CA1245283A - Wind energy conversion system - Google Patents
Wind energy conversion systemInfo
- Publication number
- CA1245283A CA1245283A CA000519779A CA519779A CA1245283A CA 1245283 A CA1245283 A CA 1245283A CA 000519779 A CA000519779 A CA 000519779A CA 519779 A CA519779 A CA 519779A CA 1245283 A CA1245283 A CA 1245283A
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- CA
- Canada
- Prior art keywords
- wind
- propeller
- speed
- generator
- data processing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/72—Wind turbines with rotation axis in wind direction
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- Indicating Or Recording The Presence, Absence, Or Direction Of Movement (AREA)
Abstract
ABSTRACT
The wind energy conversion system includes a wind machine having a propeller connected to a generator of electric power, the propeller rotating the generator in response to force of an incident wind. The generator converts the power of the wind to electric power for use by an electric load. Circuitry for varying the duty factor of the generator output power is connected between the generator and the load to thereby alter a loading of the generator and the propeller by the electric load. Wind speed is sensed electro-optically to provide data of wind speed upwind of the propeller, to thereby permit tip speed ratio circuitry to operate the power control circuitry and thereby optimize the tip speed ratio by varying the loading of the propeller. Accordingly the efficiency of the wind energy conversion system is maximized.
The wind energy conversion system includes a wind machine having a propeller connected to a generator of electric power, the propeller rotating the generator in response to force of an incident wind. The generator converts the power of the wind to electric power for use by an electric load. Circuitry for varying the duty factor of the generator output power is connected between the generator and the load to thereby alter a loading of the generator and the propeller by the electric load. Wind speed is sensed electro-optically to provide data of wind speed upwind of the propeller, to thereby permit tip speed ratio circuitry to operate the power control circuitry and thereby optimize the tip speed ratio by varying the loading of the propeller. Accordingly the efficiency of the wind energy conversion system is maximized.
Description
33 t WIND ENERGY CONVERSION SYSTEM
BACI~GROllE~D OF l~E I~T:COI~
1. E'IE~D OF TEIE INVENTION
The present invention relates to wind ~nergy conversion systems, and more particularly to a control ystem for a wind machin~ that incorporates a laser Doppler anemometer to sense wind gust~
BACI~GROllE~D OF l~E I~T:COI~
1. E'IE~D OF TEIE INVENTION
The present invention relates to wind ~nergy conversion systems, and more particularly to a control ystem for a wind machin~ that incorporates a laser Doppler anemometer to sense wind gust~
2 . DESCRIP~ON OF 1~ PRIOR ART
It ~ w~ll known to u~e a wind mill or wind machine ~or the conver~ion o wind energy to elec ric~l en~rgy. One ~5;;~83 known con truction for ~uch a wind machine incl~des a rela~ively large propeller havinq a shaft ~hat i9 mechanically csupled to the Yhaft of an electric generator.
Wind inciden~ upon the propeller interacts aerodynamically wlth the propeller blade~ to impart forces thereon that rotate the propeller shaft and the generator shaft.
Generally the e~ficiency of a wind energy conversion machine is dependent upon the :atio of the speed of the wind to the tip speed of ~he propeller blade which is ba~ed on the radius of the blade and the angular rotation of the propeller. The rotational speed of the propeller i~
dependent upon both the wind speed and the magnitude of the electrical load being powered by the generator.
As is well known, an electrical load impart~ a torque which counteracts the torque induced by the wind. Thus, the load torque of the generator tend~ to 510w down the propeller rotation, while the wind torque tends to increase the rate of move~ent of the propeller. Consequently, the rate of rotation of the propeller can be varied for a given wind ~peed by altering the elec~rical load on the generator.
Such control of ~he propeller rotation rate and according~y the peed of the propeller blade tip permits adju~tment of the tip speed ratio for improved efficiency of the wind energy conversion process.
It ~ w~ll known to u~e a wind mill or wind machine ~or the conver~ion o wind energy to elec ric~l en~rgy. One ~5;;~83 known con truction for ~uch a wind machine incl~des a rela~ively large propeller havinq a shaft ~hat i9 mechanically csupled to the Yhaft of an electric generator.
Wind inciden~ upon the propeller interacts aerodynamically wlth the propeller blade~ to impart forces thereon that rotate the propeller shaft and the generator shaft.
Generally the e~ficiency of a wind energy conversion machine is dependent upon the :atio of the speed of the wind to the tip speed of ~he propeller blade which is ba~ed on the radius of the blade and the angular rotation of the propeller. The rotational speed of the propeller i~
dependent upon both the wind speed and the magnitude of the electrical load being powered by the generator.
As is well known, an electrical load impart~ a torque which counteracts the torque induced by the wind. Thus, the load torque of the generator tend~ to 510w down the propeller rotation, while the wind torque tends to increase the rate of move~ent of the propeller. Consequently, the rate of rotation of the propeller can be varied for a given wind ~peed by altering the elec~rical load on the generator.
Such control of ~he propeller rotation rate and according~y the peed of the propeller blade tip permits adju~tment of the tip speed ratio for improved efficiency of the wind energy conversion process.
-3- ~L2~L5~83 ~ common problem arising in the use of wind machines i5 the unpredictable variations of wind speed that result in corresponding variations in the tip speed ratio. Thi~
pro~lem is of part~cular concern in the case of wind gus~s wherein the wind speed changes far more rapidly than the propeller can change its rotational cpeed. A-~ a result, the efficiency of the wind energy conversion proce~ usually d~creaRes when there are variable wind speeds and i5 ~ignificantly affected by wînd gusts.
One method of dealing with the problem of variable wind speed and wind gust~ is to employ mechanical anemometers upwind o~ the wind machine to measure the wind intensity. Such measurements provide advance information about wind speed which can then be utilized to alter the electrical load on the generator so as to optimize the tip speed ratio.
