the main objective of the use of wind turbine is generating electricity

7/26/2019 The Main Objective of the Use of WIND Turbine is Generating Electricity

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NEED FOR CONTROL SYSTEM.

.The main objective of the use of WINDturbine is generating electricity.

.The power output P, from a wind turbine

is given by the epression!


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. Electrical energy generated form a

wind turbine varies as the cube of

wind speed.

.The power _ wind velocity contains

four regions:

1) Wind speed < cut _ in speed:

at this region the eciency is not

accepted.

!) Wind speed "cut _in speed:at this region the wind turbine

starting to wor#.


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$) Wind speed "rated speed :

at this speed the generator wor#ing

at speci%ed rated power.

&) Wind speed '" cut _out _speed:

that may causes damage the wind

turbine

and causes the damage of the

generator.

. (o we need to control system for:

1) capture rated power.

!) *rotect the wind turbine from high

wind turbine.

$) When generator disconnected

suddenly prevent the rotor from

runaway.

&) +irection control.

Drag & lift forces


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.,ift is de%ned to be the component

of this force that is perpendicular to

the oncoming -ow direction.

.+rag is de%ned to be the

component of this force that is in thesame direction the oncoming -ow

direction.


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"ngle of attac# is the angle between the

lifting body$s reference line and theoncoming %ow.

. The critical angle of attac# is the angle

of attac# which produces maimum lift

coe&cient.


6/41

Power control

. y far the most e/ective way of

in-uencing the aerodynamic angle

of attac# and thus the input

power is by mechanically

ad0usting the rotor blade pitch

angle for this purpose in general

the rotor blade is turned about its

longitudinal ais with the aid of

actively controlled actuators.


7/41

.*ower control by changing the

aerodynamic angle of attac# of

the rotor can be achieved by two

methods:

2) the conventional approach is by

ad0usting the angle of attac# of

the blade to a smaller angle in

order to reduce power input.

3onversely increasing the angleof attac# increases the power

input.


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. 22) The other possibility is to

change the blade pitch angle to a

larger angle of attac# up to theso4called critical aerodynamic

angle of attac# at which point the

air-ow separates at the surface of

the rotor blades thus limiting the

aerodynamic power input.

. This e/ect is #nown as a stall.

Active itc! control

. 2n general the rotor blade is

turned about its longitudinal ais

with the aid of

actively controlled actuators..There is two types of active pitch

control.


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2) F"ll#san itc! control$ rotating

all each blade about its ais in

the direction which reduces the

angle of attac#.22) Partial#san itc! control$ %

a'("sting t!e itc! of onl )*

to +,- of t!e %la'e lengt! is

sucient from the point of

view of aerodynamic eciency.


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la'e itc!ing 'rive

The main distinguishing feature of

blade pitching systems is the type of

drive.

.there is two types:


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2) 5ydraulic drives 22) electrical

drives

/'ra"lic la'e Pitc!

Sste0s

.(upply of the actuators is commonly

housed at a %ed location in thenacelle so that the supply lines must

be routed through the gearbo and

the hollow rotor shaft into the hub.


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. To reach the rotating hub from the

stationary nacelle a sealed hydraulic

rotary transmissionlead through is re6uired.

.Three hydraulic actuators are

installed outside the rotor hub. The

hydraulic supply and return lines for


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the actuators are routed through the

hollow rotor shaft and through the

gearbo into the rear part of thenacelle to the pressure supply

system located there which consists

of a motor4driven pump and pressure

accumulators.

. The actuators are controlled by

means of control valves via a change

in mass -ow or control pressure.


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. To avoid having to use a rotary lead

through one can either locates the

entire hydraulic system in therevolving hub or the actuators have

to be installed in a %ed position in

the nacelle.

2n the latter case the pitch

ad0ustment motion must be

transmitted into the revolving hub

by means of mechanical transmission

elements

.for eample a connecting rod The

hydraulic actuator wor#s against astrong spring so that in a

brea#down involving the complete

loss of system pressure the rotor

blades are forced into the feathered

position by the spring thus causing

the rotor to stop.

