WO2019057550A1

WO2019057550A1 - Mutually supportive lidar system for wind turbines

Info

Publication number: WO2019057550A1
Application number: PCT/EP2018/074448
Authority: WO
Inventors: Henrik Stiesdal
Original assignee: Stiesdal A/S
Priority date: 2017-09-19
Filing date: 2018-09-11
Publication date: 2019-03-28

Abstract

The present invention relates to a mutually supportive Lidar system for wind farms comprising a data acquisition system operatively and communicative connected to two or more Lidar units. Each Lidar unit comprises orienting means in communication with a controller, and a Lidar. The Lidar is configured with an energy source emitting a beam and a sensor/processor unit configured for measurements of radial wind speeds.

Description

Mutually supportive Lidar system for wind turbines

Field of the Invention

The present invention relates to a mutually supportive Lidar system for wind farms comprising a data acquisition system operatively and communicative connected to two or more Lidar units. Each Lidar unit comprises orienting means in communication with a controller, and a Lidar. The Lidar is configured with an energy source emitting a beam and a sensor unit configured for measuring the radial wind speed at a given distance. Background of the Invention

Lidar systems are extensively used to mapping and have found widely use in meteorological applications for environmental and wind field mapping. The use of Lidars in connection with wind turbines for measuring wind conditions has been growing and Lidars are today widely used during the process of planning and establishing wind farms. In the recent years the use of Lidars during operation of the wind turbines has likewise been increasing.

Commercial Lidar systems are often based on a number of discrete telescopes oriented in fixed directions looking forward. The measurement range is typically limited to 80- 400 m, because the relatively small telescopes have limited aperture. To achieve Lidars with ranges in the upper part of the present-day scale it is necessary to use a high- powered laser.

In order to keep costs down, a single laser typically serves several telescopes. To ori- ent the beam towards the telescopes a so-called beam splitter may be used. A beamsplitter is an expensive and sensitive piece of equipment.

A range of commercial Lidar systems is used in relation to wind power. Nacelle- mounted Lidars may be used for upwind measurements for estimating the incoming wind to a wind turbine. Other systems have been proposed where the Lidar is mounted in the turbine spinner (nose cone), a so-called spinner-mounted Lidar. The advantage of spinner-mounted Lidars is that they can be designed to be reconfigured remotely in order to orient the beam at a larger or smaller angle relative to the axis of rotation, thereby covering a smaller or larger cone. The disadvantage of such systems is that the spinner-mounting makes it difficult to perform maintenance and repairs. Today, nacelle-mounted Lidars are mainly used today for testing purposes. Future use for commercial applications is expected to involve using Lidars to observe oncoming, large gusts, in particular so-called coherent gusts where a sharp rise in wind speed is associated with a simultaneous change in wind direction. Such gusts are generally causing the highest extreme loads on wind turbine blades. If their effect can be re- duced through the application of forward sensing techniques and appropriate turbine response means, it will be possible to design lighter and cheaper blades, or alternatively fit longer blades to existing wind turbine designs.

The disadvantage of such arrangement is that the requirements for system robustness and reliability are extremely high, because the wind turbine may experience severe overloading in case the Lidar is in a non-operational state or is providing incorrect information. In case of Lidar malfunction, a wind turbine designed to benefit from the advantages resulting from having knowledge of incoming wind conditions will need to be put into reduced operation mode or even stopped completely until the Lidar is inspected and possibly repaired. Today's commercially available Lidar systems struggle to meet the necessary robustness requirements.

Present-day nacelle-mounted Lidars have a limited cone angle of the observed field and are generally not able to observe gusts approaching the turbine from the side. For turbines fitted with longer blades under the assumption that all relevant gusts can be observed in time such side-approaching gusts may lead to significant risk of overload.

Present-day nacelle -mounted Lidars are typically oriented in the upwind direction to measure the incoming wind and are unable to observe the wind speed in the wake be- hind the turbine. It would be advantageous to make such observation, because it could be used for so-called wake steering. Wake steering is used to reduce the loads on downwind turbines and to increase their energy output. Using currently available technologies, measuring both the incoming wind and the wake typically requires two Lidars pointing in opposite directions. US 2015/0233962 A 1 describes an atmospheric measurement system for mapping wind fields in a wind farm. The system provides for simultaneous measurement of the wind upstream and downstream of a wind turbine using at least one Lidar with either a single Lidar beam split into two beams or a multiple beam Lidar with a first and a second beam source. Furthermore, a system comprising multiple Lidars is disclosed where the Lidar systems are operated dependent on each other by making use of the beam source in one Lidar and the sensor unit of another Lidar thereby achieving redundancy in the atmospheric measurement system.