However, it has been found that the wind receptor cup~ of mechanical anemome~ers have significant inertia which retards the transmission of the wind speed information. Such delay hampers the ability to accurately control the tip speed ratio.
A further drawback in the u~e of mechanical anemometers is tbat such anemometers measure wind speed only at the site of the anemome~er. Since wind speed _4~ 83 measurements can vary markedly from point to point, the wind speed data obtained by use of a single mechanical anemometer may be inadequate and may not properly describe the wind condition which will be experienced by the propeller of the wind machine.
Thus a mechanical anemometer does not adequately provide the information needed to attain optimum control of the tip speed ratio.
SUMMARY OF THE INVENTION
Against the foregoing background the invention seeks to provide a novel, high efficiency wind energy conversion system.
Further, the invention seeks to effectively control the propeller tip speed of a wind machine in response to sensed wind speed without the disadvantages inherent in mechanical anemometers.
Still further, the invention seeks to control the propeller tip speed of the wind machine by varying the electrical load of a generator connected to the propeller in response to wind speed data obtained by laser Doppler measurement of wind speed.
One broad aspect of the invention pertains to a wind energy conversion system comprising a propeller rotatable by force of wind, a generator of electricity mechanically coupled to the propeller for converting power of the wind to electric power for use by an electric load, and means coupled between the generator and the electric load for varying the electric power drawn by the electric load to alter the electric loading of the generator.
Means are provided for electro-optically sensing the speed of the wind at a location upwind from the propeller and means is coupled between the sensing means and the power varying means for operating the power varying means to adjust the electric load of the generator in accordance with a sensed value of ;~
. ~
5 ~ 5~
wind speed to thereby obtain a desired ratio of wind speed to the speed of a tip of a blade of the propeller.
Additional aspects, advantages and novel features of the invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by the practice of the invention. The aspects and the advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other aspects, and in accord-ance with the purpose of the present invention, as embodied and broadly described herein, the wind energy conversion system comprises a propeller rotatable by the force of wind, and a generator of electricity mechanically coupled to the propeller.
The generator serves to convert the power of the wind to electric power for use by an electric load. Circuitry for varying the power applied to the load is coupled between the generator and the load, the circuitry permitting adjustment of the loading of the generator to attain a desired ratio of wind speed to the tip speed of the propeller blade. Also included in the invention is an electro-optic subsystem for the sensing of the wind speed at various locations upwind of the propeller, an output of the subsystem being used to operate the circuitry for varying the loading on the generator. The response time of the electro-optic sensing is significantly faster than that associated with mechanical anemometers so as to provide the capability of maintaining a desired tip speed ratio even in the presence of gusty winds.
, ~
8RIEF DB5CRIPTIO~ OF T~B DRA~I~GS
The accompanying drawings of the wind energy conver~ion sy~tem whl~h are incorporated in and form a part o~ the -~pecification illustrate a preferred embodimen~ of the present invention, and together with the description, serve to explain the prlnciples of the invention. In the drawing~:
F~G. 1 is a bloc~ diagram of a wind energy conversion system with electro-optic sensing of wind speed for co~trol of the.tip speed ratio that incorporates one embodiment of the invention; and, FIG. 2 is a block diagram of a wind measuring subsy tem thereof comprising laser beam transmission and reception equipment, and digital storag~ and correlation circuitry for mea~urement of Doppler frequency shift a~sociated with moving particles in air.
Corresponding reference characters indicate corresponding part~ throughout the several views of the drawings.
20D~TAIL~N D~SCRIP~IO~ OF T~E PR~F~RR~D ~MBODI~T
A wind energy conver ion ~ystem incorporat~ng a preferred embodiment o~ the inven~ion i~ generally indica~ed - by the reference numb~r 20 in Fig. 1.
i283 The wind energy conversion ~ys~em 20 includes a wind mill or machine 22 which ~n~eracts wlth the wind, indicated by an arrow 24, for driving an electric generator 26. ~he wînd machine 22 i-~ hown ln stylized view, and includes a propeller 28 moanted on a propeller shaft 30 set on top o~ a tower 32. ~he shaft 30 i~ mechanically coupledt via dashed llne 34, to the generator 26, as well a~ to a sensor 36 of the angular velocity of the shat 3Q0 The genera~or 26, which may be an alternator providing three-pha~e current, 10~ via wire~ 38, connects with a load 40 via power-control circuitry 42.
A wind measuring sub~ystem 44 is included within the energy conversion system 20 for sensing the pre~ence of wind gusts, as indicated by the arrow 46, upwind of the machine 22. The subsy~tem 44 provides a measure of the wind speed associa~ed with such gusts and, with reference to Fig. 2~
includes a laser beam transmitter 48, a laser beam receiver 50 and a digital data processor 5~.
The proce~sor 52 i~ coupled to the transmitter 48 and the receiver 50 for the extraction of wind speed data a~ociated wlth Doppler frequency shift imparted to a la~er beam by moving particle aerosols 53 in the gu ting air upwind of the machine 22, the aerosole 53 acting a~ scatterer~0 . ..
~245Z83 The system 20 further compri3es electrical circuitry 54 for the determination of the actual tip ~peed ratio, an ad~ustable source 56 of a reference voltage s$gn~1 serving a~ a reference tip speed, a ~umming device 58 and an integrator 60. The ~ip peed circuitry 54 can include well-known circul~ry, ~uch as that ~ound in a microproces~or, for the division of one electrical signal by a second electrical 8~ gnal o prov$de an output electrical signal on ~he line 62 repre~enting the ratio of the speed of the wind to the ~peed of the blade tip of the propeller 28~
In operation, the wind measuring subsyqtem 44 provide~ an output signal on the line 64 representing the mea~ured speed of a wind gust 46 prior to the time when the gu3t 46 reaches the propelle~ 28. The shaft speed qensor 36, which can include a known shaft angle encoder or tachometer, provides an output electrical ~ignal on line 66 which i3 proportional to the angular rate of rotation of the shaft 30 and the propeller 28, the signal on the line 66 also being proportional to the tangential speed of each blade tip of the propeller 28.
