METHOD FOR OPERATING A WIND TURBINE IN THE EVENT OF A GRID FAULT

Abstract

Provided is a method for operating a wind turbine having a generator and a rotor with rotor blades. The method includes generating electrical power from wind using the generator, using a first part of the generated power as an auxiliary component for supplying auxiliary devices of the turbine used for operating the turbine, where the auxiliary component varies up to a limit. The method includes feeding a second part of the generated electrical power into a grid as a feed-in component, checking the grid for a grid fault that does not allow feeding power into the grid and continuing the operation of the turbine when the fault is detected. The generation of power from wind is reduced to a cut-back power that corresponds to the limit the auxiliary component for operating the auxiliary devices is used from the cut-back power and remaining residual power of the cut-back power is consumed.

Claims

1. A method for operating a wind turbine having a generator and an aerodynamic rotor with a plurality of rotor blades, the method comprising: generating electrical power from wind using the generator; using a first portion of the generated electrical power as an auxiliary power component for supplying auxiliary devices of the wind turbine that are used for operating the wind turbine, wherein the auxiliary power component is variable and has an upper auxiliary power limit; feeding a second portion of the generated electrical power into an electrical supply grid as a feed-in power component; checking the electrical supply grid for a grid fault that hinders feeding of the second portion of the generated electrical power of the wind turbine into the electrical supply grid; detecting the grid fault; and continuing to operate the wind turbine in response to detecting the grid fault including at least; cutting back the generation of electrical power from the wind to a cut-back power, wherein the cut-back power corresponds to the upper auxiliary power limit or is greater than the upper auxiliary power limit; drawing the auxiliary power component for supplying the auxiliary devices from the cut-back power; and consuming residual power of the cut-back power that remains after drawing the auxiliary power component.

2. The method as claimed in claim 1, comprising: feeding in the second portion of the generated electrical power using an inverter with a DC link; in response to detecting the grid fault, transferring the cut-back power or a portion of the cut-back power to the DC link without the inverter feeding power into the electrical supply grid; and removing power from the DC link by a chopper circuit into a chopper resistor for conversion into heat.

3. The method as claimed in claim 1, comprising: determining the upper auxiliary power limit based on an operating point of the wind turbine; determining the upper auxiliary power limit based on system properties of the wind turbine; and/or identifying the upper auxiliary power limit in a predetermined measuring time period before an occurrence of the grid fault.

4. The method as claimed in claim 1, comprising: in response to detecting the grid fault, continuing to transfer the auxiliary power component by the generator to the auxiliary devices for supplying the auxiliary devices without additional storage buffering in an electrical store.

5. The method as claimed in claim 1, comprising: in response to detecting the grid fault, continuing to supply the auxiliary power component to the auxiliary devices without change; and/or in response to detecting the grid fault, refraining from cutting back the auxiliary devices.

6. The method as claimed in claim 1, comprising: in response to detecting the grid fault, disconnecting the wind turbine from the electrical supply grid.

7. The method as claimed in claim 1, comprising: in response to detecting the grid fault and following detecting the grid fault, continuing to operate the wind turbine without feeding the feed-in power component into the electrical supply grid until the grid fault is rectified; and resuming feeding the feed-in power component into the electrical supply grid without delay, and/or running up the electrical supply grid or a portion of the electrical supply grid again in a black starting mode.

8. The method as claimed in claim 1, wherein the auxiliary devices include at least one auxiliary device from a list including: one or more blade adjustment devices for adjusting a blade angle of the rotor blades, one or more azimuth adjusting devices for adjusting a nacelle alignment of the wind turbine, an exciter generator for generating an exciter current of the generator if the generator is formed as a separately excited synchronous generator, ventilating devices for ventilating the wind turbine. first cooling devices for cooling the generator, second cooling devices for cooling semiconductor components of an inverter and semiconductor components of chopper circuit, and a controller for controlling the operation of the wind turbine.

9. The method as claimed in claim 1, wherein: the cut-back power is generated at a level that provides at least one temporary power component for operating at least one auxiliary device used temporarily, and the at least one temporary power component is used for operating the at least one auxiliary device used temporarily, or the at least one temporary power component is removed using a chopper circuit.

