OPERATION OF A WIND TURBINE DURING START-UP TO REDUCE LIMIT CYCLES

Abstract

The invention relates to a method for controlling a wind turbine during start up, from a non-producing operation mode to a power producing operation mode when limit cycles occur during start-up. Limit cycles are detected when a number of cut-in transitions or a number of cut-out transitions are detected. A cut-in transition is when the wind turbine fails starting up despite having the wind speed or rotor speed normally required to enter a power producing operation mode. A cut-out transition is occurring when the wind turbine is falling out of power producing operation mode after having entered the power producing operation mode.

Claims

1. A method for operating a wind turbine during start-up from a non-producing operation mode to a power producing operation mode, the method comprising: a) setting a nominal cut-in value of a first operational parameter and a connection cut-in value of a second operational parameter of the wind turbine; b) monitoring the first operational parameter; c) initiating start-up of the wind turbine when the monitored first operational parameter is higher than the nominal cut-in value; d) monitoring the second operational parameter; e) detecting a cut-in transition if the value of the second operational parameter is not reaching the connection cut-in value within a start-up time period or the first operational parameter falls below the nominal cut-in value; f) detecting a cut-in limit cycle of the wind turbine if more than a threshold number of counted cut-in transitions has been detected, and if a cut-in limit cycle is detected, increase the nominal cut-in value; and g) repeating steps b)-f) until the second operational parameter reaches the connection cut-in value.

2. The method of claim 1, wherein the method further comprises: h) entering a power producing operation mode of the wind turbine upon reaching the connection cut-in value of the second operational parameter; i) monitoring the operational state of the wind turbine; j) detecting a cut-out transition upon transition into a non-producing operation mode or within a connection time period after transition into a non-producing operation mode not reaching a power producing operation mode; k) detecting a connection limit cycle of the wind turbine if more than a threshold number of counted cut-out transitions has been detected, and if a connection limit cycle is detected, increase the connection cut-in value; l) repeating step b)-f) after detecting a cut-out transition until the second operational value reaches the connection cut-in value; m) entering a power producing operation mode of the wind turbine; and n) repeating steps i)-l) until no cut-out transition has been detected within a timeout-period after which the wind turbine enters normal operation.

3. The method of claim 2, wherein the method further comprises resetting the nominal cut-in value to its initial value upon detecting a connection limit cycle and the connection cut-in value is lower than a connection threshold.

4. The method of claim 3, wherein the method further comprises increasing the nominal cut-in value upon detecting a connection limit cycle and the connection cut-in value is higher than or equal to the connection threshold.

5. The method of claim 1, wherein the method further comprises setting the nominal cut-in value to a nominal threshold upon detecting a cut-in limit cycle of the wind turbine and the nominal cut-in value is higher than or equal to the nominal threshold.

6. The method of claim 2, wherein the method further comprises setting the connection cut-in value to a connection threshold upon detecting a connection limit cycle of the wind turbine and the connection cut-in value is higher than or equal to the connection threshold.

7. The method of claim 1, wherein the method further comprises resetting the nominal cut-in value and the connection cut-in value to their initial values when no cut-out transition has been detected within the timeout-period after which the wind turbine enters normal operation.

8. The method of claim 1, wherein the counted cut-in transitions is reset to zero when a cut-in limit cycle is detected or a cut-in limit cycle timer times out.

9. The method of claim 1, wherein the counted cut-out transitions is reset to zero when a connection limit cycle is detected or a connection limit cycle timer times out.

10. The method of claim 1, wherein the first operational parameter is the wind speed or the rotor speed, and the second operational parameter is the rotor speed.

11. The method of claim 1, wherein when the first operational parameter is the wind speed and the nominal cut-in value is initially set to 3, 4 or 5 m/s and when the first operational parameter is increased, it is increased with 1 m/s steps.

12. The method of claim 1, wherein when the second operational parameter is the rotor speed, the connection cut in value is initially set to 0.5, 1, or 1.2 rpm and when the second operational parameter is increased, it is increased with 2.5% steps.

13. The method of claim 1, wherein the threshold number of cut-out transitions is 2, 3, 4, 5, 6 or 7.

14. The method of claim 1, wherein the timeout-period after which the wind turbine enters normal operation is 2, 3, 4, 5 or 6 hours.

