Method for operating a wind turbine

Abstract

A method for operating a wind power installation which is connected to a network connection point of an electrical supply network and is intended to produce and feed electrical energy into the electrical supply network, wherein the electrical supply network has a network nominal frequency and is operated at a network frequency, and the wind power installation which comprises an electrical generator with a generator nominal power can be regulated on the basis of the network frequency, comprising the steps of: using the electrical generator to produce an electrical generator power for feeding into the electrical supply network, feeding the electrical generator power or a part of it into the electrical supply network as electrical feed-in power on the basis of the network frequency, wherein, in a first supporting stage, the electrical generator power is reduced on the basis of the network frequency in order to accordingly reduce the electrical feed-in power, and, in a second supporting stage, the electrical feed-in power is reduced such that the electrical feed-in power is less than the electrical generator power.

Claims

1. A method for operating a wind power installation that is connected to a network connection point of an electrical supply network, wherein the wind power installation is configured to produce and provide electrical energy into the electrical supply network, wherein the electrical supply network has a network nominal frequency and is operated at a network frequency, and wherein the wind power installation comprises an electrical generator with a generator nominal power, wherein the electrical generator is configured to be regulated based on the network frequency, the method comprising: using the electrical generator to produce an electrical generator power for providing into the electrical supply network; converting the electrical generator power into a first portion; and providing at least the first portion of the electrical generator power into the electrical supply network as electrical feed-in power based on the network frequency, wherein: in a first supporting stage, the method comprises: receiving, from a controller, a fed back signal representative of the network frequency, wherein the electrical generator power is reduced based on the network frequency to reduce the electrical feed-in power, and in a second supporting stage, the method comprises: drawing power from the electrical feed-in power to reduce the electrical feed-in power such that the electrical feed-in power is less than the electrical generator power, wherein the second supporting stage is implemented after the first supporting stage has been completed.

2. The method as claimed in claim 1, wherein in the second supporting stage, the electrical feed-in power is reduced if the network frequency changes with a frequency gradient which exceeds a predetermined limiting gradient.

3. The method as claimed in claim 1, wherein in the second supporting stage, the electrical feed-in power is reduced if the network frequency is above a predetermined frequency value.

4. The method as claimed in claim 1, wherein in the second supporting stage, the electrical feed-in power is reduced if the electrical feed-in power is above a particular power for a predetermined period or exceeds a predetermined power value.

5. The method as claimed in claim 1, wherein in the second supporting stage, the electrical feed-in power is reduced if the second supporting stage is requested by an operator.

6. The method as claimed in claim 1, wherein the second supporting stage is implemented independently of the first supporting stage.

7. The method as claimed in claim 1, wherein the electrical generator power is produced using the electrical generator based on a deviation of the network frequency from the network nominal frequency, wherein the electrical generator power is reduced if the network frequency is above a predetermined desired frequency.

8. The method as claimed in claim 1, wherein the electrical feed-in power is reduced such that the electrical feed-in power is equal to zero.

9. The method as claimed in claim 1, further comprising: removing electrical power from the electrical supply network if the network frequency changes with a frequency gradient that exceeds a predetermined limiting gradient and/or the network frequency is above a predetermined frequency value.

10. The method as claimed in claim 9, wherein the predetermined limiting gradient is at least one of: 0.5 Hz per second; between 0.5 Hz per second and 2 Hz per second; and 2 Hz per second.

11. The method as claimed in claim 1, wherein the electrical feed-in power is reduced in the second supporting stage such that the electrical feed-in power is equal to the electrical generator power if the network frequency changes with a frequency gradient which undershoots a predetermined limiting gradient.

12. The method as claimed in claim 1, wherein the reduction of the electrical feed-in power in the second supporting stage comprises consuming electrical power chosen from at least one of the electrical generator power and electrical power from the electrical supply network, wherein the consuming comprises using a switching device for converting the electrical power into thermal power.

13. The method as claimed in claim 12, wherein the switching device for converting electrical power into the thermal power is configured to convert electrical power corresponding to the generator nominal power into the thermal power for at least three seconds.

14. The method as claimed in claim 12, wherein the switching device for converting electrical power into the thermal power is configured to convert electrical power corresponding to twice the generator nominal power into the thermal power for at least three seconds.