The ratio circu$try 54 divides the ~ignal on the line 64 by the ~ignal on the line 66 to provide a ratio ~ignal via the line 62, which 18 coupled to a negative input terminal of the summing device 58. The reference signal of -;Z~33 _g_ the -qource 56 is applied to a positive input terminal of the ~umming device 58~ Thu~ the summing device 58 applies an error signal to the integrator 60, the error 9ignal being a mea~ure of the difference between a desired or re~erence Yalue of the tip speed ratio and the anticipated ratic at the time the propeller 28 receives the wind gust 46.
The int~grator 60 integrates the error signal of th~
summing device 5~ in accordance with well-known principle~
of feedback control theory, to produce a drive signal on the line 68 for operating the power control circuitry 42. The circuitry 42 can include a known silicon control rectifier (SCR) circuit connected to each o~ the wires 38, the control terminal of each of the SCRs being driven by the drive ~ignal on the line 6~. Tbe drive signal on the line 68 establishes the duty cycle in the extraction of alternating current from the wire~ 38 and hence, the average power delivered by the generator 26 via the circuitry 42 to the load 40.
It should be noted that the coupling of electric power from ~he generator 26 to the load 40 introduces a retarding torque which tend~ to 910w down the rotational speed of ~he generator and, a3 a consequence, the rota ional ~peed of the propeller shaft~ Thu~, the re~arding ~orque of the generator 26 tends to counteract the torque induced on the propeller 28 by action o~ the wind impinging thereon.
~L~45Z~3 , rt can also be appreciated that a reduction in ~he duty cycle of the output current of the generator 26 permit~
the propeller shaft 30 to speed up, while an increase in ths duty cycle of the output curren~ of the generator 26 causes a decrease in the speed of the propeller shaft 30.
Consequently, variations in the magnitude of the drive signal on the line 68 can produce changes in the rotational cpeed of the shaft 30. In thiR manner, the drive signal i~
used to adjust the speed of the shaft 30 so a~ to provid~
the desired ratio between the wind speed and the tip speed o the propeller b~ades. A ratio of approximately unity is desirable in that it maximizes the efficiency of the conversion o~ the wind energy or power to the electric energy or power.
The response o~ the propeller 28 to a change in load torque accomplished by the power-control circuitry 42 depends on the inertia of the propeller 28, the generator 26 and the connecting mechanical apparatus~ The integrator 60, which may be fabricated as a low pass filter slows down the re~ponse of the feedback loop configura~ion of the system 20. This slowdown ta~es into account the response time of the propeller 28, so as to in~ure a controlled oscillation free transition in propeller speed and the proce~ of ad~u tment in the tip speed ratio. Such closed-loop ~peed . , .
-~` 3l2~5~83 control concept3 are known and accordingly need not be de~cribed herein. The sy3~em 20 therefore adjusts the tip-speed ratio by alteration of the electrical load on the generator 26.
The correction of the tip speed ratio i~ based on the anticipated wind peed, as measured at a time a~d location prior to the arrival of a wind gust at the propeller 28.
The prior knowledge o~ the wina speed i3 attained with the aid of the wind measuring sub~ystem 44 which operate3 by mean~ of photo~electric circuitry including the laser transmitter 48 and the receiver S0.
Referring now to Fig. 2, the details of the construction and operation of the subsystem 44 will now be described in connection with the laser tran mitter 48, the laser receiver 50 and the data proce~sor 52 previou~ly described with reference to Fig. 1.
The laser beam transmitter 48 includes a laser 70, a modulator 72 for pulsing the beam of light from the laser 70t and a beam deflector 74 which deflecks the pulsed beam of light from the modulator 72 over a predetermined ~can angle.
The light @xiting the beam deflector 74 i3 directed to the reg~on of the aerosol~ 53. ~he beam deflector 74 ca~
include an oscillating mirror (not shown) but preferably .
1~4~283 comprises an acousto-optic Bragg cell 76 driven by a piezoelectric transducex 78 activated by a radio frequency (RF) drive~ 80. The transducer 78 i5 located at one end of the cell 76 and a sonic ab~orber 82 is located at the opposite end of the cell 76. ~coustic waves are generated within the ~ranspare~t material of the cell 76 and are absorbed by ~he absorber 82.
Interaction of the light wave from the laser 70 with the acoustic wave from the tran~ducer 78 results in a known deflection of the light beam. A generator 84 applies an R~
~ignal to the driver 80, the R~ signal being of suitable frequecy for deflecting the light beam in a desired direction. A timing unit 86 in the data proces~or 52 provides timing ~ignals for synchronizing the operatlons of the generator 84 and the modulator 72 with operation of the processor 52.
The beam receiver 50 comprises a lens assembly 88 having a field lens 90 and an objective lens 92, a line filter 94 and a four-quadrant detector 96. Light from the laser 70 impinges upon the aerosols 53 and is reflected back to the lens assembly 88, which direct~ the received light through the filter 94 to focus upon the detector 96.
The len~ a~sembly 88 pas3es light at ~he original ~requency of the laser 70, as W211 as light which has been ~ 2 8 shifted in frequency by a Doppler frequency shift associatéd with motion of the aerosols 53. While there i~ a measure of random movement as ociated with the aerosols 53, there i al30 a bulk movement a~sociated with air movement or wind.
Accordingly, the Doppler shift contains data as to the wind speed.
The region of focus of the received light upon the detector 96 varies in accordance with ~he region of the air illuminated by the scanned beam from the deflector ~4. The ~canning beam illuminates a much larger region of space than would a stationary beam, and thereby provides speed data ~rom a much larger region of space than could be provlded by a single mechanical anemometer. The location of the region of focu~ of the received light on the detector 96 corresponds to the region of space which has been illuminated by the scanned beam from the deflector 74.