15. A method for operating a wind turbine during start-up from a non-producing operation mode to a power producing operation mode, the method comprising:

0. setting a connection cut-in value of a second operational parameter of the wind turbine; p) monitoring the second operational parameter; q) entering a power producing operation mode of the wind turbine upon reaching the connection cut-in value of the second operational parameter; r) monitoring the operational state of the wind turbine; s) detecting a cut-out transition upon transition into a non-producing operation mode or within a connection time period after transition into a non-producing operation mode not reaching a power producing operation mode; t) detecting a connection limit cycle of the wind turbine if more than a threshold number of counted cut-out transitions has been detected, and if a connection limit cycle is detected, increase the connection cut-in value; and u) repeating steps p)-t) until no cut-out transition has been detected within a timeout-period after which the wind turbine enters normal operation.

16. A control system, comprising: an input/out interface; and one or more processors configured to permorm an operation for operating a wind turbine system during start-up, the operation, comprising: a) setting a nominal cut-in value of a first operational parameter and a connection cut-in value of a second operational parameter of the wind turbine; b) monitoring the first operational parameter; c) initiating start-up of the wind turbine when the monitored first operational parameter is higher than the nominal cut-in value; d) monitoring the second operational parameter; e) detecting a cut-in transition if the value of the second operational parameter is not reaching the connection cut-in value within a start-up time period or the first operational parameter falls below the nominal cut-in value; f) detecting a cut-in limit cycle of the wind turbine if more than a threshold number of counted cut-in transitions has been detected, and if a cut-in limit cycle is detected, increase the nominal cut-in value; and g) repeating steps b)-f) until the second operational parameter reaches the connection cut-in value.

17. A wind turbine system, comprising: a tower; a nacelle disposed on the tower; a rotor extending from the nacelle and having a plurality of blades disposed at a distal end of the rotor; and a control system for operating a wind turbine system during start-up, the control system configured to perform an operation, comprising: a) setting a nominal cut-in value of a first operational parameter and a connection cut-in value of a second operational parameter of the wind turbine; b) monitoring the first operational parameter; c) initiating start-up of the wind turbine when the monitored first operational parameter is higher than the nominal cut-in value; d) monitoring the second operational parameter; e) detecting a cut-in transition if the value of the second operational parameter is not reaching the connection cut-in value within a start-up time period or the first operational parameter falls below the nominal cut-in value; f) detecting a cut-in limit cycle of the wind turbine if more than a threshold number of counted cut-in transitions has been detected, and if a cut-in limit cycle is detected, increase the nominal cut-in value; and g) repeating steps b)-f) until the second operational parameter reaches the connection cut-in value.

18. A computer program product comprising software code adapted to control a wind turbine system when executed on a data processing system, the computer program product being adapted to perform an operation, comprising: a) setting a nominal cut-in value of a first operational parameter and a connection cut-in value of a second operational parameter of the wind turbine; b) monitoring the first operational parameter; c) initiating start-up of the wind turbine when the monitored first operational parameter is higher than the nominal cut-in value; d) monitoring the second operational parameter; e) detecting a cut-in transition if the value of the second operational parameter is not reaching the connection cut-in value within a start-up time period or the first operational parameter falls below the nominal cut-in value; f) detecting a cut-in limit cycle of the wind turbine if more than a threshold number of counted cut-in transitions has been detected, and if a cut-in limit cycle is detected, increase the nominal cut-in value; and g) repeating steps b)-f) until the second operational parameter reaches the connection cut-in value.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0082] The wind turbine according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0083] FIG. 1 illustrates a wind turbine,

[0084] FIG. 2 is a flow chart illustrating the start-up of the wind turbine into a power producing operation mode,

[0085] FIG. 3 is a flow chart illustrating the method after entering power producing operation mode,

[0086] FIG. 4 illustrates the operation of the wind turbine,

[0087] FIG. 5 illustrates a cut-in limit cycle state machine for controlling the cut-in limit cycle,

[0088] FIG. 6 illustrates a connection limit cycle state machine for controlling the connection limit cycle,

[0089] FIG. 7 illustrates controlling the wind turbine only by the connection limit cycles according to the second aspect of the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

[0090] FIG. 1 shows a wind turbine 100 (also commonly referred to as a wind turbine generator, WTG) comprising a tower 101 and a rotor 102 with at least one rotor blade 103. Typically, three blades are used, but a different number of blades can also be used. The blades 103 are connected with the hub 105, which is arranged to rotate with the blades. The rotor is connected to a nacelle 104, which is mounted on top of the tower 101 and being adapted to drive a generator situated inside the nacelle 104. The rotor 102 is rotatable by action of the wind. The wind induced rotational energy of the rotor blades 103 is transferred via a shaft to the generator. Thus, the wind turbine 100 is capable of converting kinetic energy of the wind into mechanical energy by means of the rotor blades and, subsequently, into electric power by means of the generator. The generator is connected with a power converter. Moreover, the wind turbine 100 comprises a control system. The control system may be placed inside the nacelle 104, or distributed at a number of locations inside the turbine 100 and communicatively connected.