15. The method as claimed in claim 12, wherein the switching device comprises at least one chopper.

16. The method as claimed in claim 12, wherein the switching device is a chopper bank.

17. The method as claimed in claim 1 comprising: converting electrical power that is removed from the electrical supply network to support the network frequency of the electrical supply network if the network frequency changes with a frequency gradient which exceeds a predetermined limit value.

18. A wind power installation, comprising: an electrical generator with a generator nominal power for producing electrical generator power, wherein the wind power installation is configured to convert the electrical generator power into a first portion, and the wind power installation is configured to be connected to a network connection point of an electrical supply network to provide the first at least the portion of the electrical generator power into the electrical supply network as an electrical feed-in power based on a network frequency of the electrical supply network; a rectifier coupled to an output of the electrical generator; a direct current (DC) intermediate circuit coupled to an output of the rectifier; an inverter coupled to an output of the DC intermediate circuit; and a switching device, coupled to the DC intermediate circuit and an output of the inverter, configured to: in a first supporting stage, receive, from a controller, a fed back signal representative of the network frequency, and reduce the electrical generator power based on the network frequency to reduce the electrical feed-in power, and in a second supporting stage, draw power from the electrical feed-in power to reduce the electrical feed-in power such that the electrical feed-in power is less than the electrical generator power, wherein the second supporting stage is implemented after the first supporting stage has been completed.

19. The wind power installation as claimed in claim 18, wherein the switching device is configured to convert the electrical feed-in power into thermal power, wherein the switching device is configured to consume at least part of the electrical generator power to reduce the electrical feed-in power.

20. The wind power installation as claimed in claim 19, wherein the switching device is configured to convert electrical power corresponding to the generator nominal power into the thermal power for at least three seconds.

21. The wind power installation as claimed in claim 19, wherein the switching device is a chopper bank and comprises a rectifier.

22. A wind farm comprising: a plurality of wind power installations, wherein at least one wind power installation of the plurality of wind power installations is the wind power installation as claimed in claim 18, and a wind farm controller configured to transmit control signals to the plurality of wind power installations and to receive status signals provided by the plurality of wind power installations to determine a negative electrical wind farm power or energy.

23. The wind farm as claimed in claim 22, wherein the wind farm controller is configured to: request status signals from the at least one wind power installation, wherein the status signals are indicative of a readiness of switching devices of the at least one wind power installation to consume power or energy; determine the negative electrical wind farm power or energy based on the requested status signals; and provide a supply network operator and/or a control room controlling the wind farm with the determined negative electrical wind farm power or energy.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The determined negative powers or energies of the individual wind power installations which are provided by the switching devices of the wind power installations are added up to form a negative electrical wind farm power or energy and are made available to the supply network operator, for example, as information. The supply network operator can then retrieve this negative wind farm power or energy provided in this manner if necessary in order to support the electrical supply network. The present invention is now explained in more detail below by way of example on the basis of exemplary embodiments with reference to the accompanying figures.

(2) FIG. 1 shows a schematic view of a preferred wind power installation.

(3) FIG. 2 shows a schematic structure of an electrical section of a wind power installation for producing and feeding in electrical energy according to one embodiment.

(4) FIG. 3 schematically shows a sequence of the method for operating a wind power installation in one preferred embodiment.

(5) FIG. 4 schematically shows an overfrequency power consumption with a wind power installation according to one embodiment.

(6) FIG. 5 shows a schematic structure of a wind farm for producing and feeding in electrical energy according to one embodiment.

DETAILED DESCRIPTION

(7) FIG. 1 shows a wind power installation 100 for producing and feeding electrical energy into an electrical supply network.

(8) For this purpose, the wind power installation 100 has a tower 102 and a nacelle 104. An aerodynamic rotor 106 having three rotor blades 108 and a spinner 110 is arranged on the nacelle 104. During operation, the rotor 106 is caused to rotate by the wind and thereby drives an electrical generator in the nacelle 104, wherein the generator is preferably in the form of a six-phase ring generator.

(9) FIG. 2 shows, in a simplified manner, an electrical section 200 of a wind power installation shown in FIG. 1.

