MAXIMUM POWER GENERATION USING WIND POWER PLANTS Prepared by: Nur Bekiroglu Zehra Yumurtacı Bedri Kekezoğlu YILDIZ TECHNICAL UNIVERSITY IGEC-2 INTERNATIONAL

MAXIMUM POWER MAXIMUM POWER GENERATION USING GENERATION USING

WIND POWER PLANTSWIND POWER PLANTS

PrPreepared by: pared by: Nur BekirogluNur BekirogluZehra YumurtacıZehra YumurtacıBedri KekezoğluBedri Kekezoğlu

YILDIZ TECHNICAL UNIVERSITY

IGEC-2INTERNATIONAL GREEN ENERGY

CONFERENCE

IGEC-198

INTRODUCTION



CONFERENCE

Today, due to increasing population and industrialization, in developing countries, energy demand can not be met with existing limited sources; therefore the great difference between energy production and consumption becomes even larger.In that situation, it becomes very important for the country to utilize its own resources with higher efficiency.

On the other hand, when the disadvantages of conventional energy production methods are taken into consideration, the importance of renewable energy sources is significant.

Among the renewable energy sources, wind has a significant importance as it is clean, environment-friendly, and continuous and has relatively lower costs.

IGEC-198

INTRODUCTION



CONFERENCE

A lot of regions in the world have wind powered electricity generation potential.

It is considered that the wind energy potential of the area in between the 50° North and South latitudes is 26000 TWh/year and due to economical and other reasons, 9000 TWh/year capacities is utilizable.

According to the studies conducted, it is concluded that 27% of the terrestrial area of the earth encounters 5,1 m/s of annual average wind speed.

It is calculated that if this potential is employed, 8 MW/km2 production capacities and a 240000 GW installed power will be achieved.

IGEC-198

INTRODUCTION



CONFERENCE

Fig.1. Increase of the installed power values of the wind power plants in the world. (American Wind Energy Association and European Wind Energy Association)

Installed Capacity 1995-2005

010000200003000040000500006000070000

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

years

po

wer

(MW

)

IGEC-198

INTRODUCTION



CONFERENCE

Figure 1 shows the increase of the installed power values of the wind power plants in the world and Table 1 shows distribution of installed power over the countries.

It also shows that world’s wind power potential is high and there are countries that use almost all their potential, as well as there are countries that can not use their potential.

Figure 2 shows the distribution of the installed power over the continents. Table 2 shows the distribution of technical potential in European countries

IGEC-198

INTRODUCTION



CONFERENCE

Fig.2. Distribution of the installed power over the continents (European Wind Energy Association

IGEC-198

INTRODUCTION



CONFERENCE

Table 1. Shares of installed wind power in the world.

(World Wind Energy Association)

Total Capacity MW %

Germany 18,428 31,0

Spain 10,027 16,9

USA 9,149 15,4

India 4,430 7,5

Denmark 3,122 5,3

Italy 1,717 2,9

U.K. 1,353 2,3

China 1,260 2,1

Japan 1,231 2,1

N.L. 1,219 2,1

Total(Top 10) 51,936 87,5

Rest of the world 7,368 12,5

World total 59,322 100IGEC-198

INTRODUCTION



CONFERENCE

Table 2.Technical potential for wind power in Europe countries.

( www.mmoistanbul.org)

Technical potential

Total area1000 km2

Region potential1000 km2

Power(GW)

Energy(TWh/year)

Denmark 43 1720 14 29

Germany 357 1400 12 24

U.K. 244 6840 57 114

Italy 301 4160 35 69

N.L. 41 400 3 7

Spain 505 5160 43 86

Turkey 781 9960 83 166

IGEC-198

INTRODUCTION



CONFERENCE

In order to compete within the electricity market, wind power plants must be able to produce electricity with costs that can be compared to fossil fuel production method costs.

Since wind has no cost itself, all the investment costs in such systems consist of the mechanical and electrical parts.

Parallel to technological development in the area, turbine costs have decreased and produced total energy has increased.

Table 3 shows the estimated variations of costs for years.

