ZC-2010_Wind_Power_Shanghai_1

Wind Power Technology (1) Zhe Chen Aalborg University D t t f E T h lDepartment of Energy Technology zch@et.aau.dk htt // t dk 1 http://www.et.aau.dk Contents • Wind Power Technology Basics • Wind Power Generators • Wind Energy Conversion Systems• Wind Energy Conversion Systems 2 Wind Power Conversion System Mechanical power Electrical Power Wind power Power converter (optional) Supply gridRotor Gearbox (optional) Power transformer Generator Power conversion & Power transmission Power conversion & control Power transmission Power conversion & control 3 Wind Power Conversion SystemWind Power Conversion System Vestas V90-1.8 MW & 2.0 MW DFIG wind turbine (Reproduce by kind permission of Vestas A/B) 4 A/B) Power in Wind )(W/m 2 1 23vPwind ρ= 2 Wind speed (m/s) Power in the wind (Watt/m2)(m/s) (Watt/m ) 3 16 6 1306 130 12 1035 5 Wind Speed Distribution • The wind speed distribution describes the probabilities of winddescribes the probabilities of wind speed distribution ¾Gale forces are rare so are very¾Gale forces are rare, so are very light wind speeds ¾Moderate wind speeds are more¾Moderate wind speeds are more common • Area under curve equals to 1q 6 Wi d S d Di t ib ti E lWind Speed Distribution Example • In this example, the most often occurring wind speed is 5.5 m/s • 6.6 m/s is the median of the distribution (the median halves the blue i 50% f i i d d i b 50% i ’ b l )area, i.e. 50% of time wind speed is above, 50% it’s below) • 7 m/s is the average wind speed (multiplying each wind speed with its probability and adding them up leads to the mean wind speed)its probability and adding them up leads to the mean wind speed) ∫∞ )( dVfVV ∫ ⋅⋅= 0 )( dVufVVmean 7 Weibull Distribution • Wind distribution may be approximated by applying the Weibull di t ib tidistribution • The Weibull distribution defines a distribution of wind speeds by usingThe Weibull distribution defines a distribution of wind speeds by using 2 parameters ¾ Scale parameter A ¾ Shape parameter k 8 Weibull Distribution kvkk ⎟⎞⎜⎛−⎞⎛ 1 Weibull probability density function: Cumulative distribution: kv ⎟⎞⎜⎛ Ae A v A kvp ⎟⎠⎜⎝−⋅⎟⎠ ⎞⎜⎝ ⎛⋅=)( AevF ⎟⎠⎜⎝ −−=1)( Weibull Distribution 1 0.14 0 6 0.7 0.8 0.9 0.1 0.12 0.3 0.4 0.5 0.6 0.04 0.06 0.08 cumulative relative 0 0.1 0.2 0 5 10 15 20 25 0 0.02 9 0 5 10 15 20 25 wind speed [m/s] Distribution of Wind and EnergyDistribution of Wind and Energy • Energy normalised with annual energy production • Example wind distribution:Example wind distribution: ¾ A = 7 ¾ k = 2 Wind and Energy Distribution 0.12 0.14 0.14 0.16 0.08 0.1 0 08 0.1 0.12 relative 0.04 0.06 0.04 0.06 0.08 energy 0 0.02 0 5 10 15 20 25 0 0.02 10 wind speed [m/s] From Power Density to Power Output The area under the grey curve gives the g y g amount of wind power per square metre wind flow. In this case a mean wind speed of 7 m/s and a Weibull k=2 The area under the blue curve shows how much of the wind power can be theoretically converted to mechanical power. The total area under the red curve shows how much electrical t i i d t bi ill d t thi it 11 power a certain wind turbine will produce at this site. Th C t I Wi d S dThe Cut In Wind Speed Usually, wind turbines are designed to start running at wind y, g g speeds around 3 to 5 m/s. This is called the cut in wind speed. The blue area to the left shows the small amount of power lost due to h i dthe cuts in speed. The Cut Out Wind Speed The wind turbine will be stopped at high wind speeds above, say 25 m/s, in order to avoid damaging the turbine. The stop wind speed is called the cut out wind speed. The tiny blue area to the right represents that loss of power. 12 Betz' Law Betz' law says that one can only convert less than 16/27 (or 59%) of the kinetic energy in the wind to mechanical energy59%) of the kinetic energy in the wind to mechanical energy using a wind turbine. Betz' law was first from the German Physicist Albert Betz in 1919. 