the standardized characteristic curve diagram, an operating point with a maximum gradient value is present for each iso-characteristic curve, and wherein a gradient characteristic curve is represented and connects operating points with maximum gradient values, the throttled operating point and/or the reserve operating point are selected such that they each are positioned on the gradient characteristic curve, and/or in a gradient band including the gradient characteristic curve, the gradient band has: an upper band limit which is higher than the gradient characteristic curve by an upper tip speed ratio difference, and a lower band limit which is lower than the gradient characteristic curve by a lower tip speed ratio difference.

8. The method as claimed in claim 7, wherein: the upper and lower tip speed ratio differences have maximum values of 2, the upper and lower tip speed ratio differences have maximum values of 1, the upper tip speed ratio difference has a maximum value of 1, or the lower tip speed ratio difference has a maximum value of 4.

9. The method as claimed in claim 1, wherein the wind power installation has: at the throttled operating point: a first output power level, a first rotational energy level, and a first blade angle, and at the reserve operating point: a second output power level, a second rotational energy level, and a second blade angle, wherein the first output power level is lower than the second output power level, and a difference between the second output power level and the first output power level forms a differential output power level, wherein the first rotational energy level is higher than the second rotational energy level, and a difference between the first and second rotational energy levels forms a difference rotational energy level, wherein a blade adjustment time is used to adjust the plurality of rotor blades from the first blade angle to the second blade angle, wherein a product of the differential output power level and the blade adjustment time multiplied by 50% forms a characteristic differential energy level, and wherein the throttled operating point and/or the reserve operating point are selected such that the difference rotational energy level is above or below the characteristic differential energy level by a maximum percentage deviation value.

10. The method as claimed in claim 9, wherein the maximum percentage deviation value is 60%, 40% or 20%.

11. The method as claimed in claim 1, further comprising operating the wind power installation at an intermediate operating point, wherein a power coefficient of the intermediate operating point is the same as a power coefficient of the throttled operating point or different from the power coefficient of the throttled operating point by less than 20%.

12. The method as claimed in claim 11 further comprising: operating the wind power installation at the throttled operating point.

13. The method as claimed in claim 1, wherein: the throttle request is as an external signal received by a data interface of a controller, and/or the power increase request is a signal indicative of a state of an electric supply network, wherein the state is sensed by the wind power installation.

14. The method as claimed in claim 13, wherein the signal indicative of the state of the electric supply network is a function of a sensed network frequency of the electric supply network.

15. The method as claimed in claim 1, wherein the wind power installation is operated for a longer time period at the throttled operating point than at the reserve operating point.

16. The method as claimed in claim 15, the wind power installation is operated at least 20 times as long at the throttled operating point than at the reserve operating point.

17. A wind power installation, comprising: a rotor having a plurality of rotor blades having adjustable blade angles, wherein the rotor is capable of being operated with a variable rotational speed, wherein the wind power installation is capable of being operated in a partial load range in which sufficient wind is not present to operate the wind power installation with a rated power of the wind power installation, and a controller configured to: operate the wind power installation in the partial load range; determine whether a throttle request has been received; in response to determining that a throttle request has not been received, operate the wind power installation at a normal operating point at which the wind power installation is operated at a rated power of the wind power installation; and in response to receiving the throttle request, operate the wind power installation at a throttled operating point at which the wind power installation is operated with an output power that is throttled in comparison with the normal operating point; receive a power increase request; and in response to receiving the power increase request, operate the wind power installation at a reserve operating point at which the wind power installation is operated with a higher output power in comparison with the output power at the throttled operating point, wherein each operating point of the normal operating point, the throttled operating point, and the reserve operating point is defined by a blade angle and a tip speed ratio and is configured to be represented by a tip speed ratio/blade angle diagram (λθ diagram) in which the tip speed ratio is plotted against the blade angle, wherein each operating point of the normal operating point, the throttled operating point, and the reserve operating point is represented in the λθ diagram as a value pair including the blade angle and the tip speed ratio, wherein each operating point of the normal operating point, the throttled operating point, and the reserve operating point is associated with a power coefficient, wherein each operating point of the normal operating point, the throttled operating point, and the reserve operating point has a same power coefficient and is configured to be represented by an iso-characteristic curve in the λθ diagram, wherein the throttled operating point has a higher tip speed ratio in comparison with the reserve operating point, and wherein the throttled operating point is positioned on an associated iso-characteristic curve in the λθ diagram, and the associated iso-characteristic curve has, at the throttled operating point, a negative characteristic curve gradient at which the tip speed ratio decreases as the blade angle increases.

18. The wind power installation as claimed in claim 17, wherein the controller comprises a data interface configured to receive an external signal indicative of the throttle request; and wherein the wind power installation includes a sensor configured to sense and evaluate a state of an electric supply network and provide a signal indicative of the state of the electric supply network to the controller, the signal being indicative of the power increase request.