IGEC-198

INTRODUCTION



CONFERENCE

Table 3. Wind power technology, past, present and future

(American Wind Energy Association)

Technological position 1980 1990 After 2000

Unit energy cost($/kWh) 0.35 $-0.4 $ 0.05 $-0.07 $ <0.04 $

Unit plant cost ($/kW) 2000 $-3000 $ 500 $-800 $ <500 $

Plant lifetime 5-7 year 20 year 30 year

Load factor 50 %-65 % 95 % >95 %

Power range 50-150 kW 300-1000 kW 500-2000 kW

IGEC-198

INTRODUCTION



CONFERENCE

All the factors that affect wind power turbine design, construction and operation, are in balance with cost component. All the studies consulted nowadays are in order to decrease the wind power costs to 0,024$ levels by the year 2010.

Therefore wind power will be competitive with conventional energy sources. The unit cost of the energy produced by the wind power plants vary according to the wind speed.

It is known that as the wind speed increases, the unit cost of the energy produced decreases. As the applications in the USA are analyzed, the change of unit energy cost with wind speed is as in Fig.3.

In EU countries, these values are calculated as 9,6 cent/kWh for 5 m/s wind speed and 3,4 cent/kWh for 10 m/s (European Wind Energy Association ).

IGEC-198

INTRODUCTION



CONFERENCE

Fig.3. Change of unit energy cost with wind speed (www.awea.org)

Effect of Wind Velocity on Unit Cost

0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,16 8,08 9,32

wind velocity(m/s)

un

it c

ost

(cen

t/kW

h)

IGEC-198

Wind speed data used in this study



CONFERENCE

In this study, the wind speed data of point marked with X in Figure 4, which is Çeşme-Kocadağ, on the Aegean Sea coast of İzmir-Turkey. The data is also given in Table 4.

Fig.4. Location of Kocadağ point

(www.eie.gov.tr)

IGEC-198




CONFERENCE

Table 4. Annual and monthly wind speeds at Kocadağ Point

Location Year Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec

Kocadağ 1994 9,5 7,3 6,7 11,1 8,5

1995 10,1 9,4 9,8 6,4 8,5 4,9 10,7 8,0 6,4 9,2 8,3 11,1

1996 9,1 10,0 9,8 7,2 6,2 9,4 9,9 8,5 6,4 7,3 8,3 10,1

1997 9,2 8,8 10,3 7,8 6,8 6,5 7,5 8,6 9,6 9,6 6,4 10,0

1998 6,8 9,8 9,5 7,4 6,7 7,9 9,3 9,5 7,6 7,6 8,1 10,1

1999 9,5 8,9 7,5 6,5 7,5 7,6 8,3 9,1 6,2 7,2 10,5 9,4

2000 8,8 9,7 8,1 6,3 6,9 9,7 8,1 9,8 7,3 7,9 6,4 9,3

2001 8,5 8,9 8,5 8,5 N/A N/A N/A N/A 6,7 9,0 9,3 10,7

2002 8,0 7,7 8,0 7,0 7,0 8,6 8,6 6,5 7,2 5,3 7,1 N/A

2003 N/A N/A 10,0 7,3 6,5 8,0 8,6 9,7 7,8 9,2 6,9 9,3

2004 9,2 N/A N/A N/A N/A N/A 9,5 7,7 9,1 6,7 N/A N/A

2005 N/A 11,5 7,4 19,9 6,1 7,8 N/A 7,4 6,9 8,2 9,5 9,7

Ave. speed per month 8,8 9,4 8,9 8,4 6,9 7,8 8,9 8,6 7,4 7,8 8,4 9,8

(N/A: Not Available) (www.eie.gov.tr)IGEC-198




CONFERENCE

These values are the data given by Electrical Power Resources Survey and Development Administration-Turkey. The average of these speed values are given in Figure 5.

When the data given in Table 4 is analyzed, the monthly wind speed variation given in Figure 5 is obtained. Then the average speed value is calculated to be 8,4 m/s.