13 Blade Element ModelBlade Element Model Expression of developed torque, captured power and axial thrust force of the turbine. 14Forces on a blade element Blade Element ModelBlade Element Model Th lif d d f i l h llThe lift and drag forces per unit length are generally expressed in terms of the lift and drag coefficients CL and )( 2 2 αρ LrelL CVcf = CD . )( )( 2 2 αρ l LrelL CVcf f = )( 2 αDrelD CVf = c is the chord length of the blade element and α incidence anglec is the chord length of the blade element , and α incidence angle βφα −= 15 βφ Blade Element Model Typical lift and drag coefficients of an aerofoil h lif f d l f l h h d iThe lift force develops useful torque whereas the drag opposes it. A high ratio CL/CD is desirable to achieve high conversion efficiency During stall an abrupt drop of this ratio takes place 16 efficiency. During stall, an abrupt drop of this ratio takes place. Power curve - Aerodynamic ¾Power to the generator- shaft is given by:g g y = ratio between tip-speed and wind speed 17 Force, Torque and Power Typical variations of CQ and CP for a fixed pitch wind turbine 18 F T d PForce, Torque and Power Torque and power vs. rotor speed with wind speed as parameters and β=0 19 F T d PForce, Torque and Power Torque and power vs. rotor speed with pitch angle as parameter and V=12 m/s 20 Force, Torque and Power Power coefficients, CP, of different wind rotor designs 21 Force Torque and PowerForce, Torque and Power Torque coefficients, CQ , of different wind rotor designs 22 RoughnessRoughness Roughness Roughness Energy Landscape Type Class Length (m) Index (%) 0 0.0002 100 Water surface 0.5 0.0024 73 Completely open terrain with a smooth surface, e.g. concrete i i t d trunways in airports, mowed grass, etc. 1 0.03 52 Open agricultural area without fences and hedgerows and very scattered buildings. Only softly rounded hills 1 5 0 055 45 Agricultural land with some houses and 8 metre tall sheltering1.5 0.055 45 Agricultural land with some houses and 8 metre tall sheltering hedgerows with a distance of approx. 1250 metres 2 0.1 39 Agricultural land with some houses and 8 metre tall sheltering hedgerows with a distance of approx. 500 metres 2.5 0.2 31 Agricultural land with many houses, shrubs and plants, or 8 metre tall sheltering hedgerows with a distance of approx. 250 meters 3 0.4 24 Villages, small towns, agricultural land with many or tall sheltering h d f d h d ihedgerows, forests and very rough and uneven terrain 3.5 0.8 18 Larger cities with tall buildings 4 1.6 13 Very large cities with tall buildings and skyscrapers 23 Wind Shear The wind speed at a certain height above ground l l ilevel is: v = vref ln(z/z0 )/ln(zref /z0 ) Where v = wind speed at height z above ground level. vref = reference speed, i.e. a wind speed is already known at height zref .g ref z = height above ground level for the desired velocity, v. z0 = roughness length in the current wind directionz0 roughness length in the current wind direction. z ref = reference height, i.e. the height where the exact wind speed vref is known . Assume the wind speed is 7.7 m/s at 20 m height. If the roughness length is 0.1 m, the wind speed at 60 m height is then vref = 7.7, z = 60, z0 = 0.1, zref = 20 hence, 24 ref , , 0 , ref , v = 7.7 ln(60/0.1) / ln(20/0.1) = 9.2966 m/s Rotor Load Imbalance • Blade loads have a strong azimuth angle dependence • Cause: ¾ Rotational sampling of the uneven wind-field • Deterministic components Tower shadow, wind sheer, • Stochastic components turbulenceturbulence • Concentrated at multiples of rotor speed W0 25 Wind Speed Experienced by the Turbine )cos(ψrhhr −= ⎟⎟ ⎞ ⎜⎜ ⎛ − )cos(ln rh ψ ⎟⎟ ⎞ ⎜⎜ ⎛ ⎟⎟⎠⎜ ⎜ ⎝= 0 ln ln )()( h z hVhV mrm ⎟⎟⎠⎜ ⎜ ⎝ 0 ln z Spatial distribution of the wind passing through the area swept by the turbine 26 Wind Speed Experienced by the TurbineWind Speed Experienced by the Turbine Wind shear Wind shear effect (N=3): (a) Normalised torque fluctuations of each blade 27 and rotor (b) fast Fourier transform of the rotor torque Wind Speed Experienced by the Turbine Tower shadowTower shadow Tower shadow effect (N=3): (a) Normalised rotor torque fluctuations and (b) fast Fourier transform of the rotor torque 28 Wake Effect In fact, there will be a wake behind the turbine, i.e. a long trail of wind which is quite turbulent and slowed down when compared to the winddown, when compared to the wind arriving in front of the turbine. A wind turbine will always cast a wind shade in the downwind direction. Wind turbines in parks are usually spaced from one another in order to avoid too much Wake effect from wind turbine another in order to avoid too much turbulence around the turbines downstream. Picture © Riso National Laboratory, Denmark 29 Wake Effect in Wind Farm 30 Park Effect Typically, the energy loss from the Park Effect will be somewhere around 5 per cent. Turbines in wind parks are usually spaced somewhereusually spaced somewhere between 5 and 9 rotor diameters apart in the prevailing wind direction, and between 3 and 5 diameters apart in the direction perpendicular to the prevailingperpendicular to the prevailing winds. 31 Offshore wind farms Wind farm Nysted Horns Rev Owner DONG Energy (80%) E.On Sweden (20%) DONG Energy (40%) Vattenfall (60%) 57.5( ) ( ) Turbine number 72 80 Turbine Siemens 2.3 MW Vestas 2 MW 56.5 57.0 e ( ° N ) Turbine type Active stall, 2-speed Pitch, variable speed Rotor diam (D) 82.4 m 80 m Hub-height 69 m 70 m 55.5 56.0 L a t i t u d e Horns Rev g Array 8 (E-W) x 9 (N-S) 10 (E-W) x 8 (N-S) Dist. between t bi 10.3 D (E-W) & 5.8 D (N S) 7 D (E-W & N-S) 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 Longitude (° E) 54.5 55.0 Nysted turbines D (N-S) Rated capacity 165.6 MW 160 MW Annual prod. 595 GWh 600 GWh http://earthobservatory.nasa.gov/IOTD/view.php?id=3389 Longitude ( E) Year comm. 2003 2002 Water depth 6-10 m 6-14 m Di t l d 10 k ( l t) 14 20 k 32 Distance land 10 km (closest) 14-20 km R.J. Barthelmie, K. Hansen, S.T. Frandsen, O. Rathmann, G. Schepers K. Rados, W. Schlez, A. Neubert, L.E. Jensen, S. Neckelmann, “Modelling the impact of wakes on power output at Nysted and Horns Rev”, EWEC2009 conference March 2009 Marseille, France Power Control of Wind Turbines Wind turbines are designed to produce the rated power at a d i d d i d ddesigned rated wind speed. In case of stronger winds it is necessary to reduce the input wind power in order to avoid damaging the wind turbine. All p g g wind turbines are therefore designed with some sort of power control. 33 A d i f Wi d T bi St llAerodynamics of Wind Turbines: Stall The lift of the wing will increase as theThe lift of the wing will increase as the wing is tilted backwards. The lift from the low pressure on the upper surface of the wing disappears if the air flow on the upper surface stops sticking to the surface of the wing. This phenomenon is known as stallphenomenon is known as stall. An aircraft wing will stall, if the shape of g , p the wing tapers off too quickly as the air moves along its general direction of imotion. 