The four quadrants o~ the detector 96 are numbered 1, 2, 3, and 4, each of the quadrants being connected to corresponding channel~ of a four-channel amplifier 98. T~e detector 96 has x and y axe~ ~uperimpo4ed to identify a two-dimensional display of dat~ from the scanned reg~on. The .
detector 96 and the amplifler 98 can include a known photo-electron emis-qive material and a set of photo multipliers (not shown) whereby a set of four output signal~ are .
12a~5z~
obtained corresponding to tbe illumination of each o~ the four quadrants. The output signals of the amplifier 98 are applied to a channel ccmbiner 100 of the data proces~or 52.
The line filter 9~ is of known con~truction and filters oot or attenua~e~ optical energy at the tran~misslon frequency of the laser 70. In th~ absence of any Doppler shift, a minimum intenqity of light is reoeived at the detector 96 becau e substan~ially all of ~he optîcal energy is filtered out by the filter 94.
The optical configuration of the laser beam receiver 50 mitigates the effect~ of received beam wander induced by atmospheric variation~ in the refractive index due to temperature gradients in the air.
In the presence of Doppler shift, the energy associated with the optical spectrum of the shifted frequencies passes through the filter 94 to impinge upon the detector 96. Consequently, the four output signals of the amplifier 98 provide information both as to the location of sources of Doppler ~requency shift as well as the amount of such hift. In addition, the use of the filter 94 prevents overloading of the detector 96 and the amplifier 98 so as to perm~t these COmpOQent~ to be adjusted for a maximum sensitivity at the anticipated Doppler frequencies, The data processor 52 combines the aforementioned ~ timing u~i~ 86 and the channel combiner 100, and further includes a pair o ~ilters 102 and a pair of ~ignal samplers 104 connected to output channel~ of the combiner 100. Also included within the data processor 52 are a storage unit 106, a correlator 108, a Fourier transformer 110 and a di criminator 112. The ~amplers 104~ the skorage unit 106 and the correlator 108 are operated by clock signals of a clock (not shown~ within the timing unit 86.
In operation9 the combiner 100 sums together the quadrant signals of the right and the left sides of the detector 96 and outputs their di~ference a~ the output x channel signal. Similarly, the combiner 100 su~s together the signals of the upper and lower quadrants of the detector 96, and outputs their difference as the y channel signal.
The filters 102 filter the a~and y ou~put signal of the comblner 100, the filters 102 being band-pas~ filters which limit the spectrum of the received signals to the band of interest, thereby improving the signal-to-noise ratio. The samplers 104 provide digital sampling of the x and y channel signals from the filters 102, the digital samples being stored in sections 114 of the memory 106.
Ag portrayed in a graph 116 in the.block of the correlator 108, a sucoession of samples of the Doppler ~hifted ~ignal ls taken by each of the samplers 104. These sample~ ~re then correlated agains~ themselves, an ~z~s2a3 autocorrela~ion by ~he correlator 108 to produce an output correlation function containing the desired wind speed data.
The correlation may be done separately for the x and the y channel~, and may al50 be done a~ a cross correlation be ween the x and the y channels.
The extraction of Doppler data by means of the correlation operation i~ de cribed in the article ~Measuremenk of Cro~ Wind Velocity~ by F. Durst et al, Applied Optics, Vol. ~1, No. 14, July lSr 1982~ page~ 2596-2607.
The spectral components of the correlation functions are obtained by the transformer 110 which may be implemented as a well-known fast-Fourier transformation. An amplitude discriminator 112 selects the frequency components having the largest amplitudes as being representative of the wind speed. The amplitude of the wind speed appears as an output signal of the discriminator 112 on the line 64 to be applied to the circuitry 54 (Fig. 1) for calculation of the tip speed ratio.
In the selection of sample~ for the correlation, it may be desirable to u~e only those amples appearing within a preselected time interval after the transmis~ion of a pulse o~ laser light. Such a gelection of 3amples provides the function of range gating for mea~urement of wind cpeed - ~4L5Z~ ~
at a pre~elected range ~rom the propeller 28. As a practical ma~ter, in 'che implementation of the data proces or 52, the function3 of the correlator 108, the transmitter 110, and the descriminator 112 can readily be attained by use of a microprocessor which is suitably programmed to provide the fore~oing functions.
~ umerous programs for correlation, Fourier transformation and selection of signal~ based on amplitude are available for use with commercially available 10 mlcroprocessorY.
By means of the foregoing system, the loadiny of a wind operated electrical generator can be altered in accordance with infor~ation of future wind speed, the information being obtained before a gust of wind reaches the propeller of a wind machine. Such alteration of the loading of the generator, and thus of the propeller itself, permits adjustment of the tip speed ratio of the propeller blades so as to operate the wind machine efficiently by adapting the speed of the propeller to match the wind speed. Thereby, there i~ a more efficient conversion of wind energy to electrical energy.
The use of electro-op~ic Doppler measurement technique~ of a volume of air upwind of the wind machine, in combination with data processing of received Doppler -~ ~ 4 slgnal echoes permit~ a rapid measurement o the wind speed.
~he rapidity of measurement permits adjustment sf the electrlcal loading to be accompli~hed before any wind gu~t reache~ the propeller. Al~o the employment of electro-optic scanning of the la~er beam permits the gathering of data over a much larger area of space than can be obtained by mechanical anemometers.
The foregoing 1~ considered as illustrative only of the principles of the invention. ~urther, since numerouq modi~lcations and change~ will readily occur to ~ho~e skilled in the art, it i5 not desirable to limit the invention to the exact construction and operation shown and de3cribed, and accordingly all suitable modifications and equivalents may be resorted to falling within the scope o the invention as defined by the claims which follow.