Obj ect of the Invention

It is an objective of this invention to overcome one or more of the aforementioned shortcomings of the prior art.

Description of the Invention

The aforementioned aspects may be achieved by a mutually supportive Lidar system for wind farms. The mutually supportive Lidar system may comprise a data acquisition system operatively and communicatively connected to two or more Lidar units. Each Lidar unit may comprise a Lidar. Each Lidar unit may further comprise orienting means in communication with a controller. Each Lidar may be configured with an energy source emitting a beam and a sensor unit. Each Lidar may be configured for measuring radial wind speed at a given distance.

The sensor unit may be operatively connected to the energy source within each individual Lidar unit to detect scattered energy from the emitted beam, such that the indi- vidual Lidars can be configured to be operatively independent. The Lidar unit may be configured with a pivotable line of sight regulated by the orienting means substantially configured as a centerline of the emitted beam running from the energy source to a measurement point. The Lidar may be a pulsed Lidar or continuous wave (CW) Lidar.

The sensor unit may be a sensor/processor unit, wherein the sensor unit further comprises a processor. The Lidar measurements may comprise other wind conditions. The term wind conditions are applied as a general term in this description and thus, measuring wind conditions include measuring a radial wind speed. In one aspect the orienting means may be a gimbai. The gimbai may be configured with a ccontinuous 360 degree rotation of azimuth.

The orienting means is/are by no means limited to a gimbai. The orienting means may be configured with any given operational, rotation angle if the orienting means pro- vides for the Lidar units to serve the purpose of the mutually supportive Lidar system as described herein. The gimbai. may further be configured with, build-in elevation of the base. Present-day gimbals may provide ultra-precise angular position, rate and acceleration for development and production, testing of a wide range of systems. They may be used for directing optics, lasers, antennas and sensors at high speed to very precise pointing angles. Furthermore, present-day gimbals may require a minimum of maintenance.

In. one aspect the Lidar may comprise a substantially coherent energy source. Operating the individual Lidars independent means that the sensor unit and the energy source comprised in the same Lidar are operatively connected such that the sensor unit detects scattered energy from the emitted beam. This is contrary to dependent operated Lidars where the sensor unit of one or more Lidars may be operated to detect scattered energy from the beam emitted from another Lidar.

One effect of the embodiment may be that each Lidar unit may look in all directions of the forward hemisphere, thereby achieving to detect gusts approaching from the side. Another effect of the embodiment may be that the system may incorporate the "mutually Supportive Principle" or "Musketeer Principle" of one for all, all for one, where in case one Lidar unit fails, a neighboring Lidar unit may compensate for the absence of a valid Lidar signal by looking at the neighboring field and perform the measurement. Or alternatively several neighboring Lidar units may compensate for the ab- sence of a valid Lidar signal by jointly scanning the wind field in front of the failing Lidar unit. This may be advantageous by preventing the need for reduced operation of the wind turbine or wind turbines. Such compensation may be pre-programmed in the control of Lidar unit, so each Lidar is allocated a certain time slot looking forward of neighboring turbines, or allocation of time slots may be instructed during use from the data acquisition system. In either case the Lidar unit(s) may send the Lidar measurements results to the data acquisition system, which then calculates, maps or models the wind field in front of the failing Lidar unit and sends the results to the wind turbine for local control purposes. The local control purposes of the wind turbine may be correction of yaw misalignment, blade pitch or other rotor speed adjustments.

A further effect of the embodiment may be that one or more Lidar units may be oper- ated to measure radial wind speed at several measurement points and thus allocate their measurement time to different areas including pointing the beam in directions not within the forward hemisphere, thereby providing measurement to the data acquisition system. This may be advantageous in regard to achieving the establishment of a representation of the complete wind field in a wind farm, using the data acquisition system.