[0091] FIG. 2 illustrates the start-up of the wind turbine. In the first step 201, the nominal cut-in value of the first operational parameter and the connection cut-in value of the second operation parameter is set to initial values. The first operational parameter typically is the wind speed and the nominal cut-in value for the first operational parameter may for instance be set to 3 m/s. Alternatively, the first operational parameter may be the rotor speed. The second operational parameter typical is rotor speed and the connection cut-in value of the second operational parameter may for instance be set to 0.5 rpm. Further the cut-in counter, used to count cut-in transitions, is set to zero.

[0092] In step 202, the first operational parameter is monitored. The monitoring is typically performed by the wind turbine control system. Then, in 203, when the first operational parameter is higher than the nominal cut in value, for instance when the measured wind speed is higher than 3 m/s, the wind turbine enters step 204 and initiates start-up.

[0093] Then in step 205, the second operational parameter is monitored. The second operational parameter typical may be rotor speed, and it is monitored by the control system by a rotor speed sensor. When, in 206, the second operational parameter is higher than the connection cut-in value, for instance, when the rotor speed is higher than 0.5 rpm, then step 207 is reached, the wind turbine is ready to enter power producing operation mode, and the method continues in FIG. 3.

[0094] However, if the condition, in 206, of the second operational parameter being larger than the connection cut-in value, is not fulfilled after a start-up time period 208, the start-up time period may typically be 180 seconds, a cut-in transition is detected in step 209. When a cut-in transition is detected, the cut-in counter is increased by 1, and if the condition, in 210, is fulfilled, the cut-in counter is higher than the allowed cut-in cycle maximum, then a cut-in limit cycle has been detected 211. When a cut-in limit cycle has been detected 211, the nominal cut-in value is increased, for instance by 1 m/s, and the cut-in counter is reset to zero and the control returns to step 202. The control returns to step 202 whether a cut-in limit cycle has been detected or not. When a cut-in transition has been detected, the control starts over to monitor the first operational parameter for when to make a new attempt to initiate start-up.

[0095] FIG. 3 illustrates the method after the second operational parameter has reached the connection cut-in value and the wind turbine is ready to start up power production. In the first step 301 in FIG. 3, the wind turbine enters a power producing operation mode and starts to produce power for the utility grid. The cut-out counter is set to zero, ready to count cut-out transitions. In step 302, the operational state of the wind turbine is monitored, and if the wind turbine are unable to continue producing power, for instance due to changes in wind speed or wind direction, the wind turbine drops into a non-producing operation mode and a cut-out transition is detected 303. When a cut-out transition is detected, in step 304 the cut-out counter is increased by 1, and if, in 305, the cut-out counter is larger than the allowed connection cycle maximum, a connection limit cycle is detected 306, and the control returns to step 202. In step 306 the connection cut-in value is increased and the cut-out counter is reset to zero. After detecting a cut-out transition, the control returns to step 202 whether a connection limit cycle has been detected or not. When a cut-out transition has been detected, the control starts over monitoring the first operational parameter for when to make a new attempt to initiate start-up. Before returning to step 202 in FIG. 2, the cut-in counter is reset to zero 307.

[0096] If, when monitoring the operational state 302, no cut-out transition has occurred within a time-out period, which for instance may be 2 hours, a timeout occurs and the wind turbine enters normal operation, step 308, and the start-up is completed.

[0097] FIG. 4 illustrates an example operation of the wind turbine. The wind turbine may be in a non-producing operation mode 401 or in a power producing operation mode 402. When in the non-producing operation mode 401, the first operational parameter is monitored 403, when the first operational parameter is becoming larger than the nominal cut-in value; the second operational parameter is monitored 404. When the second operational parameter is higher than the connection cut-in value, the mode of the wind turbine shifts to a power producing operation mode. In the power producing operation mode the operational state of the wind turbine is monitored 405 and if a time-out period expires, the wind turbine shifts to normal operation 406.

[0098] In the non-producing operation mode 401, when monitoring the second operational parameter 404, a cut-in transition 407 may occur and the wind turbine shifts back to monitor the first operational parameter. When in power producing operation mode 402 a cut-out transition 408 may occur and the wind turbine shifts back to non-producing operation mode 401 where it starts with monitoring the first operational parameter 403.

