High Yaw Error and Gust Ride Through

Abstract

The present invention relates to a system adapted to reduce the load of a wind turbine in situations with high yaw error or by gust ride, which system has access to at least some operational parameters. The object is to reduce the maximal load of a wind turbine in situations where wind gust hits the wind turbine. The system can monitor at least a combination of these parameters, which system by a defined combination of at least some of actual parameters performs a pitch or speed regulation in order to bring the wind turbine into a safe mode of operation and reduce the load of the wind turbine. Hereby can be achieved that the system can monitor some of existing parameters for a wind turbine in operation and through these parameters it is possible with this system to perform an analysis of critical combinations of parameter values. In that way the system can react if a critical load exists because there is a critical combination of parameters and change the pitch of the blades towards the feathered position or by speed reduction.

Claims

1. System (2) adapted to reduce the load of a wind turbine (4) in situations with high yaw error in combination with gust, which system (2) comprising a tower (6) carrying a yaw able nacelle (8), which nacelle (8) carries at least one rotating pitch regulated blade (10), which system (2) has access to at least the following parameters, wind speed (12), yaw error (14), rotor speed (16), pitch angle (18) and power production (20), wherein the system (2) monitors at least a combination of these parameters (12,14,16,18,20), which system by defined combination of at least some of actual parameters (12,14,16,18,20) performs a pitch regulation (22) whereby the average pitch angle (18) is defined by a pitch angle limit vector (26) and a corresponding wind speed vector (28), whereby the yaw angle is defined by a yaw error (14) limit vector and a corresponding wind speed vector (28), in order to bring the wind turbine (4) into a safe mode of operation and reduce the load of the wind turbine (4).

2. System according to claim 1, wherein the safe mode of operating is activated by the following conditions: a. rotor acceleration (24) is higher than a specified parameter value, and b. the average pitch angle (18) for all blades is less than a specified value at the given wind speed (12), and c. the yaw error (14) is higher than a specified value at the given wind speed (12).

3. System according to claim 1, wherein the safe mode of operating is activated by the following conditions: a. the average pitch angle (18) for all blades (10) is smaller than a specified value at the given wind speed (12), and b. the yaw error (14) is higher than a specified value at the given wind speed (12).

4. System according to claim 3, wherein the average pitch angle (18) is defined by a pitch angle limit vector (26) and a corresponding wind speed vector (28).

5. System according to claim 3, wherein the yaw angle is defined by a yaw error (14) limit vector and a corresponding wind speed vector (28).

6. System according to claim 1, wherein when conditions: a. rotor acceleration (24) is higher than a specified parameter value, and b. the average pitch angle (18) for all blades is less than a specified value at the given wind speed (12), and c. the yaw error (14) is higher than a specified value at the given wind speed (12) have not been fulfilled in a specified period, power reference and rotor speed reference are ramped up to normal operation values allowing the wind turbine (4) to operate normally.

7. Method to reduce the load of a wind turbine (4) in situations with high yaw error or by gust as disclosed in claim 1 wherein the following operational parameters are monitored: wind speed (12), yaw error (14), rotor speed (16), pitch angle (18), power production (20), by which method analysis of a defined combination of at least some of the actual parameters (12,14,16,18,20), which method performs a pitch regulation (22) in order to bring the wind turbine (4) into a safe mode of operation and thereby reduce the load of the wind turbine (4).

8. Method according to claim 7, wherein the method compares actual parameters with defined limits for the parameters: a. rotor acceleration (24) is higher than a specified parameter value, and b. the average pitch angle (18) for all blades (10) is less than a specified value at the given wind speed (12), and c. the yaw error (14) is higher than a specified value at the given wind speed (12), which method performs a pitch regulation in order to reduce the load on the wind turbine (4).

9. Method according to claim 7, wherein the method compares actual parameters with defined limits for the parameters: a. the average pitch angle (18) for all blades (10) is less than a specified value at the given wind speed (12), and b. the yaw error (14) is higher than a specified value at the given wind speed (12), which method performs a pitch regulation in order to reduce the load on the wind turbine (4).

Description

DESCRIPTION OF THE DRAWING

[0061] FIG. 1 shows a wind turbine.

[0062] FIG. 2 shows a table of parameters.