In one embodiment of the mutually supportive Lidar system, the orienting means is/are fitted with a beam-deflecting component oriented to face the energy source and the sensor unit and arranged to deflect the beam. In one aspect the beam-deflecting component may be a mirror or a prism.

In one aspect, the beam-deflecting component may be mounted on a gimbal.

An effect of the embodiment comprising the gimbal-mounted light-deflecting component may be that Lidar unit's line of sight may be pivotable adjusted achieved with the Lidar mounted in a fixed position. The gimbal-mounted light-deflecting component may provide for orienting the emitted beam in any direction within a hemisphere with any azimuth angle from 0 to 360 degree. The advantage may be that the Lidar unit using a single Lidar may be used to measure at measurement points upwind, downwind or sideways from the Lidar. In one embodiment of the mutually supportive Lidar system, the Lidar units are nacelle-mounted.

An effect of this embodiment is that the Lidar unit is mounted in the same height as the rotor and may emit a beam substantially perpendicular to the rotor plane thereby achieving a line of sight less sensitive to errors in its angular orientation. In general, nacelle-mounted Lidars have the advantage of being less sensitive to errors in its angular orientation compared to ground-based Lidars, because a nacelle -mounted Lidar typically has a line of sight substantially in the horizontal direction, and thus measures the incoming wind on the rotor plane as the cosine component. Contrary to this, the ground-based Lidars measures in a direction closer to a vertical direction typically with an oblique angel to the vertical, and thus measures the incoming wind on the rotor plane as the sine component. In one embodiment of the mutually supportive Lidar system, the individual Lidar units are mounted on selected wind turbines.

An effect of this embodiment is that mapping the wind field may be accomplished using a total of less than one Lidar per wind turbine in a wind farm, if the wind farm comprises at least three wind turbines to benefit from the mutually supportive system. This may be advantageous in regard to installation and maintenance costs. Furthermore, if the Lidar units are mounted in an optimized way, the mutually supportive system may provide for adequate coverage using less than one Lidar per wind turbine in a wind farm even in the case one or more Lidar unit fails.

In general, the effect of the mutually supportive system is that when a Lidar unit fails the other Lidar units assures adequate coverage to measure the relevant wind fields for all the relevant wind turbines, thereby achieving continued operation of all the relevant wind turbines during the downtime of a failing Lidar unit.

In one embodiment of the mutually supportive Lidar system, the Lidar unit comprises a telescope fitted to the Lidar. An effect of the embodiment is that a high-powered laser may be used with a simple optical unit comprising a single, large-aperture telescope to give accurate readings at long distances. This is advantageous in regard to eliminating the need for using any kind of beam splitters. In a further aspect, the large-aperture telescope may be adjust- able with the effect of adjusting the focus point and thereby achieving that the measurement point may be altered not only in angular direction but also in distance.

In one embodiment of the mutually supportive Lidar system, the data acquisition system collects wind data from the communicative connected Lidar units.

An effect of this embodiment is that the data acquisition system may collect all the data from all the communicative connected Lidar units thereby achieving a data set with a large amount of data to map the actual measured wind field covered by the system. It may be further advantageous in regard to establishing the base for further ex- trapolation to establish a representation of the complete wind field in a wind farm. Furthermore, the collected data may be used for predicting or forecasting wind fields in a local field or for a selected area.

In one aspect, the data acquisition system comprises a control system that communi- cates with the individual Lidar units to direct the Lidar beam to specified directions and/or distances, and a processing system that processes the collected wind data from one or more of the communicatively connected Lidars to create a wind field representation of a wind field for one or more selected areas. In one aspect the control system comprised in the acquisition system may configure the sensor unit to measure the radial wind speed at a given distance and/or in a given direction. The given distance and/or direction may be any specified distance and/or direction within the reach of the Lidar unit(s). In one aspect the selected area(s) is(are) upwind from one or more wind turbines, downwind from one or more wind turbines, sideways from one or more wind turbines and/or for the entire area of the wind farm. An effect of this embodiment is that the operation of each Lidar units may from time to time be altered to allocate time slots to measure in different direction and distances than their normal operation. These alterations may precisely may allocation of time slots and thus be incorporated as part of the normal operation. The operation of a Li- dar unit may include time slots allocated to determining local wind field for the turbine on which it is mounted, time slots allocated to measure neighboring wind field(s), time slots allocated to measure down wind, and/or time slots allocated to measure elsewhere to provide data for characterizing the complete wind farm wind field. This has the advantage that the time slots may be adjusted continuously as a consequence of conditions, failing neighboring Lidar units, wake steering needs, amongst others. The time slots may be adjusted both in regard to purpose and time length.