[0099] In embodiments, the method of the invention may be implemented by the use of state machines to monitor the limit cycles. Monitoring the limit cycles by use of state machines is illustrated in FIGS. 5 and 6. FIG. 5 illustrates a cut-in limit cycle state machine 500 for controlling the cut-in limit cycle. The cut-in limit cycle state machine is keeping track of the number of cut-in transitions and detects cut-in limit cycles.

[0100] The state machine is active whenever an event happens that make the cut-in limit cycle state machine change state. In the waiting state 501, the state machine waits for a cut-in transition to happen. Cut-in transitions happens when the wind turbine is attempting to start up because the first operational parameter, typically the wind speed, is higher than the nominal cut-in value, but the wind turbine is unable to reach the second operational parameter, typically the rotor speed, to reach the connection cut-in value before a start-up time period expires. If after the first operational parameter reaches the nominal cut-in value and the second operational parameter is not reaching the connection cut-in value within the start-up time period, a cut-in transition occurs 505. Then the state of the cut-in limit cycle state machine 500 changes to the detecting state 502. In the detecting state 502, the cut-in counter is increased by 1 and the cut-in limit cycle timer is running. Whenever a cut-in transition occurs 506 the detecting state repeats itself. If the cut-in counter becomes larger than the cut-in cycle maximum 507, because there has been more cut-in transitions than allowed according to the setting of the cut-in cycle maximum, the state machine 500 changes state to the cut-in limit cycle detected state 50. In the cut-in limit cycle detected state the nominal cut-in value is increased, and the state machine returns to the waiting state 501. If, when in the detecting state 502, a time-out occurs 508 by the cut-in limit cycle timer timing out, the state machine goes to the timed out state 504, and then to the waiting state 501.

[0101] FIG. 6 illustrates a connection limit cycle state machine 600 for controlling the connection limit cycle. The connection limit cycle state machine is keeping track of the number of cut-out transitions and detects connection limit cycles. The state machine is active whenever an event happens that makes the connection limit cycle state machine change state. In the waiting state 601, the state machine waits for a cut-out transition to happen. Cut-out transitions 605 happens when the wind turbine is producing power in the power producing operation mode, but then are falling out and it no longer producing power. Then the state of the connection limit cycle state machine 600 changes to the detecting state 602. In the detecting state 602, the cut-out counter is increased by 1 and the connection limit cycle timer is running. Whenever a cut-out transition occurs 606 the detecting state repeats itself. If the cut-out counter becomes larger than the connection cycle maximum 607, because there has been more cut-out transitions than allowed according to the setting of the connection cycle maximum, the state machine 600 changes state to the connection limit cycle detected state 603. In the connection limit cycle detected state, the connection cut-in value is increased, and the state machine returns to the waiting state 601. If when in the detecting state 602 a time-out occurs 608 by the connection limit cycle timer timing out, the state machine goes to the timed out state 604 and then to the waiting state 601.

[0102] FIG. 7 illustrates an embodiment where the wind turbine is controlled only by the connection limit cycles according to the second aspect of the invention. In step 701, the second operational parameter is set to the connection cut-in value, and the cut-out counter for counting cut-out transitions is set to zero. Then in step 702 the second operational parameter is monitored. In addition, if, in 703, the second operational parameter becomes larger than the connection cut-in value, then in step 704, the wind turbine is entering the power producing operation mode. When in power production mode the operational state of the wind turbine is monitored in step 705, and if, in 706, a cut-out transition is detected, then, in step 707, one is added to the cut-out counter. If 708 the cut-out counter is larger than the connection cycle maximum, then a connection limit cycle is detected and in step 709 the connection cut-in value is increased and the cut-out counter is reset to zero, prepared to detect another connection limit cycle. Whether a connection limit cycle is detected or not, after detecting a cut-out transition the control returns to step 702 for monitoring the second operational parameter awaiting a new opportunity to enter the power producing operation mode. If the wind turbine is producing power, and after a timeout-period not have detected any cut-out transition, meaning that no fall-out of production has been detected. Then, a timeout occurs, and in step 710, the wind turbine is producing power in a stable manner, and no more special start-up control is needed. Therefore, the connection cut-in value are reset to its initial value and the wind turbine enters normal operation.

[0103] The invention can be implemented by means of hardware, software, firmware or any combination of these. The invention or some of the features there of can also be implemented as software running on one or more data processors and/or digital signal processors.

[0104] The individual elements of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way such as in a single unit, in a plurality of units or as part of separate functional units. The invention may be implemented in a single unit, or be both physically and functionally distributed between different units and processors.

[0105] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is to be interpreted in the light of the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. In addition, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.