(10) The electrical section 200 has a six-phase ring generator 210 with a generator nominal power for producing an electrical generator power P.sub.GEN, which generator is caused to rotate by the wind via a mechanical drive train of the wind power installation in order to produce a six-phase electrical alternating current. The six-phase electrical alternating current is transferred, by the electrical generator 210, to the rectifier 220 which is connected to the three-phase inverter 240 via a DC voltage intermediate circuit 230. The six-phase ring generator 210 which is in the form of a synchronous generator is controlled in this case via excitation 250 from the DC voltage intermediate circuit 230, wherein the excitation can also be supplied from another source, in particular by means of a separate current controller.

(11) The electrical section 200 therefore has a full converter concept in which the electrical feed-in power P.sub.EIN is fed into the network 270 by means of the three-phase inverter 240 via the wind power installation transformer 260. This network 270 is usually a wind farm network which feeds an electrical supply network via a wind farm transformer.

(12) In order to produce the three-phase current I.sub.1, I.sub.2, I.sub.3 for each of the phases U, V, W, the inverter 240 is controlled with a tolerance band method. In this case, the control is effected via the controller 242 which captures each of the three currents I.sub.1, I.sub.2, I.sub.3 produced by the inverter 240 by means of a current capture unit 244. The controller 242 is therefore set up to individually control each phase of the inverter 240 by means of the current capture unit 244. For this purpose, a desired current value I.sub.SOLL can be specified to the controller 242, on the basis of which the currents I.sub.1, I.sub.2, I.sub.3 are adjusted. The desired current value I.sub.SOLL is preferably individually calculated for each phase U, V, W inside the installation and is specified for the controller 242.

(13) The electrical section 200 also has a switching device 280 for converting electrical power into thermal power, which switching device is set up to convert electrical power corresponding to twice the generator nominal power into thermal power ΔP.sub.TH for at least five seconds.

(14) The switching device 280 can be connected either (A) to the DC voltage intermediate circuit 230 or (B) to the phases U, V, W between the inverter 240 and the wind power installation transformer 260 via a diode rectifier 282 in order to reduce the electrical feed-in power P.sub.EIN such that the electrical feed-in power P.sub.EIN is less than the electrical generator power P.sub.GEN if the network frequency changes with a frequency gradient which exceeds a predetermined limit value. The switching device 280 is therefore set up to convert large powers.

(15) In order to reduce the electrical feed-in power P.sub.EIN, the switching device 280 has a control input 284 for receiving control signals S from the wind power installation controller or from the wind farm controller and for transferring or returning further signals to the controllers.

(16) If, for example, the network frequency changes with a frequency gradient which exceeds a predetermined limit value, the switching device 280 is activated in order to reduce the feed-in power P.sub.EIN. The electrical generator power P.sub.GEN produced by the generator 210 is therefore reduced by means of the switching device 280 in such a manner that the feed-in power P.sub.EIN is reduced. The switching device 280 is therefore an apparatus for converting high electrical powers into thermal power. For this purpose, the switching device is preferably in the form of a chopper bank for converting large powers and energies. The switching device 280 is also controlled on the basis of the network frequency, in particular on the basis of a frequency gradient.

(17) FIG. 3 schematically shows a sequence 300 of the method for operating a wind power installation in one preferred embodiment. The method relates, in particular, to the reduction of the electrical feed-in power in such a manner that the electrical feed-in power is less than the electrical generator power if the network frequency changes with a frequency gradient which exceeds a predetermined limit value.

(18) For this purpose, the generator of the wind power installation produces an electrical generator power for feeding into the electrical supply network while the supply network is in a stable state. This means, in particular, that the network frequency f.sub.N corresponds substantially to the network nominal frequency f.sub.NENN and the frequency gradient of the network frequency df.sub.N/dt is less than the predetermined limit value G. Block 310 indicates that the frequency gradient of the network frequency df.sub.N/dt is less than the predetermined limit value G of the frequency gradient and block 340 indicates that the network frequency f.sub.N corresponds substantially to the network nominal frequency f.sub.NENN.

(19) If the frequency gradient of the network frequency df.sub.N/dt is less than the predetermined limit value G, the switching device for converting electrical power into thermal power does not convert any thermal power ΔP.sub.TH. This is indicated by block 320.