A further effect of this embodiment is the complete wind farm wind field may be mapped, which may advantageously be used for control purposes, such as wake steering. The mapping may comprise the measured data, a representation of the measured data including extrapolation of the data set, predicted or forecasted wind field based on the actual measured data or any other relevant model representation of the wind field based on the collected wind data.

In one aspect, when installed in a wind farm the mutually supportive Lidar system according to the invention comprises:

• A nacelle-mounted Lidar unit on each wind turbine or on selected turbines

• A telescope fitted to the Lidar

• A mirror, prism or other light-deflecting component mounted on a gimbal

• A control system that allows the beam from the individual Lidar units to be directed to specified directions and distances

• A data acquisition system that collects information from all the Lidar units in the wind farm

• A processing system that uses the information from all the Lidars to create a representation of the wind field in front of all the wind turbines and in the wind farm.

The installed system has the previously mentioned advantages. An object of the invention may be achieved by a method of mapping a wind field in a wind farm. The method may comprise an act of communicating between a data acquisition system and two or more Lidar units. The method may further comprise an act of operating two or more Lidar units from a data acquisition system. The operating act may include orienting the beam emitted by the individual Lidar units by use of orienting means. The orienting means may be in communication with a controller. The method may further comprise an act of measuring radial wind speed at a given distance and/or direction using independently operated Lidars. As previously described independently operated Lidars means that the sensor unit and the energy source comprised in the same Lidar are operatively connected such that the sensor unit detects scattered energy from the emitted beam. This is contrary to dependent operated Lidars where the sensor unit of one or more Lidars may be operated to detect scattered energy from the beam emitted from another Lidar.

The Lidars units may comprise orienting means. The orienting means may provide for an orienting angle of the Lidar and/or the Lidar beam. The orienting means may be configured with a continuous angle rotation of up to 360 degree rotation of azimuth. A further objective of the invention may be achieved by a method for mapping a wind field in a wind farm using a total of less than one Lidar per wind turbine.

One effect of the embodiment may be that in case one Lidar unit fails a neighboring Lidar unit may compensate for the absence of a valid Lidar signal by looking at the neighboring field and perform the measurement. Or alternatively several neighboring Lidar units may compensate for the absence of a valid Lidar signal by jointly scanning the wind field in front of the failing Lidar unit, hereby achieving a "mutually Supportive Principle" or "Musketeer Principle" of one for all, all for one. This may be advantageous by preventing the need for reduced operation of the wind turbine or wind tur- bines.

As previous described such compensation may be pre-programmed in the control of the Lidar unit(s), so each Lidar is allocated a certain time slot looking forward of neighboring turbines, or allocation of time slots may be instructed during use from the data acquisition system. In either case the Lidar unit(s) may send the Lidar measurements results to the data acquisition system, which then calculates, maps or models the wind field in front of the failing Lidar unit and sends the results to the wind turbine for local control purposes. The local control purposes of the wind turbine may be correction of yaw misalignment, blade pitch or other rotor speed adjustments.

A further effect of the embodiment may be that one or more Lidar units may be operated to measure wind conditions at several measurement points and thus allocate their measurement time to different areas including pointing the beam in directions not within the forward hemisphere, thereby providing measurement to the data acquisition system. This may be advantageous in regard to achieving the establishment of a representation of the complete wind field in a wind farm, using the data acquisition system.

A further objective of the invention may be achieved by a method for mapping a wind field in a wind farm using a mutually supportive Lidar system as described in the previous embodiments.

Effects and advantages of this embodiment may be in line with those previously described for the various embodiments previously described. Description of the Drawing

Figure 1 illustrates one embodiment of the mutually supportive Lidar system.

Figure 2 illustrates one embodiment of the Lidar unit.

Figure 3 illustrates one embodiment of the nacelle -mounted Lidar unit.

