Lecture 30 November 4, 2013
ECEN 2060
Lecture 30
Fall 2013
Wind Power Systems
• 1. Windmills go back a long time. A key money
maker for milling grain.
• 2. First use for electrical generation in 1891 by Poul
la Cour used generate hydrogen.
• 3. Used shortly afterward in the rural US.
• 4. 1941 Grand Paw’s Knob Vermont 1250 kW,175ft
two blade system. Failed in 1945
• 5. 1970’s to mid 1980’s in California and then to
Europe
ECEN2060
2
Rapid Grow of Wind Capacity
ECEN2060
3
World Wide Growth of Wind Energy
ECEN2060
4
Fraction of Total Generation by Wind
ECEN2060
5
Data on Wind
ECEN2060
6
Types of Wind Turbines
ECEN2060
7
Characteristics of Some Wind Turbines
• 1. Horizontal Axis Wind turbine Up wind and Down
wind.
A. Down wind has advantage of self aligning (yaw)
 B. Disadvantages Shadowing by tower that increases
flexing of the blades which, decrease power, increases
fatigue and noise.
 C. Up wind Advantage More power, Smoother
 D. Disadvantages more complicated control

• 2. Vertical Axis, Darrieus
• Advantage Heavy equipment on the ground. Lighter tower.
• Disadvantage Blades close to the ground where the wind is
slower. Low starting torques. Hard to feather in high winds.
ECEN2060
8
Schematic for Horizontal Wind
ECEN2060
9
Wind Turbine Gear Box
ECEN2060
10
Area of Capture
ECEN2060
11
Wind Turbines
• Most wind turbines are up wind horizontal.
• Many blades high torque and works well at low
wind speeds.
• Two blades turn faster than 3 blades, less
turbulence. 3 blades smoother and installed the
most. 3 blade weights more.
ECEN2060
12
Pitch Angle Controls Lift, Speed and Power
ECEN2060
13
High Pitch Can Lead to Stall
ECEN2060
14
Wind is Slowed by Blades
•1
ECEN2060
15
Wind Power
ECEN2060
16
Wind Power
ECEN2060
17
Area of Darrieus
ECEN2060
18
Lecture 31 November 6, 2013
ECEN2060
19
Temperature Correction for Air Density
The molecular weight of air is approximately 28.97 and the density at
15o C is 1.225 kg/m3
ECEN2060
20
Dry Air Pressure at 1Atmosphere
ECEN2060
21
Altitude Correction
ECEN2060
22
Table of Air Pressure with Corrections for
Temperature and Altitude.
•.
ECEN2060
23
Effects of Tower Height
Z is the roughness length
ECEN2060
24
Surface Friction
ECEN2060
25
Roughness
ECEN2060
26
Effects of Height with Different Roughness
ECEN2060
27
Effects of Variation of Wind Speed with
Height on Stress
This leads to vibrations, noise, blade flexing and fatigue. Factors to 1.45 more
power at top to bottom in example.
ECEN2060
28
Maximum Rotor Efficiency
Betz limit 1/3 initial velocity
ECEN2060
29
Blade Efficiency
Assume uniform velocity over the blade
To find the maximum power efficiency
ECEN2060
30
Real Turbines
1 Best 80% of Betz limit more often 40% to 50%
2. Depends on ratio of rotor speed to wind speed. Often defined in terms of
Tip speed.
ECEN2060
31
Blade Efficiency
ECEN2060
32
Efficiency for Different Blade Systems
ECEN2060
33
Idealized Operating Power Curve
ECEN2060
34
Matching Generator Size to Rotor Diameter
with Wind Speed
•1
ECEN2060
35
Blade Speed Limits
• 1. Want to operate in the TSR of 4-6
• 2. Example 40m blades 600kW ,14m/s, This leads
to 26 revolutions per minute and tip speed of 56m/s
• 3. Required gear ratio to get to 1800rpm of 67.4
• 4. Wind Power of 2,112 kW to get 600kW or an
efficiency of 28%
ECEN2060
36
Some Real Turbines
•1
ECEN2060
37
Efficiency and Power for Some Turbines
ECEN2060
38
Average Wind Speed Classifications
ECEN2060
39
Wind Speed Measurements
ECEN2060
40
Types of Generators
• 1. Synchronous Generators


A. Fixed Speed
Rotational speed N(rpm) = 120𝑝 𝑓 p = number of poles
f = frequency for a three phase winding.
2. Induction Generators These generators have slip
between the rotor speed and the speed of the rotating field
in the stator.

