aerodynamics of wind turbine control systems by chawin chantharasenawong 21 august 2009
TRANSCRIPT
Aerodynamics of Wind Turbine Control Systems
By Chawin Chantharasenawong
21 August 2009
Chawin Chantharasenawong ชวิ�น จั�นทรเสนาวิงศ์�
Academic staff at
Department of Mechanical Engineering
King Mongkut’s University of Technology Thonburi (KMUTT)
มหาวิ�ทยาลั�ยเทคโนโลัย�พระจัอมเกลั�าธนบุ�ร�
Our work with wind energy
Today’s topic Large wind turbines Types of wind turbines Turbine blades Types of power controls
How they work? Pros and cons
Conclusions
Large wind turbines Large wind turbines are wind turbines with
rated power over 1MW
Wind turbines are typically classified into Horizontal axis wind turbines (HAWTs) Vertical axis wind turbines (VAWTs)
Horizontal Axis Wind Turbines
Vertical Axis Wind Turbine
Advantages of large HAWTs and VAWTsHAWTs
Due to the atmospheric boundary layer, wind speeds are usually higher with altitude. The power available is proportional to the wind seed to the power of three.
VAWTs Easy maintenance as
it is close to ground Wind direction does
not affect the power production
No high tower required, hence lower initial cost
32
2
1vrP
Disadvantages of large HAWTs and VAWTs
HAWTs Large modern wind
turbines consist of over 90m high towers and 40m long blades. Transportation is difficult and costly.
Dangers to birds in the vicinity
VAWTs Lower efficiency when
compared to an equivalent HAWT because part of the VAWT is always turning against the wind without producing power
VAWTs cannot be installed on a high tower to take advantage of the high speed wind due to vibration problems
The turbine must be dismantled for maintenance
Optimum number of blades For optimum number of blades we need to
consider
B : number of blades CL/CD : aerofoil characteristics Lambda : tip speed ratio
BCC
B
C
d
lp
21
57.0208
32.1
27
16 2
1
3
2
2
max,
Efficiency
Optimum number of blades
* Calculation of Cp max is performed using information from ‘Wind Energy Explained’ by Manwell et al. and Wilson et al. (1976)
BC
CB
C
d
lp
21
57.0208
32.1
27
16 2
1
3
2
2
max,
1 blade
More blades
Optimum number of blades
Optimum number of blades
Number of blades
Power coefficient
Improvement
1 0.467 -2 0.507 8.57%3 0.525 3.55%4 0.536 2.10%5 0.543 1.31%6 0.548 0.92%7 0.552 0.73%
Consider a wind turbine operating at tip speed ratio = 5.
0 1 2 3 4 5 6 7 80.42
0.44
0.46
0.48
0.5
0.52
0.54
0.56
Number of blades
Pow
er
coeffi
cie
nt
Efficiency of blade section
Blade section characteristics Preference
High lift to produce torque Low drag to prevent flapwise
damages and reduce losses Aerofoil shape is the most
suitable, ie. high lift-to-drag ratio
maxDrag
Lift
BCC
B
C
d
lp
21
57.0208
32.1
27
16 2
1
3
2
2
max,
Preliminary Conclusion
Modern megawatt class wind turbines are almost exclusively equipped with three wing-shaped rotor blades mounted on a horizontal axis.
Wind turbine operation
Cut-in Rated
Cut-out
* Actual power curve of CPC NEWUNITE FD-77-1500-III 1.5MW wind turbine which has been installed at Huasai, Nakonsrithammarat
Excess energy
2 4 6 8 10 12 14 16 18 20 220
1000
2000
3000
4000
5000
6000
Wind turbine power curveAvailable wind power (Efficiency = 0.587)
Wind speed (m/s)
kilow
att
s
Calculated with air density = 1.225 kg/m3
Excess energy
Power control In case of stronger winds it is necessary to
waste part of the excess energy of the wind in order to avoid damaging the wind turbine. All wind turbines are therefore designed with some sort of power control.
There are two different ways of doing this safely on modern wind turbines. Stall control Pitch control
Stall controlled wind turbine
Rotor blades are fixed to the hub on a stall control wind turbine
No mechanisms, no moving parts
How does stall control work?
Local angle of attack is a function of wind speed, ie. High wind speed = high
angle of attack
How does stall control work?
Angle of attack
Lift
coeffi
cient
Stall controlled wind turbine
operation conditions during high wind speeds
How does stall control work? High wind speed High angle of attack Flow separation over upper surface Stall Lift force is broken Rotor torque is reduced Power is controlled
Pitch controlled wind turbine
Electronic controller monitors the wind turbine power output
When the power exceeds the limit, it sends a signal to the blade pitch mechanism to turn the blade.
Reduce local angle of attack
How does pitch control work?
Angle of attack
Lift
coeffi
cient
Pitch controlled wind turbine
operation conditions during high wind speeds
Advantages and disadvantages
Aerofoil is most efficient (maximum lift-to-drag ratio) when operating at its designed angle of attack, which is usually below the stall angle
Pitch controlled turbines operate below the stall angle during high wind speeds
Drag
Lift
maxDrag
Lift
Advantages and disadvantages
Aerofoils entering stall are associated with formation of leading edge vortices, which cause large changes in aerodynamic forces leading to strong structural vibration and ultimately reducing fatigue life
Pitch controlled turbines are designed to operate below stall angles at all times
Advantages and disadvantages
• Stall controlled turbines are safer during sudden changes in angle of attack Gusts Wind shear
Angle of attack
Lift
coeffi
cien
t
Advantages and disadvantages
Almost all modern large wind turbines are equipped with pitch control systems, hence its maintenance services and spare parts are readily available.
Moving parts in the pitch mechanism require regular maintenance at a cost
Conclusions Modern multi-megawatts wind turbines are
designed with 3-blade HAWT configurations Pitch control system is favourable Stall control system has several minor
advantages
Thank you for your attention
Chawin Chantharasenawong Mechanical Engineering Department
KMUTT [email protected]
http://DrChawin.com