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EE 499-002 WIND POWER #2 WECS FUNDAMENTALS

Dr. Venkata Yaramasu Assistant Professor of Electrical Engineering Director of Advanced Motors, Power Electronics, and Renewable Energy (AMPERE) Laboratory School of Informatics, Computing, and Cyber Systems (SICCS) Northern Arizona University Phone: +1-928-523-6092 E-Mail: [email protected]

Office Hours: MoWeFr 12.30-1.30 p.m. in #69-210 By appointment in #90-112

Lecture: MoWe 11.30 a.m. to 12.20 p.m. in #69-224 Lab: Friday 11.30 a.m. to 2.00 p.m. in #69-234

Slides Credit: Dr. Bin Wu, Ryerson University, Canada.

Spring 2017 Ultrasonic Anemometer (Clipperwind)

Topics

1. Wind Turbine Components

2. Wind Turbine Aerodynamics

3. Modeling of Turbines

4. Maximum Power Point Tracking (MPPT)

1. Wind Turbine Components Fixed Speed Turbine Components

Photo courtesy: Bosch Rexroth AG

1. Wind Turbine Components Variable Speed Turbine Components

 Mechanical Components (Tower, Blades, Nacelle, Rotor Hub, Gearbox,

Pitch Drives, Yaw Drives, Brakes)

 Electrical Components (Generator, Converter, Transformer, Cables)

 Control Systems

Photo courtesy: Bosch Rexroth AG

1. Wind Turbine Components WT Components in Motion

https://www.youtube.com/watch?v=W7ZHB9VS2b8

1. Wind Turbine Components Turbine Blades

pwM CvAP 3

2 1 

Mechanical power captured by the blade:

ρ ‐ air density [kg/m3] A ‐ swept area [m2] vw ‐ wind speed [m/sec] Cp ‐ power coefficient of the blade

Direction of rotation

[W]

1. Wind Turbine Components Turbine Blades

 Mechanical power PT extracted from the wind kinetic power Pw is:

pwpwM CvACPP 3

2 1  W

 Cp = power coefficient of blades. Maximum value is __________.

Practical values are between ________ and _________.

 ρ = air density (kg/m3). Air density is a function of altitude,

temperature, and humidity. At sea level and at 15◦C,

air has a typical density of 1.225 kg/m3.

 A = rotor swept area (m2) =

 rT = blade radius (m)

 vw = wind-speed velocity (m/s).

1. Wind Turbine Components Turbine Blades

Question: How to capture more power from the wind?

Answer:

1. 2.

3. 4.

Example: ρ = 1.225 kg/m3, rT = 43.36 m, vw = 12 m/s, and Cp = 0.48.

Calculate PT.

Solution: pwT CvAP 3

2 1  W

Question: Can a 3MW WT be used to generate 4MW power

during high wind speed?

Answer:

1. Wind Turbine Components Turbine Blades

Question: What are the typical values for cut-in, rated and cut-out speeds?

Answer:

Question: Why PT curve is flat from rated to cut-out wind speed?

Answer:

1. Wind Turbine Components Pitch Drives

Photo courtesy: Bosch Rexroth AG

Pitch drives

Question: What is the purpose of pitch control ?

Answer:

Question: What are other power regulation methods ?

Answer:

1. Wind Turbine Components Pitch Drives

https://www.youtube.com/watch?v=TMbt3ca0XXg

1. Wind Turbine Components Yaw Drive

Yaw gear and bearing

Yaw motor drives

Tower conector ring

Yaw motor drives

Nacelle frame

Planetary gear

Yaw brakes Photo courtesy: Nordex

Purpose of yaw drive:

To turn the turbine rotor (blades) into the wind

1. Wind Turbine Components Gearbox

Photo courtesy: GE

Drivetrain Technologies

Purpose:

To adapt the low speed of the WT rotor to the high speed of the generator.

1. Wind Turbine Components Mechanical Brakes

Photo courtesy: HANNING & KAHL

Question: Why the mechanical brake is mounted on the high-speed shaft ?

Answer:

1. Wind Turbine Components Wind Sensor (Anemometer)

Question: What are different types of anemometers ?

Answer:

Photo courtesy: Clipperwind

1. Wind Turbine Components Wind Generators

Question: What is the oldest type of wind generator ?

Answer:

1. Wind Turbine Components Wind Generators

SCIG Photo courtesy: ABB Photo courtesy: ABB

Photo courtesy: Wikov

Photo courtesy: ABB

DFIG PMSG Low Pole

WRSG

Photo courtesy: Enercon

WRSG High Pole

Photo courtesy: Windtec-AMSC

HTS-SG

1. Wind Turbine Components Wind Generators

1. Wind Turbine Components Other

Other major components in WT are:

 Power converter (low voltage and medium voltage)

 Power transformer

 Power cables

 Mechanical control systems

 Electrical control systems (digital control systems)

Question: Calculate line current of 5 MW WT with 690 V and 3000 V?