(20) The check in order to determine whether the frequency gradient of the network frequency df.sub.N/dt is less than the predetermined limit value G is dynamically carried out, for example by capturing the network frequency f.sub.N and subsequently averaging the dynamically captured network frequency f.sub.N over time t. Block 325 indicates the dynamic capture of the frequency gradient of the network frequency df.sub.N/dt.

(21) If the frequency gradient of the network frequency df.sub.N/dt is less than the predetermined limit value G, the switching device still does not convert any thermal power P.sub.TH.

(22) However, if the frequency gradient of the network frequency df.sub.N/dt exceeds the predetermined limit value G, the switching device converts electrical power, in particular part of the electrical generator power P.sub.GEN, into thermal power P.sub.TH. This directly reduces the electrical feed-in power P.sub.EIN. Block 330 indicates that the electrical feed-in power P.sub.EIN is directly reduced by converting electrical power into thermal power ΔP.sub.TH.

(23) If the frequency gradient of the network frequency df.sub.N/dt is then less than the predetermined limit value G again, the switching device stops the conversion of the electrical power.

(24) If the frequency gradient of the network frequency df.sub.N/dt still exceeds the predetermined limit value G, electrical power continues to be converted and the absolute value of the converted electrical power is increased further.

(25) In order to prevent overloading of the switching device, the temperature of the switching device is preferably monitored. This is indicated by block 335.

(26) If the converted thermal energy ΔE.sub.TH exceeds a critical limit value E.sub.KRIT, the electrical generator power P.sub.GEN is additionally reduced or the electrical generator is powered down such that the wind power installation no longer feeds in any electrical power. This is indicated by block 390.

(27) The method can therefore be carried out independently of the generator control which regulates a generator on the basis of the network frequency.

(28) The generator regulation is preferably operated independently of the control of the switching device.

(29) If the network frequency f.sub.N is substantially less than or equal to the network nominal frequency f.sub.NENN, the generator preferably feeds the entire electrical generator power P.sub.GEN produced into the electrical supply network as electrical feed-in power P.sub.EIN. This is indicated by block 350.

(30) The check in order to determine whether the network frequency f.sub.N is less than or equal to the network nominal frequency f.sub.NENN or is less than or equal to a predetermined desired frequency f.sub.SOLL is indicated by block 355. For example, if the network nominal frequency is 50 Hz and the desired frequency is 50.1 Hz, the generator then has a type of dead band in its regulation. The network frequency f.sub.N can also be captured by a wind farm control unit which determines, by means of a comparison, whether the network frequency f.sub.N exceeds the network nominal frequency f.sub.NENN or the desired frequency f.sub.SOLL.

(31) If the network frequency f.sub.N is substantially less than or equal to the network nominal frequency f.sub.NENN or the desired frequency f.sub.SOLL, the generator still feeds the entire electrical generator power P.sub.GEN produced into the electrical supply network as electrical feed-in power P.sub.EIN.

(32) However, if the network frequency f.sub.N exceeds the network nominal frequency f.sub.NENN or the desired frequency f.sub.SOLL, the electrical generator power P.sub.GEN is reduced. The generator then feeds a reduced electrical generator power P.sub.GEN into the electrical supply network as electrical feed-in power P.sub.EIN. Block 360 indicates the fact that the generator feeds a reduced electrical generator power into the electrical supply network as electrical feed-in power P.sub.EIN on the basis of the network frequency f.sub.N if a desired frequency f.sub.SOLL is exceeded.

(33) If the network frequency f.sub.N now undershoots or corresponds to the network nominal frequency f.sub.NENN or the desired frequency f.sub.SOLL again, the electrical generator retains its state and is started up again.

(34) If the network frequency f.sub.N still exceeds the network nominal frequency f.sub.NENN or the desired frequency f.sub.SOLL, the electrical generator power P.sub.GEN is again or still reduced.

(35) If the network frequency f.sub.N nevertheless exceeds a critical frequency f.sub.KRIT specified by the network operator, for example, the electrical generator power P.sub.GEN is considerably reduced or the generator is changed to a state in which it no longer produces any electrical generator power. Block 390 indicates the fact that the electrical generator is powered down such that the wind power installation no longer feeds in any electrical power.