.......
pro~lem is of part~cular concern in the case of wind gus~s wherein the wind speed changes far more rapidly than the propeller can change its rotational cpeed. A-~ a result, the efficiency of the wind energy conversion proce~ usually d~creaRes when there are variable wind speeds and i5 ~ignificantly affected by wînd gusts.
One method of dealing with the problem of variable wind speed and wind gust~ is to employ mechanical anemometers upwind o~ the wind machine to measure the wind intensity. Such measurements provide advance information about wind speed which can then be utilized to alter the electrical load on the generator so as to optimize the tip speed ratio.
However, it has been found that the wind receptor cup~ of mechanical anemome~ers have significant inertia which retards the transmission of the wind speed information. Such delay hampers the ability to accurately control the tip speed ratio.
A further drawback in the u~e of mechanical anemometers is tbat such anemometers measure wind speed only at the site of the anemome~er. Since wind speed _4~ 83 measurements can vary markedly from point to point, the wind speed data obtained by use of a single mechanical anemometer may be inadequate and may not properly describe the wind condition which will be experienced by the propeller of the wind machine.
Thus a mechanical anemometer does not adequately provide the information needed to attain optimum control of the tip speed ratio.
SUMMARY OF THE INVENTION
Against the foregoing background the invention seeks to provide a novel, high efficiency wind energy conversion system.
Further, the invention seeks to effectively control the propeller tip speed of a wind machine in response to sensed wind speed without the disadvantages inherent in mechanical anemometers.
Still further, the invention seeks to control the propeller tip speed of the wind machine by varying the electrical load of a generator connected to the propeller in response to wind speed data obtained by laser Doppler measurement of wind speed.
One broad aspect of the invention pertains to a wind energy conversion system comprising a propeller rotatable by force of wind, a generator of electricity mechanically coupled to the propeller for converting power of the wind to electric power for use by an electric load, and means coupled between the generator and the electric load for varying the electric power drawn by the electric load to alter the electric loading of the generator.
Means are provided for electro-optically sensing the speed of the wind at a location upwind from the propeller and means is coupled between the sensing means and the power varying means for operating the power varying means to adjust the electric load of the generator in accordance with a sensed value of ;~
. ~
5 ~ 5~
wind speed to thereby obtain a desired ratio of wind speed to the speed of a tip of a blade of the propeller.
Additional aspects, advantages and novel features of the invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by the practice of the invention. The aspects and the advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other aspects, and in accord-ance with the purpose of the present invention, as embodied and broadly described herein, the wind energy conversion system comprises a propeller rotatable by the force of wind, and a generator of electricity mechanically coupled to the propeller.
The generator serves to convert the power of the wind to electric power for use by an electric load. Circuitry for varying the power applied to the load is coupled between the generator and the load, the circuitry permitting adjustment of the loading of the generator to attain a desired ratio of wind speed to the tip speed of the propeller blade. Also included in the invention is an electro-optic subsystem for the sensing of the wind speed at various locations upwind of the propeller, an output of the subsystem being used to operate the circuitry for varying the loading on the generator. The response time of the electro-optic sensing is significantly faster than that associated with mechanical anemometers so as to provide the capability of maintaining a desired tip speed ratio even in the presence of gusty winds.
, ~
8RIEF DB5CRIPTIO~ OF T~B DRA~I~GS
The accompanying drawings of the wind energy conver~ion sy~tem whl~h are incorporated in and form a part o~ the -~pecification illustrate a preferred embodimen~ of the present invention, and together with the description, serve to explain the prlnciples of the invention. In the drawing~:
F~G. 1 is a bloc~ diagram of a wind energy conversion system with electro-optic sensing of wind speed for co~trol of the.tip speed ratio that incorporates one embodiment of the invention; and, FIG. 2 is a block diagram of a wind measuring subsy tem thereof comprising laser beam transmission and reception equipment, and digital storag~ and correlation circuitry for mea~urement of Doppler frequency shift a~sociated with moving particles in air.
Corresponding reference characters indicate corresponding part~ throughout the several views of the drawings.
20D~TAIL~N D~SCRIP~IO~ OF T~E PR~F~RR~D ~MBODI~T
A wind energy conver ion ~ystem incorporat~ng a preferred embodiment o~ the inven~ion i~ generally indica~ed - by the reference numb~r 20 in Fig. 1.
i283 The wind energy conversion ~ys~em 20 includes a wind mill or machine 22 which ~n~eracts wlth the wind, indicated by an arrow 24, for driving an electric generator 26. ~he wînd machine 22 i-~ hown ln stylized view, and includes a propeller 28 moanted on a propeller shaft 30 set on top o~ a tower 32. ~he shaft 30 i~ mechanically coupledt via dashed llne 34, to the generator 26, as well a~ to a sensor 36 of the angular velocity of the shat 3Q0 The genera~or 26, which may be an alternator providing three-pha~e current, 10~ via wire~ 38, connects with a load 40 via power-control circuitry 42.
A wind measuring sub~ystem 44 is included within the energy conversion system 20 for sensing the pre~ence of wind gusts, as indicated by the arrow 46, upwind of the machine 22. The subsy~tem 44 provides a measure of the wind speed associa~ed with such gusts and, with reference to Fig. 2~
includes a laser beam transmitter 48, a laser beam receiver 50 and a digital data processor 5~.
The proce~sor 52 i~ coupled to the transmitter 48 and the receiver 50 for the extraction of wind speed data a~ociated wlth Doppler frequency shift imparted to a la~er beam by moving particle aerosols 53 in the gu ting air upwind of the machine 22, the aerosole 53 acting a~ scatterer~0 . ..