Answer:

2. Wind Turbine Aerodynamics Power Characteristics

vw (m/s)

Rated power

Cut-in Rated Cut-out

Theoretical power curve

Min. power

Parking mode

Operating region

Practical power curve

Stall or pitch control

Generator control

Q: What are the typical values for cut‐in, rated and cut‐out speeds? A:

2. Wind Turbine Aerodynamics Passive Stall Control

 Simplest method among the group: no need for motor drives and electronic control

 The rotor blades are firmly fixed (bolted) to the rotor hub at a fixed angle

 At higher wind speeds, the turbulence created on rotor surface causes airfoils to

lose lift force, thereby output power decreases

 As wind speed increases above the rated value, output power decreases gradually,

thus leading to low conversion efficiency

 Used in low-power to medium-power WTs

2. Wind Turbine Aerodynamics Active Stall Control

Stalling angle of attack

Strong wind flow (vw > rated)

Fw,stallFull stall Fw,rated

Rated wind flow

Rated angle of attack

(a) At rated wind speed (b) Above rated wind speed

R S

 Advanced version of passive stall control with adjustable rotor blades

 At higher wind speeds, output power is reduced by moving (pitching) the blades

into the wind, thus causing turbulence (stall mechanism) over the blades

 Improves wind energy conversion efficiency at low wind speeds

 Ensures that output power does not exceed the rated value during high-wind-speed

conditions

 Used in medium-power to high-power WTs.

2. Wind Turbine Aerodynamics Stall Comparison

Active stall is more efficient than the passive stall method.

2. Wind Turbine Aerodynamics Pitch Control

Full pitchStrong wind flow

(vw > rated)

Fw,pitch

Pitched angle of attack P

Fw,rated

Rated wind flow

Rated angle of attack R

(a) at rated wind speed (b) Above rated wind speed

 Rotor blades are adjustable similar to active stall turbines

 Pitch control mechanism is assisted by an electronic controller and motor (or hydraulic) drives

 During high wind speeds, the rotor blades turn along the longitudinal axis (pitching) such that

angle of attack of the blades is reduced

 Active stall method turns the blades “into wind” to create a stall mechanism, whereas pitch

control turns the blades “out of wind”

 Provides faster control actions than the passive stall and active stall controls

 Used in modern high-power WTs

2. Wind Turbine Aerodynamics Full Stall and Full Pitch

Full stall

Photo courtesy: accionsustentable.cl

Full pitch

3. Modeling of Wind Turbines Power Coefficient of WT

i p CeCCC

C CC i 

 

75 2

43 2

 

  

 



= Tip speed ratio (TSR)T

 = Pitch angle (degrees)

71 CC  = Turbine constants

= Intermittent TSR i

pwM CvAP 3

2 1  [W]Turbine Mechanical Power:

Power Coefficient:

3. Modeling of Wind Turbines Tip Speed Ratio (TSR)

TM T v

r   ωM – mechanical speed of the turbine (blades)

rT – radius of the turbine rotor (blade length) vw – wind speed

Tλ

pwM CvAP 3

2 1 

 Mp PC

Rated R

attack of angle R

Relationship between the Power Coefficient and Tip Speed Ratio

Blade tip speed

3. Modeling of Wind Turbines Optimal Tip Speed Ratio (OTSR)

TRM

TRM optT

v rn

v r

, ,

)60/2(  

 



 

Optimal tip speed ratio (for variable speed operation):

0 2 4 6 8 0

0.1

0.2

0.3

0.4

10 12 14 16

Cpmax Cp

Rated R

Tλ

λT,opt

= Turbine speed in rpm Mn

= Rated turbine speed in rpm RMn ,

= Turbine mechanical speed (rad/sec) M

= Rated turbine speed (rad/sec) RM ,

= Rated wind speed (m/s) Rwv ,

3. Modeling of Wind Turbines Cp versus TSR

0 1

0.1

0.2

0.3

0.4 max,pC

o0

o5

o10

optT , T

Cp versus TSR with Pitch Angle β as a Parameter

Pitch angle β: The pitch angle is defined as zero (β= 0) when a turbine operates at the rated conditions with the optimal TSR.

3. Modeling of Wind Turbines Cp versus TSR

0.1

0.2

0.3

0.4 max,pC

o0

0 2 4 6 8 10 T

optT ,

0.1

0.2

0.3

The pitch angle is kept at zero when the wind speed is below its rated value such that the turbine can harvest the maximum power from the wind.