ECEN2060
41
Generators for Wind Turbines
• 1. A key issue is the variable of the wind speed and
a need for nearly constant speed to achieve 50
or 60hz.
• 2. Basic equations
• F= q(E + vxB) = qE + I xB and Vinduced = - B  ds = - d ~ I
t
dt
3. Note the current I is proportional to the rate of
change of the magnetic field B and the force is
proportional to the product B ∂B/∂t
3. Synchronous Generators
A. Need for constant speed to keep output at 60hz.
4. Induction Generators
ECEN2060
42
Types of Systems
ECEN2060
43
Synchronous Generator
ECEN2060
44
A Direct Drive Permeate Magnetic Machine
•1
ECEN2060
45
Induction Generator
• 1.Fixed windings on the rotor and does not require
brushes or electrical contact with the rotor.
• 2. The rotor runs a little slower than the rotating
field when operating as a motor and faster
when it is working as a generator.
• 3. The induced current in the rotor conductors
generate the magnetic fields that lead to the
torques.
ECEN2060
46
Forces with a Rotating Magnetic Field
ECEN2060
47
Squirrel Cage Rotor
Note 3 phase driving current gives a rotating field when the currents are
120 degrees out of phase
Synchronous speed Ns = 120 f/p where f is the frequency and p
Is the number of poles.
ECEN2060
48
Squirrel Cage Rotor
ECEN2060
49
Rotating Magnetic Fields
ECEN2060
50
Induction Motor Torque –Slip Curve
ECEN2060
51
Example of Induction Motor.
ECEN2060
52
Inductance Machine as Generator
1. The wind starts the machine as a motor until it gets above synchronous speed
2. Can be connected to the grid or self excited with a capacitor and remnant
magnetic field. Set it to resonate with the Stator Inductance
ECEN2060
53
Need for Speed Control
• 1. Want to operate with a tip speed ratio of 4-6 for
maximum power and blade efficiency Cp
• 2. If direct connection to the grid need a fixed blade
speed for phase and frequency control to match
frequency on the grid if you have a fixed turbine to
generator connection.
• 3. Need to shed power in high winds.
4. Use a gear box.
• 5. Use pitch control of the blades
• 6. Control of slip which in turn controls power.
• 7. Doubly wound rotor.
ECEN2060
54
Inductance Generator Speed Control
ECEN2060
55
Examples of Speed Adjustments.
ECEN2060
56
Control of the Number of Poles in the Stator
• 1. This can be done by changing the connections
on the windings. For example two poles adjacent to
each other can be connected to look like one. This
is 1/2 the frequency for a fixed speed.
• 2. Change gear ratio.
• 3. Varying the resistance seen by the rotor winding
varies the slip.
• 4. Use an indirect connection to the grid by way of
an inverter AC to DC to AC(60hz.) This allows for
variable frequency into the inverter and variable
turbine speed.
ECEN2060
57
Variable Speed Turbine and Indirect
Connection to the Grid
ECEN2060
58
Doubly Wound Induction Machine
ECEN2060
59
Gearless Drive
•1
ECEN2060
60
Average Wind Power
This is the wind turbine owners get paid.
Note there is a big difference between V average and V3average
ECEN2060
61
A wind speed histogram
ECEN2060
62
A Probability Density Function
ECEN2060
63
Weibull and Rayleigh Functions
ECEN2060
64
Weibull Density Functions
ECEN2060
65
The Rayleigh Probability Density Function
ECEN2060
66
Rayleigh Distribution
ECEN2060
67
Some Real Data
ECEN2060
68
Midwest Wind
ECEN2060
69
ECEN2060
70
ECEN2060
71
Wind Turbine Gear Box
ECEN2060
72
ECEN2060
73