34 The stall effectThe stall effect Attached flow around a profile Separated flow (stall) around a profile 35 Passive stall with fixed blade pitch Aerodynamic stall at a rotor blade with fixed blade pitch angle at increasing wind velocities and fixed rotor speedat increasing wind velocities and fixed rotor speed 36 Po er Control b Rotor BladePower Control by Rotor Blade P i d dPower output vs. wind speed 37 Pitch Controlled Wind TurbinesPitch Controlled Wind Turbines On a pitch controlled wind turbine when theOn a pitch controlled wind turbine , when the wind speed becomes too high, the blade pitch mechanism pitches (turns around their p ( longitudinal axis) the rotor blades slightly out of the wind. When the wind drops, the blades are turned back into the wind again. The computer will generally pitch the blades aThe computer will generally pitch the blades a few degrees with wind changes in order to keep the rotor blades at the optimum angle forp g maximising output for all wind speeds. The pitch mechanism is usually operated using hydraulics. 38 Active Stall Controlled Wind Turbines The active stall machines have pitchable blades like pitch controlled machines. The machines may be programmed to it h th i bl d i th it di ti f h t it hpitch their blades in the opposite direction from what a pitch controlled machine does. It will increase the angle of attack of the rotor blades in order to make the blades go into a deeperthe rotor blades in order to make the blades go into a deeper stall. 39 Pitch to Stall: Power OptimisationPitch to Stall: Power Optimisation • Fixed rotor speed 1.0 1.2 • Pitch angle theta 0.4 0.6 0.8 P o w e r ( p . u . ) 0.0 0.2 0 5 10 15 20 25 Wind speed [m/s] Cp over theta parameter wind speedCp over theta, parameter wind speed 0.4 0.45 0.5 0.2 0.25 0.3 0.35 C p 4m/s 5m/s 6m/s 8m/s 10m/s 0 0.05 0.1 0.15 11m/s -10 -8 -6 -4 -2 0 2 4 6 8 10 theta [degree] 40 Pitch to Stall: Power Optimisation Cp max, optimal theta, linear theta over wind speed 2 2.5 0.45 0.5 1 1.5 0.35 0.4 theta opt. 0 5 0 0.5 3 4 5 6 7 8 9 10 11 12 13 14 e t a / d e g r e e 0 2 0.25 0.3 C p m a x opt. linear theta opt. C -1.5 -1 -0.5 t h 0.1 0.15 0.2 Cp max. -2.5 -2 0 0.05 v / m/s 41 Pitch to Stall: Power Limitation 0 8 1.0 1.2 ) 0.2 0.4 0.6 0.8 P o w e r ( p . u . ) Power over wind speed 2600 0.0 0.2 0 5 10 15 20 25 Wind speed [m/s] 2200 2400 2600 1800 2000 P o w e r [ k W ] -6.0deg -5.0deg -4.0deg -1.0deg 1200 1400 1600 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 wind speed [m/s] 42 Pitch angle schedulesPitch angle schedules Pitch angle schedules for pitch control and active stall controlPitch angle schedules for pitch control and active stall control 43 Power Control by Rotor Blade Controlling the rotor input power by pitching the blade towards feather or towards stall 44 Power curves of different wind turbinesPower curves of different wind turbines 0.75 1 1 Power [PU] Power [PU] Power [PU]Active Stall control 0.75 1 Stall control Pitch 0.25 0.50 0.25 0.50 0.75 0.25 0.50 0.75 55 1010 1515 2020 2525 3030 Vindhastighed [m/s] Wind speed [m/s] (c) 5 10 15 20 25 30 Wind speed [m/s] (b) Wind speed [m/s] (a) 45 Wind Turbine Yaw Mechanism The wind turbine yaw mechanism turns the wind turbine rotor against the wind. 46 Aerodynamic Braking System: Tip Brakes The primar braking s stem for most modernThe primary braking system for most modern wind turbines is the aerodynamic braking system, which turns the rotor blades about 90system, which turns the rotor blades about 90 degrees along the longitudinal axis (in the case of a pitch controlled turbine or an active stall controlled turbine ), or turns the rotor blade tips 90 degrees (in the case of a stall controlled turbine )turbine ). These systems are usually spring operated, in order to work even in case of electrical powerorder to work even in case of electrical power failure, and they are automatically activated if the hydraulic system in the turbine loses pressure. 47 Mechanical Braking System The mechanical brake is used as a backup system for the aerodynamic b ki d ki b kbraking system, and as a parking brake, once the turbine is stopped in the case of a stall controlled turbineof a stall controlled turbine. Pitch controlled turbines rarely need to y activate the mechanical brake (except for maintenance work), as the rotor h hcannot move very much once the rotor blades are pitched 90 degrees. 