~245Z83 The system 20 further compri3es electrical circuitry 54 for the determination of the actual tip ~peed ratio, an ad~ustable source 56 of a reference voltage s$gn~1 serving a~ a reference tip speed, a ~umming device 58 and an integrator 60. The ~ip peed circuitry 54 can include well-known circul~ry, ~uch as that ~ound in a microproces~or, for the division of one electrical signal by a second electrical 8~ gnal o prov$de an output electrical signal on ~he line 62 repre~enting the ratio of the speed of the wind to the ~peed of the blade tip of the propeller 28~
In operation, the wind measuring subsyqtem 44 provide~ an output signal on the line 64 representing the mea~ured speed of a wind gust 46 prior to the time when the gu3t 46 reaches the propelle~ 28. The shaft speed qensor 36, which can include a known shaft angle encoder or tachometer, provides an output electrical ~ignal on line 66 which i3 proportional to the angular rate of rotation of the shaft 30 and the propeller 28, the signal on the line 66 also being proportional to the tangential speed of each blade tip of the propeller 28.
The ratio circu$try 54 divides the ~ignal on the line 64 by the ~ignal on the line 66 to provide a ratio ~ignal via the line 62, which 18 coupled to a negative input terminal of the summing device 58. The reference signal of -;Z~33 _g_ the -qource 56 is applied to a positive input terminal of the ~umming device 58~ Thu~ the summing device 58 applies an error signal to the integrator 60, the error 9ignal being a mea~ure of the difference between a desired or re~erence Yalue of the tip speed ratio and the anticipated ratic at the time the propeller 28 receives the wind gust 46.
The int~grator 60 integrates the error signal of th~
summing device 5~ in accordance with well-known principle~
of feedback control theory, to produce a drive signal on the line 68 for operating the power control circuitry 42. The circuitry 42 can include a known silicon control rectifier (SCR) circuit connected to each o~ the wires 38, the control terminal of each of the SCRs being driven by the drive ~ignal on the line 6~. Tbe drive signal on the line 68 establishes the duty cycle in the extraction of alternating current from the wire~ 38 and hence, the average power delivered by the generator 26 via the circuitry 42 to the load 40.
It should be noted that the coupling of electric power from ~he generator 26 to the load 40 introduces a retarding torque which tend~ to 910w down the rotational speed of ~he generator and, a3 a consequence, the rota ional ~peed of the propeller shaft~ Thu~, the re~arding ~orque of the generator 26 tends to counteract the torque induced on the propeller 28 by action o~ the wind impinging thereon.
~L~45Z~3 , rt can also be appreciated that a reduction in ~he duty cycle of the output current of the generator 26 permit~
the propeller shaft 30 to speed up, while an increase in ths duty cycle of the output curren~ of the generator 26 causes a decrease in the speed of the propeller shaft 30.
Consequently, variations in the magnitude of the drive signal on the line 68 can produce changes in the rotational cpeed of the shaft 30. In thiR manner, the drive signal i~
used to adjust the speed of the shaft 30 so a~ to provid~
the desired ratio between the wind speed and the tip speed o the propeller b~ades. A ratio of approximately unity is desirable in that it maximizes the efficiency of the conversion o~ the wind energy or power to the electric energy or power.
The response o~ the propeller 28 to a change in load torque accomplished by the power-control circuitry 42 depends on the inertia of the propeller 28, the generator 26 and the connecting mechanical apparatus~ The integrator 60, which may be fabricated as a low pass filter slows down the re~ponse of the feedback loop configura~ion of the system 20. This slowdown ta~es into account the response time of the propeller 28, so as to in~ure a controlled oscillation free transition in propeller speed and the proce~ of ad~u tment in the tip speed ratio. Such closed-loop ~peed . , .
-~` 3l2~5~83 control concept3 are known and accordingly need not be de~cribed herein. The sy3~em 20 therefore adjusts the tip-speed ratio by alteration of the electrical load on the generator 26.
The correction of the tip speed ratio i~ based on the anticipated wind peed, as measured at a time a~d location prior to the arrival of a wind gust at the propeller 28.
The prior knowledge o~ the wina speed i3 attained with the aid of the wind measuring sub~ystem 44 which operate3 by mean~ of photo~electric circuitry including the laser transmitter 48 and the receiver S0.
Referring now to Fig. 2, the details of the construction and operation of the subsystem 44 will now be described in connection with the laser tran mitter 48, the laser receiver 50 and the data proce~sor 52 previou~ly described with reference to Fig. 1.
The laser beam transmitter 48 includes a laser 70, a modulator 72 for pulsing the beam of light from the laser 70t and a beam deflector 74 which deflecks the pulsed beam of light from the modulator 72 over a predetermined ~can angle.
The light @xiting the beam deflector 74 i3 directed to the reg~on of the aerosol~ 53. ~he beam deflector 74 ca~
include an oscillating mirror (not shown) but preferably .
1~4~283 comprises an acousto-optic Bragg cell 76 driven by a piezoelectric transducex 78 activated by a radio frequency (RF) drive~ 80. The transducer 78 i5 located at one end of the cell 76 and a sonic ab~orber 82 is located at the opposite end of the cell 76. ~coustic waves are generated within the ~ranspare~t material of the cell 76 and are absorbed by ~he absorber 82.
Interaction of the light wave from the laser 70 with the acoustic wave from the tran~ducer 78 results in a known deflection of the light beam. A generator 84 applies an R~
~ignal to the driver 80, the R~ signal being of suitable frequecy for deflecting the light beam in a desired direction. A timing unit 86 in the data proces~or 52 provides timing ~ignals for synchronizing the operatlons of the generator 84 and the modulator 72 with operation of the processor 52.
The beam receiver 50 comprises a lens assembly 88 having a field lens 90 and an objective lens 92, a line filter 94 and a four-quadrant detector 96. Light from the laser 70 impinges upon the aerosols 53 and is reflected back to the lens assembly 88, which direct~ the received light through the filter 94 to focus upon the detector 96.