(36) FIG. 4 schematically shows an overfrequency power consumption 400 with a wind power installation according to one embodiment. In this case, in particular, the method of operation of the method is shown on the basis of a fluctuation in the network frequency f.sub.N.

(37) The network frequency f.sub.N is plotted against the time tin the upper graph 410. In this case, the network frequency is a few hundredths more than the network nominal frequency f.sub.NENN of 50 Hz, for example 50.02 Hz, and fluctuates slightly. Until the time t1, the electrical supply network therefore behaves in a substantially frequency-stable manner, that is to say it does not have any major frequency deviation or a relatively steep frequency gradient.

(38) The electrical generator power P.sub.GEN is plotted against the time in the central graph 420. In this case, the generator is controlled on the basis of the network frequency f.sub.N and produces the slightly oscillating generator power P.sub.GEN. The thermal power ΔP.sub.TH converted by the switching device is likewise depicted in the central graph 420. In this case, the switching device is controlled on the basis of the frequency gradient df.sub.N/dt. Since the electrical supply network does not have a frequency gradient df.sub.N/dt which exceeds the predetermined limit value G, no electrical power, in particular electrical generator power, is converted into thermal power.

(39) The electrical feed-in power P.sub.EN results from the electrical generator power P.sub.GEN and the thermally converted power and, until the time t1, corresponds substantially to the electrical generator power P.sub.GEN. This is shown in the lower graph 430.

(40) At the time t1, the electrical supply network has a disruption in the form of a frequency gradient 412 which is greater than the predetermined limit value G. This can be captured by means of a measuring device, for example.

(41) The switching device, in particular the power chopper, is then activated. This is shown in the lower half-plane 422 of the central graph. The electrical generator which is controlled on the basis of a frequency deviation remains unaffected by this, at least for the time being.

(42) The switching-on of the switching device results in both the entire electrical generator power P.sub.GEN and a part of the electrical power removed from the electrical supply network, in order to stabilize the electrical supply network, being converted into thermal power, in particular heat. This is illustrated in the graph 430. The switching device therefore not only reduces the electrical feed-in power to 0 by converting the electrical generator power into thermal power but also converts additional excess power, in particular active power, from the electrical supply network into thermal power. The wind power installation therefore has a negative power, in particular a negative active power balance, at the connection point.

(43) On account of this measure, the network frequency slowly recovers again, with the result that the network frequency with a frequency gradient 414 approaches the network nominal frequency, wherein the frequency gradient 414 is less than the predetermined limit value.

(44) The switching device hereupon slowly reduces its power consumption of the electrical generator power until the supply network again has a frequency-stable state at the time t2.

(45) During the performance of the method, the electrical generator power is preferably also reduced on the basis of the network frequency, in particular if a frequency deviation is more than 0.2 Hz from the network nominal frequency and lasts for more than five seconds. This is illustrated, by way of example, in the central graph 420 in the region 424.

(46) FIG. 5 shows a wind farm 500 having, by way of example, three wind power installations 100 according to FIG. 1. The three wind power installations are therefore representative of fundamentally any desired number of wind power installations in a wind farm 500. The wind power installations 100 provide their electrical feed-in power P.sub.EN via an electrical wind farm network 570. These individual feed-in powers P.sub.EN are fed into the supply network 594 together as a wind farm power P.sub.PARK at a network connection point PCC via the wind farm transformer 590 which steps up the voltage in the farm.

(47) In this case, the wind farm 500 is controlled via a wind farm control unit 542 which is also referred to as a farm control unit FCU. For this purpose, the wind farm control unit 542 captures the network frequency and, in particular, the frequency deviation and the frequency gradient by means of measuring means 544. The wind farm control unit can also communicate with the individual wind power installations via the control lines 546. In particular, status signals S from the wind power installation, for example the energy consumption readiness of the switching devices, can be requested thereby. On the basis of these requested status signals S, the wind farm control unit 542 can calculate a negative electrical wind farm energy, that is to say the energy which the wind farm is ready to consume. This negative wind farm energy calculated in this manner is then made available to a supply network operator by means of reduction signal R. The supply network operator is therefore always informed of how much electrical power, in particular active power, the wind farm can consume and can in turn also request this. The wind farm is therefore set up to act as a consumer of active power for at least five seconds, in particular with a negative power corresponding to the wind farm nominal power.