10. A wind turbine, comprising: an aerodynamic rotor having a plurality of rotor blades; a generator configured to generate electrical power from wind; one or more auxiliary devices configured to: perform auxiliary functions for operation of the wind turbine; use a first portion of the generated electrical power as an auxiliary power component, the auxiliary power component being variable and having an upper auxiliary power limit; an inverter configured to feed a second portion of the generated electrical power into an electrical supply grid, the second portion forming a feed-in power component; and a controller configured to: check the electrical supply grid for a grid fault that hinders feeding the second portion of the generated electrical power of the wind turbine into the electrical supply grid; detect the grid fault continue operating the wind turbine in response to detecting the grid fault; reduce the generated electrical power from the wind to a cut-back power corresponding corresponds to the upper auxiliary power limit or being greater than the upper auxiliary power limit; cause the auxiliary power component for supplying the auxiliary devices to be drawn from the cut-back power; and cause residual power of the cut-back power that remains after drawing the auxiliary power component to be consumed.

11. (canceled)

12. The wind turbine as claimed in claim 10, wherein: the inverter has a DC link, and the wind turbine includes a chopper circuit coupled to the DC link and including a chopper resistor, wherein: in response to detecting the grid fault, the cut-back power, or a portion of the cut-back power is transferred to the DC link without the inverter feeding the second portion of the generated electrical power into the electrical supply grid, and power from the DC link is removed using the chopper circuit into the chopper resistor for conversion into heat.

13. The wind turbine as claimed in claim 10, wherein the auxiliary devices include at least one auxiliary device from a list including: one or more blade adjustment devices for adjusting a blade angle of the rotor blades, one or more azimuth adjusting devices for adjusting a nacelle alignment of the wind turbine, an exciter generator for generating an exciter current of the generator if the generator is formed as a separately excited synchronous generator, ventilating devices for ventilating the wind turbine, first cooling devices for cooling the generator, second cooling devices for cooling semiconductor components of the inverter and semiconductor components of a chopper circuit, and the controller.

14. The method as claimed in claim 1, wherein the second portion of the generated electrical power is a difference between the generated electrical power and the first portion of the generated electrical power.

15. The method as claimed in claim 1, wherein consuming the residual power of the cut-back power that remains after drawing the auxiliary power component includes converting the residual power into heat.

16. The method as claimed in claim 2, wherein the removed power is the residual power or a portion of the residual power.

17. The method as claimed in claim 2, comprising: removing, by the chopper circuit, the power from the DC link based on a sensed link voltage; and/or supplying at least one auxiliary device with the power from the DC link.

18. The method as claimed in claim 4, comprising: in response to detecting the grid fault, continuing to transfer the auxiliary power component to the auxiliary devices without additional storage buffering that is longer than 100 millisecond (ms).

19. The method as claimed in claim 7, comprising: controlling a link voltage of a DC link of an inverter to a predetermined standby voltage value using a chopper circuit during the grid fault.

20. The method as claimed in claim 9, wherein the at least one auxiliary device is one or more blade adjusting devices for adjusting a blade angle of the rotor blades or one or more azimuth adjusting devices for adjusting a nacelle alignment of the wind turbine.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0072] The invention is explained in more detail below by way of example on the basis of exemplary embodiments with reference to the accompanying figures.

[0073] FIG. 1 shows a wind turbine in a perspective representation,

[0074] FIG. 2 shows a functional part of a wind turbine in a schematic representation,

[0075] FIG. 3 shows a diagram for explaining a proposed power control.

DETAILED DESCRIPTION

[0076] FIG. 1 shows a wind turbine 100 with a tower 102 and a nacelle 104. Arranged on the nacelle 104 is a rotor 106 with three rotor blades 108 and a spinner 110. During operation, the rotor 106 is set in a rotary motion by the wind, and thereby drives a generator in the nacelle 104.