Figure 4 illustrates one embodiment of the mutually supportive Lidar system used in a wind farm.

Figure 5 illustrates on embodiment of the method for mapping a wind field in a wind farm.

Detailed Description of the Invention

No Item

1 mutually supportive Lidar system

2 Data acquisition system

4 Lidar unit 5 Lidar

6 Energy source

7 Sensor unit

8 Orienting means

9 Controller

10 Beam

11 Line of sight

12 Measurement point

14 Gimbal

20 Telescope

30 Beam-deflecting component

31 Mirror

32 Prism

40 Control system

42 Processing system

50 Wind data

52 Wind field representation

54 Wind field

55 Local field

56 Neighbour field

57 Wake

60 Selected area

100 Wind farm

101 First row

102 Second row

110 Wind turbine

111 First wind turbine

112 Second wind turbine

113 Third wind turbine

120 Nacelle

200 Method

210 Communicating

212 Operating

Figure 1 illustrates one embodiment of the mutually supportive Lidar system 1. The system is illustrated with two Lidar units 4 each comprising a Lidar 5 configured with a sensor unit 7 and an energy source 6. The Lidar emits a beam 10 with a line of sight 11. The line of sight 11 is illustrated by a dotted line. The line of sight is defined as the centre of the beam and extends from the energy source 6 to a measurement point 12 within a selected area 60. The selected area 60 is the area or part of the area for which the wind field 54 (not illustrated) is measured. The illustrated Lidar unit further comprises orienting means 8 - here illustrated as a gimbal 14 - mounted with a beam- deflecting component, such that the beam may be oriented in different directions and angles.

The Lidar units 4 are operatively and communicative connected to the data acquisition system 2. In the illustrated embodiment the correspondence is in both direction between the individual Lidar unit 4 and the data acquisition system 2. The figure further illustrates how additional Lidar units 4 may be added to the system with each operatively and communicative connected to the data acquisition system 2. The communication in the system may not be limited to this. Figure 2 illustrates one embodiment of the Lidar unit 4 comprising a Lidar 5, an optical element which here is a telescope 20 adapted to the Lidar 5, orienting means 8 - here illustrated as a gimbal 14 - mounted with a beam-deflecting component 30 and a controller 9 controlling the gimbal 8. The beam-deflecting component 30 may be a mirror 31 or a prism 32. The gimbal 8 may be pivotable adjustable in one or more directions. Here, the gimbal is illustrated to be pivotable around two non-parallel axes. Using a gimbal 8 as illustrated and described for this embodiment ensures that the Lidar unit 4 is configured with a pivotable line of sight 11 (illustrated in figure 1). Other embodiments may include that the gimbal 8 is mounted differently in the Lidar unit 4 but with the same purpose of achieving a Lidar unit 4 configured with a pivot- able line of sight.

Figure 3 illustrates one embodiment with a Lidar unit 4 mounted on the nacelle 120 of a wind turbine 110. The wind turbine is illustrated with the rotor plane of the blades and the wind hitting the blades front the front. The Lidar unit may measure the wind field upwind, which is in front of the rotor plane. The Lidar may measure the wind field in the opposite direction i.e. looking backwards to measure the wake. The Lidar may measure the wind field to the sides of the wind turbine 110 in either direction to measure the wind field hitting the rotor with a slanting direction to the rotor plane or even parallel to the nacelle or rotor plane.

Figure 4 illustrates one embodiment of the mutually supportive Lidar system used in a wind farm 100. The wind farm is illustrated with a first row 101 of wind turbines 110 and a second row 102 of wind turbines 110. Three of the wind turbines 110 in the first row 101 are each illustrated with a nacelle-mounted Lidar unit 4 with the lines of sight 11 illustrated to indicate which wind field 54 is measured.

The Lidar unit 4 on the first wind turbine 111 on the top left is illustrated to measure the local field 55 upwind from the wind turbine 110. The Lidar unit 4 on the second wind turbine 112 is illustrated to measure the neighbour fields 56 upwind from the respective wind turbines 110, here the first 111 and the third wind turbine 113.

The Lidar unit 4 on the third wind turbine 113 in the first row 101 is illustrated to measure the local field 55 surrounding the wind turbine 110, 113 - upwind and sideways for the incoming wind field and gusts, and downwind for the wake 57.