The len~ a~sembly 88 pas3es light at ~he original ~requency of the laser 70, as W211 as light which has been ~ 2 8 shifted in frequency by a Doppler frequency shift associatéd with motion of the aerosols 53. While there i~ a measure of random movement as ociated with the aerosols 53, there i al30 a bulk movement a~sociated with air movement or wind.
Accordingly, the Doppler shift contains data as to the wind speed.
The region of focus of the received light upon the detector 96 varies in accordance with ~he region of the air illuminated by the scanned beam from the deflector ~4. The ~canning beam illuminates a much larger region of space than would a stationary beam, and thereby provides speed data ~rom a much larger region of space than could be provlded by a single mechanical anemometer. The location of the region of focu~ of the received light on the detector 96 corresponds to the region of space which has been illuminated by the scanned beam from the deflector 74.
The four quadrants o~ the detector 96 are numbered 1, 2, 3, and 4, each of the quadrants being connected to corresponding channel~ of a four-channel amplifier 98. T~e detector 96 has x and y axe~ ~uperimpo4ed to identify a two-dimensional display of dat~ from the scanned reg~on. The .
detector 96 and the amplifler 98 can include a known photo-electron emis-qive material and a set of photo multipliers (not shown) whereby a set of four output signal~ are .
12a~5z~
obtained corresponding to tbe illumination of each o~ the four quadrants. The output signals of the amplifier 98 are applied to a channel ccmbiner 100 of the data proces~or 52.
The line filter 9~ is of known con~truction and filters oot or attenua~e~ optical energy at the tran~misslon frequency of the laser 70. In th~ absence of any Doppler shift, a minimum intenqity of light is reoeived at the detector 96 becau e substan~ially all of ~he optîcal energy is filtered out by the filter 94.
The optical configuration of the laser beam receiver 50 mitigates the effect~ of received beam wander induced by atmospheric variation~ in the refractive index due to temperature gradients in the air.
In the presence of Doppler shift, the energy associated with the optical spectrum of the shifted frequencies passes through the filter 94 to impinge upon the detector 96. Consequently, the four output signals of the amplifier 98 provide information both as to the location of sources of Doppler ~requency shift as well as the amount of such hift. In addition, the use of the filter 94 prevents overloading of the detector 96 and the amplifier 98 so as to perm~t these COmpOQent~ to be adjusted for a maximum sensitivity at the anticipated Doppler frequencies, The data processor 52 combines the aforementioned ~ timing u~i~ 86 and the channel combiner 100, and further includes a pair o ~ilters 102 and a pair of ~ignal samplers 104 connected to output channel~ of the combiner 100. Also included within the data processor 52 are a storage unit 106, a correlator 108, a Fourier transformer 110 and a di criminator 112. The ~amplers 104~ the skorage unit 106 and the correlator 108 are operated by clock signals of a clock (not shown~ within the timing unit 86.
In operation9 the combiner 100 sums together the quadrant signals of the right and the left sides of the detector 96 and outputs their di~ference a~ the output x channel signal. Similarly, the combiner 100 su~s together the signals of the upper and lower quadrants of the detector 96, and outputs their difference as the y channel signal.
The filters 102 filter the a~and y ou~put signal of the comblner 100, the filters 102 being band-pas~ filters which limit the spectrum of the received signals to the band of interest, thereby improving the signal-to-noise ratio. The samplers 104 provide digital sampling of the x and y channel signals from the filters 102, the digital samples being stored in sections 114 of the memory 106.
Ag portrayed in a graph 116 in the.block of the correlator 108, a sucoession of samples of the Doppler ~hifted ~ignal ls taken by each of the samplers 104. These sample~ ~re then correlated agains~ themselves, an ~z~s2a3 autocorrela~ion by ~he correlator 108 to produce an output correlation function containing the desired wind speed data.
The correlation may be done separately for the x and the y channel~, and may al50 be done a~ a cross correlation be ween the x and the y channels.
The extraction of Doppler data by means of the correlation operation i~ de cribed in the article ~Measuremenk of Cro~ Wind Velocity~ by F. Durst et al, Applied Optics, Vol. ~1, No. 14, July lSr 1982~ page~ 2596-2607.
The spectral components of the correlation functions are obtained by the transformer 110 which may be implemented as a well-known fast-Fourier transformation. An amplitude discriminator 112 selects the frequency components having the largest amplitudes as being representative of the wind speed. The amplitude of the wind speed appears as an output signal of the discriminator 112 on the line 64 to be applied to the circuitry 54 (Fig. 1) for calculation of the tip speed ratio.
In the selection of sample~ for the correlation, it may be desirable to u~e only those amples appearing within a preselected time interval after the transmis~ion of a pulse o~ laser light. Such a gelection of 3amples provides the function of range gating for mea~urement of wind cpeed - ~4L5Z~ ~
at a pre~elected range ~rom the propeller 28. As a practical ma~ter, in 'che implementation of the data proces or 52, the function3 of the correlator 108, the transmitter 110, and the descriminator 112 can readily be attained by use of a microprocessor which is suitably programmed to provide the fore~oing functions.
~ umerous programs for correlation, Fourier transformation and selection of signal~ based on amplitude are available for use with commercially available 10 mlcroprocessorY.
By means of the foregoing system, the loadiny of a wind operated electrical generator can be altered in accordance with infor~ation of future wind speed, the information being obtained before a gust of wind reaches the propeller of a wind machine. Such alteration of the loading of the generator, and thus of the propeller itself, permits adjustment of the tip speed ratio of the propeller blades so as to operate the wind machine efficiently by adapting the speed of the propeller to match the wind speed. Thereby, there i~ a more efficient conversion of wind energy to electrical energy.
The use of electro-op~ic Doppler measurement technique~ of a volume of air upwind of the wind machine, in combination with data processing of received Doppler -~ ~ 4 slgnal echoes permit~ a rapid measurement o the wind speed.