2n wind turbines with partial blade

pitching


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the pitch mechanism must be

installed in the outer blade area.

Electrical la'e Pitc!

Sste0s


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.The power supply for emergencypitch ad0ustment consists of two

batteries which are also located in

the rotor hub.

The %rst one of these was Enercon

where each rotor blade on theirmedium4si7ed range of turbines 8E4

&9) has its own electric pitch motor

mounted on the outside -ange ring

8igs. ;.1). =ther manufacturers

place the electric pitching drivecompletely inside the rotor hub

Stall control


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.a stall is a reduction in the lift

coecient generated by an airfoil as

angle of attac# increases.. This occurs when the critical angle

of attac# of the airfoil is eceeded.

. Where the angle of attac# increases

beyond a certain point such that the

lift begins to decrease.


18/41

. low separation %eginsto occur atsmall angles of attac# while attac!e'

-ow over the wing is still dominant.

>s angle of attac# increases the

separated regions on the top of the

wing increase in si7e and hinder thewing?s ability to create lift.

>t the critical angle of attac#

separated -ow is so dominant that


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further increases in angle of attac#

produce lesslift and vastly more

drag.

Yaw sste0

.@aw system has been used with all

hori7ontal ais wind turbines toorient the nacelle and the rotor as.

Aertical ais wind turbines do not

need a yaw system since their

vertical rotors can face the wind

from any direction.

.The wind direction changes.


20/41

F"nction

.the @aw system has two main

functions:

1)orienting the rotor and

the nacelle into the wind.

!) (ome turbines also

use active yaw as a means of power

control.

. @awing the rotor with respect to the

wind direction it reduces the

e/ective swept area with respect to

the wind direction.


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1ariations in win'

'irection

.variations of wind direction in time

can be divided into the following

categories:

. 2nter4annual

. >nnual.+iurnal

.(hort4term 8gusts and turbulence).


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. 2nter4annual:2nter4 annual

variations in wind direction occur

over time scales greater than oneyear.

. >nnual:(igni%cant variations in

seasonal or monthly.

. +iurnal 8time of day):large wind

variations also can occur on a

diurnal or daily time scale.

. (hort4term:(hort4 term wind

direction variations of interest

include turbulence and gusts.

2in' 'irectioninstr"0entation

.due to continuous change at wind

direction (o we need a winddirection sensor.

. Wind direction is normally

measured via


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the use of a wind vane.

. Wind vanes usually produce signals

bycontact closures or by

potentiometers.

.=ne type of wind that the use of

self4synchronous motors.


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.The transmitter T is mechanically

connected to a wind vane while the

receiver B is connected to a pointer

on an indicating instrument.

.oth rotors are connected to thesame source of ac.

.When the induced voltages are the

same and opposing each other

there will be no current -ow and no

rotor tor6ue.


25/41

. When the transmitter rotor is

moved voltage magnitudes become

unbalanced causing currents to -owand a tor6ue to be produced on the

receiver rotor.

. This causes the receiver rotor to

turn until it again is in alignment

with the transmitter rotor.

.=ther type of wind vane which

wor#s well for digital data system.

.2t consists of potentiometer a

voltage source A and an analog to

digital converter.


26/41

. The potentiometer is oriented so

the output voltage Advalue is

changes due to wind directionchanges.

. The >C+ converter converts Adto a

digital form for recording.

.Each digital number represents a

range of wind direction.

Tes


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'a

wTy

pe

'a

wTy

pe

y aw i n

gb yf a n (t a i l

w he e l

y aw i n

gb yf a n (t a i l

w he e l

awing % fan#tailw!eels

.@awing with the help of a fan4tail is

the simplest method.. @awing with the aid of a fan4tail

wheel can still be found in some

smaller turbines.


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.the fantail in the cap of the turbine.

. the fantail parallel to the air-ow

at this case it did not turn ..if the wind shifted it would begin to

turn the fantail .