Figure 5 illustrates one embodiment of the method 200 for mapping a wind field in a wind farm. The method 200 comprises an act of communicating 210 between a data acquisition system 2 and two or more Lidar units 4. The method 200 further comprises an act of operating 212 two or more Lidar units 4 from the data acquisition system 2. Each Lidar unit 4 may comprise a Lidar which may be independently operated and used for measuring 214 wind conditions. The measurements may include measuring 214 radial wind speed at a given distance and/or direction. The Lidar units may com- prise orienting means, which may provide for an orienting angle of the Lidar and/or the Lidar beam.

Claims

A mutually supportive Lidar system (1) for wind farms (100) comprising a data acquisition system (2) operatively and communicatively connected to two or more Lidar units (4), wherein each Lidar unit (4) comprises a Lidar (5) configured with an energy source (6) emitting a beam (10) and a sensor unit (7), and wherein each Lidar unit (4) is configured with a line of sight (11) substantially configured as a centerline of the emitted beam (10) extending from the energy source (6) to a measurement point (12), and wherein said Lidar units (4) are configured for measuring radial wind speed at a given distance, wherein:

- the sensor unit (7) comprised in a Lidar (5) is operatively connected to the energy source (6) within the same Lidar (5) to detect scattered energy originating from the emitted beam (10), such that the individual Lidars (5) are configured to be operatively independent,

each Lidar unit

(4) comprises orienting means (8) in communication with a controller (9), said orienting means (8) being configured to pivotal regulate the line of sight (11).

A mutually supportive Lidar system (1) according to claim 1 wherein the orienting means (8) is a gimbal (14).

A mutually supportive Lidar system (1) according to one or more of the preceding claims wherein the orienting means (8) is/are fitted with a beam- deflecting component (30) oriented to face the energy source (6) and the sensor unit (7) and arranged to deflect the beam (10).

A mutually supportive Lidar system (1) according to claim 2 wherein the beam-deflecting component (30) is a mirror (31) or a prism (32).

5. A mutually supportive Lidar system (1) according to one or more of the preceding claims wherein the Lidar units (4) are nacelle-mounted.

6. A mutually supportive Lidar system (1) according to one or more of the preceding claims wherein the individual Lidar units (4) are mounted on selected wind turbines (110).

A mutually supportive Lidar system (1) according to one or more of the preceding claims wherein the Lidar units (4) comprise a telescope (20) fitted to the Lidar (5) comprised in the unit (4).

8. A mutually supportive Lidar system (1) according to one or more of the preceding claims wherein the data acquisition system (2) collects wind data (50) from the communicative connected Lidar units (4).

9. A mutually supportive Lidar system (1) according to one or more of the preceding claims wherein the data acquisition system (2) comprises a control system (40) that communicates with the individual Lidar units (4) to direct the Lidar beam

(10) to specified directions and/or distances, and a processing system (42) that processes the collected wind data (50) from one or more of the communicatively connected Lidars (5) to create a wind field representation (52) of a wind field (54) for one or more selected areas (60).

A mutually supportive Lidar system (1) according to claim 9 wherein the selected area(s) (60) is(are) upwind from one or more wind turbines (110), downwind from one or more wind turbines (110), sideways from one or more wind turbines (110) and/or for the entire area of the wind farm (100).

11. A method (200) of mapping a wind field (54) in a wind farm (100) comprising the acts of:

- Communicating (210) between a data acquisition system (2) and two or more

Lidar units (4) each Lidar unit (4) emitting a beam (10);

Operating (212) two or more Lidar units (4) from the data acquisition system (2), said operating includes orienting the beam (10) emitted by the individual Lidar units (4) by use of orienting means (8) in communication with a controller (9); and

Measuring (214) radial wind speed at a given distance and/or direction with two or more Lidar units (4) using independently operated Lidars (5).

12. A method (200) of mapping a wind field (54) in a wind farm (100) according to preceding claim 11 using a total of less than one Lidar (5) per wind turbine (110) in the wind farm (100).

13. A method (200) of mapping a wind field (54) in a wind farm (100) according to any one of preceding claims 11 or 12 using a mutually supportive Lidar system (1) according to any one or more of the preceding claims 1-10.