48 Individual Pitch Control Collective pitch control:Basic Pitch Control Objectives Li it ti f t t hi h i d d• Limitation of power capture at high wind speed Individual pitch control: Advanced Pitch Control Objectives • Reduction of blade loads• Reduction of blade loads • Limitation of actuator rate 49 Load Reduction- 1P & 2P individual pitch control Rotating loads IPC off IPC: 1P only IPC: 1P & 2P u b M y 350 400 m o f r o t a t i n g h [ . ] 200 250 300 S p e c t r u 50 100 150 Normalised frequency (P) [.] 0 50 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 • Dramatic 1P reduction on shaft bending moment • Further reduction of 2P load if 2P harmonic control is added P. Rhead Individual, etc. “ Pitch Control With Integrated Control Algorithm and Load Measurement Instrumentation” 50 Load Reduction- 1P & 2P individual pitch control IPC off IPC: 1P only IPC: 1P & 2P Non-rotating loads y b e a r i n g 35 40 45 e c t r u m o f y a w b M z [ . ] 20 25 30 S p e 5 10 15 Normalised frequency (P) [.] 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 • Reduction in shaft loads results in reduction of low frequency loads on stationary q y y components • Further addition of 2P harmonic control greatly reduces the fatigue-dominant peak around 3P. P. Rhead Individual, etc. “ Pitch Control With Integrated Control Algorithm and Load Measurement Instrumentation” 51 Wi d T bi GWind Turbine Generators A generator converts mechanical energy to electrical energy. Wind turbine generators have to k ith (thwork with a power source (the wind turbine rotor) which supplies very fluctuatingsupplies very fluctuating mechanical power (torque). 52 G t TGenerator Types • Synchronous types:• Synchronous types: ¾Permanent magnet rotor ¾W d ( ll bl i i )¾Wound rotor (controllable excitation) • Asynchronous types (induction generators): ¾Squirrel cage rotor ¾Wound rotor • Doubly fed (rotor accessed through slip rings) • Variable rotor resistance with or without slip rings (Optislip) 53 Choices of turbine rotor connection Wind turbine concepts Geared drive Direct drive ※Advantages of direct-drive concepts i lifi d d i t i b itti th b Geared-drive Direct-drive • simplified drive train by omitting the gearbox • higher overall efficiency and reliability • increased energy yield and higher availability • lower noise of the drive train ※ Disadvantages • larger diameter of the generatorg g • higher cost ☺ Direct drive wind turbine concepts may be more attractive. Especially, most of the larger 54 machines are intended for offshore use where the trend has been toward very low maintenance designs. Gearbox model - Gear setsGearbox model Gear sets High Speed Gear Set Intermediate Gear Set Planetary Gear Set 55 J. Coultate, Z. Zhang, C. Halse, A. R. Crowther, “ The impact of gearbox housing and planet carrier flexibility on wind turbine gearbox durability””, EWEC2009 conference March 2009 Marseille, France Gearbox – A Well-known Trouble Maker for Wind!Maker for Wind! Courtesy of Richard Dupuis, GasTops Ltd WWEC 2008 56Courtesy of Johan Ribrant et al IEEE Transactions on Energy Conversion, March 2007 WWEC 2008 S. Zhang, “NdFeB Magnet Technology for Low Speed Direct Drive”, EWEC2009 conference March 2009 Marseille, France Synchronous GeneratorsSynchronous Generators Electrically excited synchronous generators for Enercon E40 gearless wind power plants; stator (standing) and salient pole rotor 57 (lying) Advantages of PM machines ƒ high energy yield and light weight ƒ no additional power supply for the magnet field excitation ƒ hi h li bilit ith t li iƒ higher reliability without slip rings ƒ compared to EE machines m a c h i n e A F P M R F P M T F P M 58 Radia