.this would turn a shaft running from

the fantail

+own to wheels or a gear bo whichwould turn the turbine bac# into the

wind .


30/41

This has the advantage of not

re6uiring a separate power source

or controls.

free Yaw te

. Turbines with free yaw are normally

downwind machines..2f the rotor is positioned downwind

the point of attac# of the total

aerodynamic force of the rotor is

located behind the ais of rotation of

the tower head.


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.the yaw ais so that with the cross

wind force the aerodynamic forces

produce a restoring moment on the

rotor within a very wide yaw angle

range.

.2n turbines with free yaw the yaw

system is normally much simpler.

. =ften there is nothing more than

the yaw bearing..ree yaw machines sometimes

incorporate yaw dampers to limit the

yaw rate.


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Active Yaw te

. Dpwind turbines normally have

some type of active yaw control.

. This usually includes:

. =ne or more yaw motors gears

.bra#e to #eep the turbine stationaryin yaw when it is properly aligned.

. The speed must be reduced so that

the yaw rate is slow and so that

ade6uate tor6ue can be suppliedfrom a small motor.


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Yaw %earing. Begardless of the type of yaw system

all hori7ontal ais wind turbines have

some type of yaw bearing.

.The primary component is a large

bearing that connects the main frame tothe tower.

. 2t serves as a rotatable connection


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between the tower and the nacelle of

the wind turbine.

.2n a turbine with active yaw theyaw bearing includes gear teeth

around its circumference.

.@aw damping is desirable even during

the yawing in order to avoid unwanted

yawing oscillations.

.These re6uirements can be met both by

a

conventional roller bearing.

Yaw %ra3es


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.yaw bra#e system comprising:

. +is# bra#e.

.ra#e caliper.

. 3aliper actuator 8hydraulic).

.When not yawing the machinery is

positively loc#ed by means of several

yaw bra#e calipers acting on a bra#e

disc.

.dis# bra#e is a device for slowing or

stopping the rotation of while it is in

motion.


36/41

'a

wdr

ive

hy

drau

l icsy

ste

)l e

ct ri ca l

syst

em

. To stop the wheel friction material

in the form of bra#e pads is forced

mechanically hydraulicallypneumatically or electromagnetically

against both sides of the disc.

The bra#e caliper is the assembly

which houses the bra#e pads and

pistons.

Yaw 'rive

. The yaw drive is the name given to

the mechanism used to rotate the

nacelle with in order to #eep theturbine facing into the wind.


37/41

. The two choices for the yaw drive

are hydraulic or electrical

components.the hydraulic system name lower

costs smaller si7e and also higher

tor6ue as advantages.

. Each yaw drive consists of powerful

electric or hydraulic motor with its

electric drive and

a large gearbo which increases the

tor6ue.

Yaw Control. There are two aims of control

system:

.1) the deviation of the rotor from

the wind direction the yaw angle is

supposed to be as small as possible

to avoid power loss.


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.!) The yaw control system must not

respond too sensitively to avoid

continuous small yaw movementswhich would reduce the life of the

mechanical components.

. The yaw motion in an active yaw

system is controlled using yaw erroras an input.

.@aw error is monitored by means of

a wind vane mounted on the turbine.

. When the yaw error is outside the

allowed range for some period oftime the drive system is activated

and the turbine is moved in the

appropriate direction.

. The problem is to %nd a practicable

compromise as it is not possible toset up a general rule.

. The situation relating to theW>4F9

turbine will be given as an eample.


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. The wind measuring system of the

turbine provides a mean value of the

wind direction over a period of tenseconds.

.2f the deviation remains below $

degrees the yaw control system willnot be activated.

. 2f the yaw angle determined is

above this value the time until


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correction is determined in

accordance with a pre4programmed

function..2f the wind speed eceeds $F mCs

the rotor will not be yawed.

References

1_ Wind Turbines: undamentals Technologies>pplications Economics GErich5auH

!_ Wind Energy 5andboo# GTonyurtonH


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the main objective of the use of wind turbine is generating electricity

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