[0077] FIG. 2 particularly shows a power train to illustrate the flow of power from the generator to the grid feed-in. For this purpose, the wind turbine has an aerodynamic rotor 206 with a number of rotor blades 208. During operation, this rotor 106 is consequently driven by the wind and thereby drives a generator 220.

[0078] The rotor 206 has rotor blades 208 that can be changed in their angle of attack. The adjustability of the rotor blades 208 is indicated by way of example by two arrows. For the adjustment, a pitch drive 222 is used each rotor blade 208 and one of these is schematically depicted in FIG. 2 as a corresponding block. This allows the angle of attack of the rotor blades 208 to be changed, in order in this way to change the aerodynamic effectiveness of the rotor 206, with respect to the wind. For example, the rotor blades 208 may be partially or completely turned out of the wind by means of the pitch drives 222, so that as a result the rotor 206 can take less power from the wind. In continuous operation, the pitch drives 222 can be supplied with power that can be taken from the power generated by the generator 220.

[0079] The generator 220 is formed here as a separately excited synchronous generator and has as a preferred embodiment a six-phase electrical configuration. Accordingly, two three-phase stator windings are present and the generator 220 consequently generates a six-phase stator current, which is fed to a rectifier 224.

[0080] The rectifier 224 rectifies the stator current thus obtained and passes it to a first DC link 226. The first DC link 226 has a first link capacitor 228. This first link capacitor 228 may bring about a voltage smoothing or voltage stabilization in the first DC link 226.

[0081] The first DC link 226 also supplies an exciter generator 230, which generates an exciter current or an exciter voltage, and consequently generates an exciter power for the separately excited synchronous generator 220 and correspondingly feeds it to the generator 220.

[0082] It can also be seen here from FIG. 2 that the exciter generator 230 also takes its power component from the power that the generator 220 generates from the wind.

[0083] Also provided is a step-up converter 232, which can raise the link voltage of the first DC link 226, particularly when there is low power generation by the generator 220. The DC voltage thus increased is then provided on the second DC link 234 by the step-up converter 232. Instead of the rectifier 224, first DC link 226, step-up converter 232 and second DC link 234, a controlled rectifier could also be provided, which provides the generator power that is generated directly with the desired voltage at the second DC link 234, though the second DC link would then be the only DC link. The exciter generator 230 can then be supplied with power by this single DC link. Such a controlled rectifier would consequently substantially replace the rectifier 224, first DC link 226 and step-up converter 232.

[0084] The second DC link 234 has a second link capacitor 236, which has a substantially quite similar function to the first link capacitor 228 of the first DC link 226.

[0085] The DC voltage is inverted by the second DC link 234, by an inverter 238, and is output via a grid filter 240 and fed into the electrical supply grid 244 via the grid transformer 242, which may be formed as a variable transformer.

[0086] In normal operation, electrical power is consequently generated from wind by the rotor 206 and the generator 220. Part of this power is used for auxiliary devices, such as the indicated pitch drives 222 and the exciter generator 230. However, further and/or other auxiliary devices also come into consideration, such as for example an azimuth adjusting device (drive), with which the rotor 206 can be aligned with the wind. Usually, for this purpose the entire nacelle, such as the nacelle 104 of the wind turbine 100 of FIG. 1, is turned and aligned with the wind.

[0087] The remaining power, which is usually the greater proportion by far of the power generated, is then fed into the electrical supply grid 244.

[0088] Substantially, a voltage level of a link voltage of the second DC link is controlled by the inverter 238 inverting a correspondingly great or small amount of power thereof and ultimately feeding it into the electrical supply grid 244. This may particularly also take place voltage-dependently, to be specific dependent on the link voltage of the second DC link, so that the inverter 238 then substantially controls the link voltage of the second DC link.

[0089] It may also happen that the link voltage of the second DC link 234 nevertheless reaches too high a value, and then a chopper circuit 246, which is likewise arranged in the second DC link 234, will remove power by generating corresponding current pulses, to be specific in such a way that these current pulses lead to a current that is removed by a chopper resistor 248, to be specific in that the power removed is converted into heat in the chopper resistor 248.