Cp versus TSR – Optimal tip speed ratio

3. Modeling of Wind Turbines Intermittent Tip Speed Ratio

)(N.m M

M M

P T

 

The output mechanical torque of the wind turbine

1 035.0

08.0 11

3  

 

 Ti

Intermittent Tip Speed Ratio

)(N.m gbM

m m r

PP T

 

The generator mechanical input torque

iλ

3. Modeling of Wind Turbines Gear Ratio and Mechanical Speeds

Gear ratio

Rm gb n

n r

, = Rated generator speed (rpm) Rmn ,

)rad/sec( ,

woptT M r

v  



Turbine mechanical speed

for variable speed operation

= Rated turbine speed (rpm) RMn ,

Generator mechanical speed )rad/sec(gbMm r 

for fixed speed operation: the turbine speed is almost fixed by the generator

)rad/sec(,RMM  

3. Modeling of Wind Turbines Example 1

Given: Wind turbine parameters

Parameter Value Rated turbine mechanical output power, PM,R 2.3339 MW Rated generator mech input torque, Tm,R 14740 N.m Air density, ρ 1.225 Kg.m3

Turbine rotor radius, rT 46.5 m Rated turbine speed, nM,R 16 rpm Rated wind speed, vw,R 12 m/s Pitch angle, β 0° (zero degree at the rated output)

Turbine constants, [C1 C2 C3 C4 C5 C6 C7] [0.7029, 116.055, 0.4, 0, 8.6614, 21.5, 0.00684]

Rated generator output power, Ps,R 2.3 MW Rated generator speed, nm,R 1512 rpm Wind speed 12 m/s

3. Modeling of Wind Turbines Example 1

Optimal TSR of wind turbine: Solution:

4926.6 12

5.46)60/2(16)60/2(

, , 

 

 

TRM optT v

Intermittent TSR of wind turbine:

4019.8 1

10 035.0

04926.6 1

1 035.0

08.0 11

3  

 

 

 

 Ti 4019.8 i

Find: • The optimal and intermittent tip speed ratio, • The power coefficient of wind turbine, • The mechanical speed of turbine and gear ratio, and • The turbine output power and generator mechanical input torque.

3. Modeling of Wind Turbines Example 1

Solution (Continued)

The power coefficient of wind turbine:

3246.075 2

43 2

 

  

 



i p CeCCC

C CC i 

 

The mechanical speed of turbine:

rad/sec6755.1 5.46

124926.6, 

 

woptT M r

v 

The gear ratio:

5.94 16

1512

, 

Rm gb n

n r

3. Modeling of Wind Turbines Example 1

Solution (Continued)

The turbine output mechanical power:

The generator mechanical input torque:

W103339.23246.0125.46225.1 2 1

2 1 6323   pwM CAvP

N.m14740 5.946755.1

103339.2 6 

 

 

 gbM

M m r

P T



(rated)

3. Modeling of Wind Turbines Example 2

Given: Wind turbine parameters for DD PMSG

Parameter Value Rated turbine mechanical output power, PM,R 3.0 MW Rated generator mech input torque, Tm,R 1273 kN.m Air density, ρ 1.225 Kg.m3

Turbine rotor radius, rT 43.3553 m Rated turbine speed, nM,R 22.5 rpm Rated wind speed, vw,R 12 m/s Pitch angle, β 0° (zero degree at the rated output)

Turbine constants, [C1 C2 C3 C4 C5 C6 C7] [0.3915, 116, 0.4, 0, 0.5, 21, 0.0192]

Rated generator output power, Ps,R 2.964 MW Rated generator speed, nm,R 22.5 rpm Wind speed Above 12 m/s

3. Modeling of Wind Turbines Example 2: Effect of Pitch Angle on Power Output

4. Maximum Power Point Tracking Turbine Power-Speed Characteristics

PM – mechanical power of wind turbine ωM – mechanical speed of wind turbine

For a given wind turbine, the curves are fixed at a given wind speed.

4. Maximum Power Point Tracking Fixed Speed WT

Turbine/generator operates at the rated speed (1pu).

4. Maximum Power Point Tracking Turbine Power-Speed Characteristics

3)( MMP 

3 MMP With MPPT,

MMM TP From

2 MMT we have

Turbine (generator) speed is adjusted such that it operates at the maximum power point.

4. Maximum Power Point Tracking Comparison of Fixed-Speed and Variable-Speed WTs

For a given wind speed (lower than the rated), the variable speed operation produces more power.

Note: Wind turbines operate below the rated speed most of the time.

4. Maximum Power Point Tracking MPPT 1: Optimal TSR (OTSR) Control

Key Points:

• Wind speed is measured.

• wm* (reference) is

provided according to wind

speed.

• Requires WT parameters

• Very widely used in WECS.

4. Maximum Power Point Tracking MPPT 2: WT Power Curves (WTPC)-Based Control

Key Points:

• Wind speed is measured. • Ps* (reference) is provided according to wind speed.

4. Maximum Power Point Tracking MPPT 3: Optimal Torque (OT) Control

4. Maximum Power Point Tracking MPPT 4: Power Signal Feedback (PSF) Control

Key Points:

• Rotor speed is measured. • Ps* (reference) is provided according to rotor speed.

4. Maximum Power Point Tracking Comparison of MPPT Control Techniques

OTSR is very widely used in WT industry.