IGEC-198




CONFERENCE

Fig.5. Monthly wind speed variation of Kocadağ Point

IGEC-198

MATHEMATICAL MODEL OF WIND TURBINES



CONFERENCE

The power that can be generated by the turbine is expressed as follows;

: Specific weight of the air (kg/m3)

(W) (1)

R : Turbine radius (m)

v : Wind speed (m/s)

Cp : Power coefficient

Cp is related to the limit speed indicated by , and is maximum at a specific turbine speed under different wind speeds. Therefore, the point that Cp is maximum (Cpmax=0,3-0,5) is the point that the present wind gives maximum power (Muljadi et al., 1999). IGEC-198




CONFERENCE

Tip speed ratio is given as;

Here ; is the angular speed of the shaft. Torque of the wind turbine is given as:

(2)

Here, Ct is torque coefficient and is defined as;

v

ω.Rλ

t23t

t CvRρπ2

1

ω

PM (Nm) (3)

Cp = Ct (4)

IGEC-198




CONFERENCE

For constant pitch angle the variation of power coefficient Cp versus tip speed ratio is given in Fig. 6.

Fig.6. Variation of Cp with .

(Duru, T., et al., 2003)

IGEC-198

MATHEMATICAL MODEL OF THE INDUCTION GENERATOR



CONFERENCE

In wind turbines where the wind speed is constant and under high power, synchronous generators are preferred. However, since wind characteristics are usually variable, the component to generate electrical energy needs to have similar characteristics. Since the induction generators are capable of generation electricity both under constant and variable speeds, squirrel cage induction machines are widely used as generators (Orabi et al., 2004). As the induction machine works as a generator, magnetizing current and the reactive power needed are supplied by the source and convert the mechanical power of the shaft into electrical power to feed the source.

Under constant frequency, working as a generator takes place only over synchronous speed. In order to obtain constant amplitude and frequency, generator output is supported with converter, inverter, filter and rectifier.

IGEC-198




CONFERENCE

Using a frequency controller the asynchronous machine can be used as a generator under every speed.

Induction generators are preferred due to their low costs, simple structures, high efficiency values, and for being safe, without electromagnetic oscillations.

In the case that an induction machine is employed as a generator, efficiency can be obtained at levels up to 82% under full load.A three phase, squirrel cage induction motor, can be used as a self-excited generator with the capacitor group connected to the stator coil ends. Initial speed of the excitation by the capacity depends on the residual magnetism values of the rotor.

IGEC-198




CONFERENCE

The residual magnetism of an induction motor previously worked connected to the network induces an EMF to the stator coils depending on the speed, and current passes through the capacitors (Seyoum et al., 2003). If the capacitors are empty and without any load, voltage increases in relation with the speed and time, capacity and saturation value of the stator metal core. Initial speed is now dependant to residual magnetism but the excitation velocity can be reduced by increasing the capacitor values. Even if the values of the excitation capacitors are increased, after a specific frequency, the voltage starts decreasing. This shows that the iron core has reached saturation. After that value, excitation capacitors behave as a load.

IGEC-198




CONFERENCE

In this study, self-excited, three phases, squirrel cage induction machine is used as a generator driven by the wind turbine shaft. Equivalent circuit of the self-excited induction generators reduced to one phase is given in Figure 7.Fig.7. Equivalent circuit of the induction generators

sI

SR SjX

mjX

IISO

RjX RR

RI

s

s)-(1R R

LoadcjX

IGEC-198




CONFERENCE

RS ; Stator resistance (ohm)

(5)

RR; Rotor resistance

jXR; rotor reactance (ohm)

jXS; stator reactance (ohm)

Rm ; magnetization resistance (ohm)

jXm ; magnetization reactance

jXc ; excitation capacitance

s ; slip, and is defined as:

S

RS

ω

ωωs

IGEC-198




CONFERENCE

S; synchronous angular velocity

R; rotor angular velocity

and since

while the generator is working, slip is negative. Stator voltage expression of a squirrel cage induction machine, is as follows:

SR ω ω

RR,SSSSSSSSS I θMIL dt

dIR

dt

dIRV (V) (6)

VS ; stator voltage

IS ; stator current

LS ; stator inductance

MS,R ; mutual inductance

S ; stator flux

IGEC-198




CONFERENCE

The rotor voltage is defined as

J; being inertia coefficient

; being viscous friction coefficient

IR ; rotor current

LR ; rotor inductance

MS,R ; mutual inductance

S ; stator flux

SS,RRRRRRRR I θMIL dt

dIR

dt

dIR0 (V)