[0090] If faulty operation then occurs, in which no power can be fed into the electrical supply grid 244, which is indicated by the opened grid switch 250, the power generated by the generator 220 is reduced, to be specific to a cut-back power that corresponds in its level to an upper auxiliary power limit. This upper auxiliary power limit indicates the power that is required as a maximum by all of the auxiliary devices of the wind turbine together, at least is required as a maximum in the operating situation at the time. For this purpose, in particular the rotor blades 208 may be turned out of the wind by their pitch drives 222 to such an extent that only this cut-back power is generated.

[0091] However, the auxiliary devices do not consume the entire auxiliary power that is provided according to the upper auxiliary power limit the whole time or possibly even at all, or almost at all. Particularly, strong fluctuations in power must be expected due to the switching on and off of auxiliary devices. This applies particularly to the pitch drives 222, but also to the azimuth drives that are mentioned above but are not shown in FIG. 2.

[0092] To allow for such a fluctuating power requirement, sometimes fluctuating suddenly, a store is not used, but instead excess power is in each case removed from the second DC link 234 by the chopper circuit 246.

[0093] FIG. 3 schematically shows possible power variation curves to illustrate the proposed power management. FIG. 3 shows here three diagrams represented one above the other, which use the same time axis. In the upper diagram A, the upper auxiliary power limit P.sub.0 is represented by a horizontal dashed line. Shown respectively underneath is the auxiliary power P.sub.A consumed overall by all of the auxiliary devices. For the purposes of illustration, only a few fluctuations or variations of the auxiliary power outputs PA are shown, to be specific illustrating only a few stages. These stages may be caused for example by the switching on or off of the pitch drives and the azimuth drives. For example, at the point in time t.sub.1 the wind direction could have changed to such an extent that the azimuth drives align the wind turbine with the wind and require power for this, so that the auxiliary power P.sub.A increases there, while at the point in time t.sub.2 the azimuth adjustment has ended. To this extent, the auxiliary power P.sub.A shows consumed power.

[0094] Also depicted in diagram A is the generator power P.sub.G generated, and the diagram to this extent begins with normal operation, in which the generator generates power and feeds it into the electrical power grid after drawing off the auxiliary power P.sub.A. Correspondingly shown is a characteristic curve of the generator power P.sub.G, which may also fluctuate.

[0095] At the point in time t.sub.3, a grid fault occurs, immediately ruling out any feeding of electrical power into the electrical supply grid. Particularly, the grid disconnecting switch 250 shown in FIG. 2 could then be opened. At this point in time, the generator power P.sub.G is then reduced to a cut-back power P.sub.R, which in the example shown corresponds to the upper auxiliary power limit P.sub.0. In other embodiments or other situations, the cut-back power P.sub.R may however also be greater than the upper auxiliary power limit P.sub.0.

[0096] For reducing the generator power, the blades are turned out of the wind, at least partly, so that the pitch drives are activated. Correspondingly, the auxiliary power P.sub.A therefore represents the consumed auxiliary power at the point in time t.sub.3. At the point in time t.sub.4, the blade adjustment by means of the pitch drives has then achieved its aim and it has been possible to reduce the generator power to the desired value of the cut-back power P.sub.R. The pitch drives could then be switched off again, so that the consumed auxiliary power P.sub.A also falls again.

[0097] As from the point in time t.sub.3, there is consequently a grid fault, but the wind turbine continues to be operated substantially normally, apart from the fact that the generator power P.sub.G has been reduced to the cut-back power P.sub.R. Even in this cut-back operating mode, it may happen that the wind turbine must be aligned again in its azimuthal alignment. This is for example indicated at the point in time t.sub.8 by way of example. With varying wind, it may likewise happen that a pitch adjustment becomes necessary, and that is illustrated by way of example at the point in time t.sub.6. At the point in time t.sub.6, the azimuth adjustment is still in operation, so that the two power requirements add together and in this example even reach the upper auxiliary power limit P.sub.0. At the point in time t.sub.7, the azimuth adjustment has then ended, though the pitch adjustment still has not, but then at the point in time t.sub.8 has ended.