19. The wind power installation as claimed in claim 17, comprising: a control memory configured to: store control information for operating the wind power installation; and/or store the normal, throttled, and reserve operating points that are dependent on a wind speed, wherein the normal operating point, the throttled operating point, and the reserve operating point are stored for a plurality of wind speeds.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention may now be explained below in more detail on the basis of exemplary embodiments and with reference to the accompanying figures:

(2) FIG. 1 shows a wind power installation in a perspective illustration,

(3) FIG. 2 shows a power/rotational speed diagram for different wind speeds,

(4) FIG. 3 shows a λθ-diagram, and

(5) FIG. 4 shows a time diagram illustrating a transition from a throttled operating point to a reserve operating point.

DETAILED DESCRIPTION

(6) FIG. 1 shows a schematic illustration of a wind power installation. 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. The aerodynamic rotor 106 is placed in a rotational motion by the wind during the operation of the wind power installation, and said rotor 106 therefore also rotates an electrodynamic rotor of a generator, which rotor is coupled directly or indirectly to the aerodynamic rotor 106. The electrical 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 on the rotor blade roots 109 of the respective rotor blades 108.

(7) The wind power installation 100 has here an electrical generator 101 which is indicated in the nacelle 104. Electrical power can be generated by means of the generator 101. A feed unit 105 is provided for feeding electrical power and can be embodied in particular as a power inverter. In this way, a three-phase feed current and/or a three-phase feed voltage can be generated according to amplitude, frequency and phase, to be fed into a network connection point PCC. This can also take place directly or else together with further wind power installations in a wind park. In order to control the wind power installation 100 and also the feed unit (inverter) 105 an installation controller 103 is provided. The installation controller 103 can also receive specification values from the outside, in particular from a central wind farm computer.

(8) FIG. 2 shows a diagram in which characteristic curves, which show the relationship between the rotor power P and rotor rotational speed n, are shown for different wind speeds. In this context, characteristic curves k.sub.3-k.sub.13 are illustrated. The index relates in each case to the associated value of the wind speed, specifically 3 m/s for k.sub.3 to 13 m/s for k.sub.13. It is apparent that as the rotational speed n increases on each of the characteristic curves k.sub.3-k.sub.13 the power P which can be generated firstly increases until a maximum is reached. Starting from the maximum, the power P then decreases again as the rotational speed increases. For optimum operation, that is to say for an optimum power coefficient and therefore maximum power generation the wind power installation is respectively operated at the maximum of the characteristic curves.

(9) This is shown as an optimum operating characteristic curve 200 in FIG. 2. However, the wind power installation cannot be operated with randomly high rotational speeds but rather should not exceed a rated rotational speed n.sub.N. This rated rotational speed n.sub.N is shown in the diagram. For wind speeds of 10 m/s, the maximum of the respective characteristic curve, that is to say the characteristic curve k.sub.10, is approximately in the region of the rated rotational speed. In the case of characteristic curves for relatively high wind speeds, that is to say on the characteristic curves k.sub.11-k.sub.13, the maximum values occur at relatively high rotational speeds and there is correspondingly an inflection of the optimum operating characteristic curve when the maximum of the characteristic curve k.sub.10 is reached, and said operating characteristic curve proceeds perpendicularly from there. From there, the wind power installation is no longer operated in the optimum operating mode, specifically in order to protect it against overloading.

(10) The optimum operating characteristic curve 200 therefore relates, up to this inflection in the characteristic curve k.sub.10, to the partial load range in which the wind power installation cannot yet generate maximum power. The perpendicular range is in this respect a reduced characteristic curve 220.

(11) It is therefore in particular realized that both an increase in the rotational speed and a decrease in the rotational speed are therefore considered in order to reduce the power at low wind speeds. It has particularly been realized that as a result a degree of freedom in the selection of a throttled operating point can be utilized.

(12) FIG. 3 shows a portion of a λθ diagram. The tip speed ratio λ is illustrated on the ordinate therein, and the blade angle θ is illustrated on the abscissa with the unit degrees (°). The tip speed ratio λ without units is therefore plotted against the blade angle θ. In the λθ diagram iso-characteristic curves I.sub.0,45 to I.sub.0,00 are additionally shown. The index respectively specifies the associated power coefficient of the respective characteristic curve here. The power coefficient of the iso-characteristic curve I.sub.0,45 is therefore 0.45. The iso-characteristic curves are entered here initially for a Cp value of 0.45 in uniform 0.05 increments up to the Cp value of 0.05, and as a last value of 0.00. The difference in the Cp value between two adjacent iso-characteristic curves is therefore always 0.05.