(7)

Motion equation of the mechanical part is described in equation (8)

(Nm) (8) dt

θdα

dt

θdJ

I

I θL

θII

2

1M

2

2

R

SR,S

TR

TS

IGEC-198

CALCULATING MAXIMUM TURBINE POWER UNDER DIFFERENT WIND SPEEDS



CONFERENCE

The value that makes the power expression in Equation (1) maximum is the point that Cp is maximum. This value is calculated to be 0,495 for =7 by using Figure 6.

The air density is 1,2 kg/m3. The turbine radius in this study is selected as 15 m. Using the average wind speeds for Kocadağ given in Table 4, maximum power values are calculated using Eq.1. In this study, bound to shaft speed and under various wind speeds, the variations of the turbine power are obtained.

Under different speeds, maximum power points are determined and Pmax= f () is obtained. That variation shown in Fig. 8, ensures Pt = a 2 where “a” is a constant (Muljadi et al., 2001).

IGEC-198

CALCULATING MAXIMUM TURBINE POWER UNDER DIFFERENT WIND SPEEDS



CONFERENCE

Fig. 8. Turbine power variation bound to the shaft speed under different wind speed values.

IGEC-198

MODELING THE WIND TURBINE-INDUCTION GENERATOR GROUP OF THE DESIGNED SYSTEM



CONFERENCE

The block diagram of the system used for simulation is given in Fig.9.

Fig.9. Block diagram used.

Induction Generator

Turbine Load

Excited capacity

Rotor Speed

Wind

IGEC-198




CONFERENCE

Wind speed: 6,9 m/s

As a result of the simulation conducted using the block diagram given in Figure 9, power curves shown in Figure 10 are obtained. Power variations for each wind speed value are given.

Fig.10. Power variations for different wind speeds

IGEC-198




CONFERENCE

Wind speed: 7,8 m/s

Wind speed: 8,4 m/s

IGEC-198




CONFERENCE

Wind speed: 8,6 m/s

Wind speed: 9,8 m/s

IGEC-198




CONFERENCE

In this study, calculations are conducted according to the monthly wind speed values given by EIE (Electrical Power Resources Survey and Development Administration, Turkey) for İzmir Cesme Kocadağ wind observation station. These speed values are used in a turbine-asynchronous generator simulation prepared on MATLAB software and power values are calculated. Wind turbine radius is assumed to be 15 m. It is known that the power coefficient is maximum at the point that maximum power is obtained.

Therefore, in this study, using Figure 6, maximum power coefficient of 0,495 that corresponds to limit speed value 7, is used.

Theoretical and simulation results show that the selected system is capable of obtaining maximum power under different wind speed values.

IGEC-198




CONFERENCE

Using the software prepared with MATLAB, maximum power for each wind speed value is determined and illustrated with graphics. Under minimum wind speed of 6,9 m/s, the calculated power is 69 kW, simulation results give 70,5 kW power.

Calculated power is 197,7 kW

Under annual average wind speed of 8,4 m/s

Calculated power is 124,5 kW

Simulation results give approximately 120 kW

Under maximum wind speed of 9,8 m/s

Simulation results give 189,4 kW.

IGEC-198




CONFERENCE

It is obvious that the calculation and simulation results are close. Therefore, the simulation shows the feasibility of a real turbine-asynchronous generator system. It is possible to use MATLAB simulation data to perform the design of the wind turbine plant.

IGEC-198

THANK YOU



CONFERENCE

PrPreepared bypared by : : Nur BekirogluNur Bekiroglu [email protected] Zehra YumurtacıZehra Yumurtacı

[email protected] Bedri KekezoğluBedri Kekezoğlu bkekez@yildiz

.edu.tr

IGEC-198

Documents

MAXIMUM POWER GENERATION USING WIND POWER PLANTS Prepared by: Nur Bekiroglu Zehra Yumurtacı Bedri Kekezoğlu YILDIZ TECHNICAL UNIVERSITY IGEC-2 INTERNATIONAL