[0098] At the point in time t.sub.8, the entire auxiliary power P.sub.A consumed has consequently assumed a comparatively very small value. However, power outputs continue to be required, particularly for an exciter generator, such as the exciter generator 230 of FIG. 2. At this stage it is also pointed out that the power amplitudes shown do not have to be characteristic in terms of the value. Particularly, usually the auxiliary component, that is to say the entire auxiliary power P.sub.A, is a much smaller proportion of the generator power P.sub.G in normal operation, that is to say before the point in time t.sub.3.

[0099] At the point in time t.sub.9, it is then assumed that the grid fault has ended and the rotor blades are then turned again into the wind, in order to generate as much power as possible. This has then ended at the point in time t.sub.10 and the generator power P.sub.G has assumed a normal value again, which does not have to correspond to the value before the grid fault.

[0100] In addition to the characteristic power curve given by way of example in diagram A, the power P.sub.C consumed by the chopper circuit at the corresponding times is illustrated in diagram B. In normal operation, that is to say up until the point in time t.sub.3, no power needs to be consumed, that is to say chopped away. At the beginning of the grid fault at the point in time t.sub.3, however, all excess power of the generator must be immediately chopped away, since in the case explained even the grid switch 250 has been opened in FIG. 2. The chopper power P.sub.C consequently suddenly increases at the point in time t.sub.3 to a high value, to be specific the difference between the generator power P.sub.G and the auxiliary power P.sub.A. With the falling of the generator power P.sub.G, the chopper power P.sub.C also falls correspondingly. However, it does not fall to zero, because more power than the auxiliary devices consume is always still generated. The generator power P.sub.G is therefore greater than the auxiliary power P.sub.A consumed overall.

[0101] At the point in time t.sub.4, the chopper power P.sub.C has reached a comparatively low value, but immediately jumps up again because the pitch drives are switched off, and consequently suddenly less auxiliary power P.sub.A is consumed. At the point in time t.sub.5, the auxiliary power P.sub.A increases to some extent as a result of the azimuth adjustment, so that the chopper power P.sub.C falls correspondingly. At the point in time t.sub.6, the auxiliary power P.sub.A even reaches the upper auxiliary power limit P.sub.0, so that the chopper power P.sub.C falls to zero, but only until the point in time t.sub.7. It then increases again, and at the point in time t.sub.8 increases yet again.

[0102] At the point in time t.sub.9, the grid fault has then ended, and consequently the chopper power P.sub.C falls because the power is then fed into the electrical supply grid. This is also shown in an illustrative manner. In one case, it also comes into consideration here that, to achieve a stable situation in the grid after the grid fault, the entire power that can be generated is not fed in immediately, but instead for example the power increases slowly. Correspondingly, either the rotor blades may be adjusted more slowly and/or else the chopper circuit may be used for raising the fed-in power and part of the power chopped away.

[0103] Diagram C explains the characteristic curve of the fed-in power P.sub.F. At the beginning, the generator power P.sub.G less the auxiliary power P.sub.A is fed in. At the point in time t.sub.1, a little more auxiliary power P.sub.A is used, because of the azimuth adjustment described, and this is taken from the fed-in power P.sub.F, which is consequently correspondingly reduced there. At the point in time t.sub.2, it increases again however, up until the point in time t.sub.3. At the point in time t.sub.3, a grid fault occurs and the fed-in power immediately falls to zero.

[0104] Only at the point in time t.sub.9 does the fed-in power increase again. At this point in time, it can increase suddenly, by the value of the chopper power less the power then required for the pitch drives. At point in time t.sub.2, the power for the pitch drives is then also no longer applicable and the fed-in power P.sub.F can be correspondingly increased.

[0105] It is consequently evident that the auxiliary drives always receive sufficient power, even in the event of a grid fault, without a store being required. The control can be carried out as before, in particular the activation of the chopper circuit can also be used as before. By not taking away the power of the DC link, to be specific for example in the DC link 234 of FIG. 2, the link voltage of the second DC link can increase to such an extent that the chopper circuit is triggered and the power not taken is consumed. In addition, here too the response voltage of the chopper circuit may be lowered.