DETAILED DESCRIPTION OF THE INVENTION

[0063] FIG. 1 shows a wind turbine 4 and a system 2 in order to control high yaw error and gust ride through of the wind turbine 4. The turbine 4 comprises a tower 6, a nacelle 8 and blades 10. Not shown in the figure is gear and one or more generators placed in the nacelle 8. The system 2 for control of high yaw error and gust ride through comprises a list of parameters. Based on analysis of these actual measured parameters the system is able to perform pitch or speed regulation in order to reduce the load on the tower 6, blades 10 or nacelle 8, if one of the parameters or a combination of the parameters has come into a critical combination. By reducing the power production in critical situations the maximal load on blade, nacelle and tower is limited so the stress of the components is probably reduced. This can lead to higher reliability and a much longer lifetime of the tower and nacelle, maybe also the blades. Further it can be used to reduce the amount of material in structural components like blades and tower as the loads are reduced. The benefit is mainly to reduce the amount of material in blades and tower etc.

[0064] FIG. 2 discloses a table of the different parameters that are in use for controlling the wind turbine 4. Wind speed measurement is probably performed by a rotating wind measuring device which is often placed on the nacelle. The wind speed as such has a. defined area of operation. At very low wind speed, maybe less than 2 metres per second, a switch off of the system is probably performed because the wind speed will give less power than what the system as such is using. In the other end, at maximum wind speed, a reduction of the pitch angle will probably be performed if wind speeds exceed maybe 15 metres per second whereas at wind speed above 25 metres per second the wind turbine will be totally switched off. The yaw error 14 is an error that occurs if the direction of the wind changes. For continuous change in wind the yaw position of the nacelle will be adjusted. In situations where wind gust ride through exists, it is possible that the direction of the wind is changing rapidly. Here the yaw error will be increased to a relatively high value. The rotor speed 16 is of course a typically measured parameter in a wind turbine. The rotor speed probably also has a minimum and a maximum speed which are acceptable. Because a generator is directly coupled to the rotor speed by gear or directly coupled, the frequency of generated power will therefore probably be related to the rotor speed. But because the wind turbine probably comprises an inverter system the power is at first converted to direct current and afterwards into AC3 phased power with the correct frequency. Because the system is using the inverter technology, a relatively high span of rotor speed can be accepted.

[0065] The pitch angle 18 is adjusted for higher wind speed in order to reduce the power production of the wind turbine. Up to a certain wind speed the pitch will be regulated for maximal yield and after a certain limit, a gradual downwards regulation towards a feathered position will be performed.

[0066] Power production 20 is of course also a relatively important parameter that is measured. By the system as disclosed previously in this patent application, power production is by this system reduced in order to reduce the maximum load of the wind turbine.

[0067] Pitch regulation 22 the wind turbine comprises a pitch regulation system. This regulation system could be performed by electric motors or it could be produced by hydraulic devices.

[0068] Rotor acceleration 24 one of the more important parameters to be measured is situations where a rapid acceleration of the rotor takes place. Rotor acceleration can indicate wind gust just as effectively as maybe the wind speed sensor. Therefore, rotor acceleration is, for a fast operating system, rather important to be controlled. Pitch angle limit vector 26 is a limiting vector which is performed as a table based on wind speed and pitch angle. The system as such comprises a table where the two values are related to each other.

[0069] Wind speed vector 28 is simply a vector that is defined based on measuring of the wind speed.

[0070] A system for high yaw error and gust ride through load reduction can of course comprise further parameters as disclosed in the table shown in FIG. 2. The system as such is not limited to use all the defined parameters but in some situations full control of the system could be performed by only using some of the defined parameters.

[0071] Definition:

[0072] Wind direction: Actual wind direction

[0073] Yaw angle: Actual yaw position of the nacelle

[0074] Relative wind direction to nacelle direction: Actual wind direction measured at the nacelle defines the Yaw error.

REFERENCE NUMERALS

[0075] System (2)

[0076] wind turbine (4)

[0077] tower (6)

[0078] nacelle (8)

[0079] blade (10)

[0080] wind speed (12)

[0081] yaw error (14)

[0082] rotor speed (16)

[0083] pitch angle (18)

[0084] power production (20)

[0085] pitch regulation (22)

[0086] rotor acceleration (24)

[0087] pitch angle limit vector (26)

[0088] wind speed vector (28).