(13) In addition, an installation operating characteristic curve 300 is entered in the diagram. This installation operating characteristic curve 300 represents the totality of the operating points of the wind power installation which are set according to the wind speed if there is no particular throttling request present. An optimal operating point 302 lies as it were in the center of the iso-characteristic curve I.sub.0,45 for a Cp value of 0.45. The Cp value of the optimum operating point 302 may be slightly higher. Although the installation operating characteristic curve 300 is a characteristic curve along which the operating points can change, it can nevertheless be the case that at the optimum operating point 302 the operation of the wind power installation is carried out for a relatively large range of wind speeds. In other words, a very large number of operating points for different wind speeds may as it were occur one on top of the other at the optimum operating point 302.

(14) Nevertheless, this optimum operating point 302 can vary with the wind speed. Owing to boundary conditions it is to be expected that at very low wind speeds, for example below 5 m/s, a relatively high tip speed ratio is appropriate. Correspondingly, a small change in the blade angle θ can then be appropriate. In order to illustrate this, a suboptimum operating point 304 is entered for low wind speeds, or the branch of the installation operating curve 300 in the vicinity of the suboptimum operating point 304 generally stands for operation at low wind speeds.

(15) At high wind speeds, the tip speed ratio will decrease toward the end of the partial load range and beyond, as the wind speed increases. When the partial load range is exited, the blade angle θ is then increased in order to reduce the power of the wind power installation. This is characterized by the reduced characteristic curve branch 306.

(16) There are many options for selecting a throttled operating point in the case of a throttling request, that is to say when the wind power installation is to continuously output less power in the partial load range than it could generate from the wind. Initially, ideally starting from the optimum operating point 302 an operating point is found at which the power coefficient is correspondingly lower than in the case of the optimum operating point 302. If the wind power installation is intended to generate, for example, approximately half as much power at the throttled operating point as at the optimum operating point, it is proposed that the throttled operating point be selected on the iso-characteristic curve I.sub.0,25. Correspondingly, a throttled operating point 308 is entered as an illustrative example in the diagram in FIG. 3.

(17) Furthermore, a reserve operating point 310 is provided which has a higher output power level than the throttled operating point 308, and therefore would be selected, for example, on the iso-characteristic curve I.sub.0,40 for a power coefficient of 0.4.

(18) It is now proposed that the throttled operating point 308 have an increased tip speed ratio in comparison with the reserve operating point 310. Correspondingly, these two operating points 308 and 310 are entered in the diagram in FIG. 3. If there is then a changeover from the throttled operating point 308 to the reserve operating point 310, specifically in reaction to a power increase request, the rotational speed for this is reduced somewhat because the tip speed ratio λ, must be reduced for this. Assuming an identical wind speed, the reduction in the tip speed ratio is therefore a reduction in the rotational speed. As a result, kinetic energy can be released and as a result a power increase can be achieved immediately, said increase already starting before the reserve operating point 310 has been reached.

(19) It is also apparent from the diagram in FIG. 3 that the throttled operating point 308 lies on an associated iso-characteristic curve, that is to say the iso-characteristic curve I.sub.0,25, which namely has this desired Cp value of 0.25, and that at this throttled operating point 308 this iso-characteristic curve I.sub.0,25 has a negative characteristic curve gradient on which the tip speed ratio decreases as the blade angle increases. The gradient of the iso-characteristic curve I.sub.0,25 is approximately −2.2/1° here.

(20) From the diagram in FIG. 3 it is apparent that the throttled operating point 308 resulting from the proposed selection, specifically including the selection according to which the characteristic curve gradient is negative at the throttled operating point, is not located in the region in which the installation operating characteristic curve 308 occurs or could occur at low wind speeds. It is also apparent that at these values of a higher tip speed ratio than the reserve operating point but a negative characteristic curve gradient here the characteristic curves are very close to one another. The illustrated distance in FIG. 3 between the throttled operating point 308 and the reserve operating point 310 is as a result comparatively small. In order to move from the iso-characteristic curve I.sub.0,25 to the iso-characteristic curve I.sub.0,4 in the selected range, only a blade adjustment of less than 2° is necessary. This rapid change capability can be provided by means of the proposed selection of the throttled operating point and of the reserve operating point, in particular by means of the selection of the throttled operating point with respect to the reserve operating point.

(21) In addition, a gradient characteristic curve 320 with an upper band limit 321 and a lower band limit 322 is entered in FIG. 3. Both band limits are entered by dashed lines and different values for the distance between the band limits have been selected here so that the gradient characteristic curve in the band lies further upward with respect to the upper band limit.