~he rapidity of measurement permits adjustment sf the electrlcal loading to be accompli~hed before any wind gu~t reache~ the propeller. Al~o the employment of electro-optic scanning of the la~er beam permits the gathering of data over a much larger area of space than can be obtained by mechanical anemometers.
The foregoing 1~ considered as illustrative only of the principles of the invention. ~urther, since numerouq modi~lcations and change~ will readily occur to ~ho~e skilled in the art, it i5 not desirable to limit the invention to the exact construction and operation shown and de3cribed, and accordingly all suitable modifications and equivalents may be resorted to falling within the scope o the invention as defined by the claims which follow.
.......
Claims (16)
1. A wind energy conversion system comprising a propeller rotatable by force of wind, a generator of electricity mechanically coupled to said propeller for converting power of the wind to electric power for use by an electric load, means coupled between said generator and the electric load for varying the electric power drawn by the electric load to alter the electric loading of said generator, means for electro-optically sensing the speed of the wind at a locution upwind from said propeller and means coupled between said sensing means and said power varying means for operating said power varying means to adjust the electric load of said generator in accordance with a sensed value of wind speed to thereby obtain a desired ratio of wind speed to the speed of a tip of a blade of said propeller.
2. The system as claimed in claim 1, wherein said sensing means comprises a laser for transmission of a beam of light upwind of said propeller, a receiver of laser light reflected from aerosols in a region of space upwind of said propeller and means for scanning a beam of the laser light through said region of space for gathering wind data throughout said region of space.
3. The system as claimed in claim 2, wherein said scanning means comprises an acousto-optic cell providing electronic scanning of the laser beam over a predetermined region of space.
4. The system as claimed in claim 2, wherein said sensing means comprises data processing means coupled between said receiver and said scanning means and including means for correlating a succession of echoes with each other to obtain wind data.
5. The system as claimed in claim 4, wherein said data processing means further comprises means for spectrally analyzing correlation functions of Doppler return signals provided by said correlating means.
6. The system as claimed in claim 2, wherein said sensing means includes data processing means coupled between said receiver and said scanning means for extraction of wind data from received optical signals, said data processing means including means for storing samples of return signals, and a microprocessor for calculating instantaneous velocity of aerosols suspended in the air upwind of said propeller.
7. The system as claimed in claim 6, wherein said operating means include means for sensing a speed of rotation of said propeller and means coupled to said propeller-speed sensing means and to an output terminal of said data processing means for calculating a ratio of wind speed to the speed of the tip of a blade of said propeller.
8. The system as claimed in claim 2, wherein said receiver of laser light includes a four quadrant detector and a lens assembly for eliminating atmospherically induced effects of beam wander.
9. A wind energy conversion system comprising a propeller rotatable by a force of wind, a generator of electricity mechanically coupled to said propeller for converting power of said wind to electric power for use by an electric load, means coupled between said generator and the electric load for varying a duty cycle of electric power coupled from said generator to the electric load to thereby alter the loading of the generator and the propeller by the electric load, means for transmitting a laser beam upwind of said propeller to gather wind speed data from a predetermined region of space, means for receiving laser light reflected from aerosols carried by air in said predetermined region of space, data processing means coupled between said transmitting means and said receiving means for extracting wind data from received echoes of light impinging upon said receiving means and means coupled between said data processing means and said power varying means for operating said power varying means to adjust an electric loading of said generator in accordance with wind speed data to thereby attain a desired ratio of wind speed to the speed of the tip of a blade of said propeller.
10. The system as claimed in claim 9, wherein said operating means includes means for sensing a speed of rotation of said propeller, and means coupled to an output terminal of said data processing means for forming a ratio of wind speed provided by said data processing means to the tangential speed of a tip of a blade of said propeller.
11. The system as claimed in claim 10, wherein said operating means further comprises means for comparing the speed ratio provided by said ratio forming means to a reference ratio value to thereby conform an actual ratio of speed to a desired ratio of wind speed to blade tip speed.
12. The system as claimed in claim 11, wherein said transmitting means includes means for pulsing a laser beam, and means for electronically scanning a laser beam through said predetermined region of space.
13. The system as claimed in claim 12, wherein said data processing means include means for sampling optical echoes reflected from aerosols in said predetermined region of space, means for storing a succession of samples of the echoes, and means for correlating stored samples of the echoes with each other to extract wind data.
14. The system as claimed in claim 13, wherein said receiving means includes a filter for attenuating a transmission frequency of light transmitted by said transmitting means.
15. The system as claimed in claim 14, further comprising timing means for synchronizing an operation of said transmitting means and an operation of said receiving means with an operation of said data processing means to thereby associate wind speed data with specific locations in said predetermined region of space.
16. The system as claimed in claim 9, wherein said means for receiving laser light includes a four quadrant detector and a lens assembly for eliminating atmospherically induced effects of beam wander.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000519779A CA1245283A (en) | 1986-10-03 | 1986-10-03 | Wind energy conversion system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000519779A CA1245283A (en) | 1986-10-03 | 1986-10-03 | Wind energy conversion system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1245283A true CA1245283A (en) | 1988-11-22 |
Family
ID=4134095
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000519779A Expired CA1245283A (en) | 1986-10-03 | 1986-10-03 | Wind energy conversion system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1245283A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2995810A1 (en) | 2014-09-10 | 2016-03-16 | Acciona Windpower, S.A. | Control method for a wind turbine |
-
1986
- 1986-10-03 CA CA000519779A patent/CA1245283A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2995810A1 (en) | 2014-09-10 | 2016-03-16 | Acciona Windpower, S.A. | Control method for a wind turbine |
| US10094360B2 (en) | 2014-09-10 | 2018-10-09 | Acciona Windpower, S.A. | Control method for a wind turbine |
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