(22) FIG. 4 illustrates a preferred selection of the throttled operating point with respect to the reserve operating point taking into account the kinetic energy of both operating points. For this purpose, FIG. 4 illustrates the plurality of time profiles, specifically in four individual diagrams. Each diagram uses the same time axis. FIG. 4 illustrates here the changeover from a throttled operating point to a reserve operating point. This changeover starts at the time t.sub.1, at which the throttled operating point is exited and ends at the time t.sub.2 when the reserve operating point is reached. The illustrated changeover can relate to a changeover of the throttled operating point 308 to the reserve operating point 310 according to FIG. 3.

(23) In order to change the throttled operating point to the reserve operating point, the blade angle is adjusted somewhat linearly, for example, from 6° to 4°. This is illustrated in the lower diagram I, which can be referred to as a diagram of the blade angle profile. It is assumed that the blade angle is adjusted with the maximum adjustment speed, and therefore for this the blade adjustment time T.sub.θ, that is to say the difference between t.sub.2 and t.sub.1, is required.

(24) At the same time, the rotational speed n decreases, in an idealized approximately linear fashion, from the value n.sub.1 at the time t.sub.1, that is to say the rotational speed of the throttled operating point, to the rotational speed n.sub.2 at the time t.sub.2, that is to say the rotational speed of the reserve operating point. This is illustrated in the diagram II, which therefore forms a diagram for representing the rotational speed profile.

(25) The throttled operating point therefore has a lower output power level with the value P.sub.1, while the reserve operating point has an increased output power level with the value P.sub.2. Accordingly, the output power level P.sub.A increases from the value P.sub.1 to the value P.sub.2, specifically from the time t.sub.1 to the time t.sub.2.

(26) In this respect, the power which the wind power installation generates from the wind and outputs at the respective operating point is to be understood as the output power P.sub.A. The output power P.sub.A is also to be understood as that which is generated from the wind in the range between the times t.sub.1 and t.sub.2, that is to say in the transition range, when the changeover occurs between the throttled operating point and the reserve operating point.

(27) However, it is now proposed that the fed-power be increased initially more quickly in the transition range, in order to reach the value P.sub.2 as quickly as possible. Such a power level can be referred to as an instantaneous power level P.sub.I and is entered as a dashed line in the third diagram III. This third diagram III therefore denotes a diagram for the profile of the power.

(28) In an ideal case, it is possible to extract so much power from the kinetic energy of the rotor of the wind power installation at the time t.sub.1, or directly thereof, that the power increases immediately to the value P.sub.2. Then, more power is fed into the electric supply network than the output power P.sub.A which is present. This output power P.sub.A approaches, however, the instantaneous power level, P.sub.I slowly and reaches it at the time t.sub.2.

(29) From the idealized increase in the instantaneous power P.sub.I in comparison with the output power P.sub.A in the time from t.sub.1 to t.sub.2 an approximately triangular region is therefore obtained which is illustrated in a hatched fashion in this diagram III. Its surface content corresponds to an energy level which is referred to as a characteristic differential energy level ΔE.sub.c.

(30) In addition, in the fourth diagram IV the profile of the kinetic energy E.sub.k of the wind power installation is illustrated. The profile of the kinetic energy E.sub.k between the times t.sub.1 and t.sub.2 corresponds approximately to the negative integral of the power differential range which is illustrated in a hatched fashion in diagram III. In an ideal case, the difference between the initial kinetic energy E.sub.1 minus the kinetic energy E.sub.2 which is reached at the time t.sub.2 corresponds to the characteristic differential energy level ΔE.sub.c.

(31) It is to be noted that this FIG. 4 serves for illustrative purposes and represents an idealized case. It is of course to be particularly noted that when there is a very strong increase in the instantaneous power P.sub.I shortly after the time t.sub.1 with the correspondingly strongly decreasing energy value of the kinetic energy E.sub.k, the rotational speed n would also decrease strongly, as illustrated. This is indicated in the second diagram II by a dotted line and denoted as n′.

(32) A correspondingly more rapid drop in the rotational speed could also have effects on the profile of the output power P.sub.A in the diagram III. However, a more rapid drop in the rotational speed n would not necessarily cause the output power P.sub.A to increase correspondingly more quickly at the same time, because from FIG. 3 it is apparent that a relatively fast drop in the rotational speed, that is to say a relatively fast drop in the tip speed ratio, would not necessarily bring about a faster increase in the power coefficient.

(33) It has therefore been realized that the characteristic differential energy level ΔE.sub.c can be calculated in good approximation from the product of the different output power, that is to say P.sub.2 minus P.sub.I, and the blade adjustment time T.sub.θ and additionally multiplied by ½. Accordingly, it is proposed that the throttled operating point and/or the reserve operating point be selected such that the differential rotational energy level be selected approximately with the order of magnitude of the characteristic differential energy level ΔE.sub.c.

(34) The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.