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INDUCTION
GENERATOR
FOR
WIND
POWER
GENERATION
OUTLINES
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INTRODUCTION
HISTORY
WIND TURBINES
TERMINOLOGIES USED
WORKING
CONTROLLING
ADVANTAGES OF VARIABLE SPEED
GENERATION
WHY INDUCTION GENERATOR?
ADVANTAGES & DISADVANTAGES OF WIND
ENERGY
APPLICATIONS
CONCLUSION
INTRODUCTION
Wind
turbines convert the kinetic energy present
in the wind into mechanical energy by means of
producing torque.
Large scale wind power projects are an attractive
alternative to conventional capacity expansion.
In the present scenario , most wind turbine
manufacturers now equip power generating units
by induction generators.
They are operated either at fixed speed or
variable speed.
Generators driven by fixed speed turbines can
directly be connected to grid.
Variable speed generators need a power
electronic converter interface for interconnection
with the grid.
Variable speed generation is preferred over fixed
speed generation.
HISTORY
In 200 B.C., in ancient
Persia , the earliest
windmills were used to grind
grain.
These early devices
consisted of one or more
vertically-mounted wooden
beams , on the bottom of
which was a grindstone,
attached to a rotating shaft
that turned with the wind.
Starting in the 11th century
A.D. , European crusaders
brought the concept and
developed the DUTCH type
wind mill.
The first automatically
operating wind turbine for
electricity generation.
It was built by Charles F.
Brush in 1887-1888 in his
backyard.
Charles’s 60 foot , 80,000
pounds turbine supplied 12
kW power to 350
incandescent lights.
Its rotor was 17 meters in
diameter.
WIND TURBINES
Wind
turbines convert wind energy to electricity for
distribution.
Aerodynamic
modeling is used to determine the
optimum tower height, control systems, number of blades
and blade shape.
Wind
turbines are generally classified depending on
their axis of rotation as:
-Horizontal axis type,
-Vertical axis type.
The
horizontal axis types generally have better
performance.
A
quantitative measure of the wind power available at
any location is called Wind Power Density(WPD).
Commercial
wind farms generally produce a WPD of 400
watts/square meter.
HORIZONTAL AXIS WIND TURBINE
AALBORG-TURBINE
VERTICAL AXIS WIND TURBINE
DARRIEUS-WINDMILL
 The ROTOR component : Its approx 20% of the wind turbine
.
cost, includes the
blade for converting wind energy to low
speed rotational energy.
 The GENERATOR component : Its approx 34% of the wind turbine
cost, includes electrical generator ,the control electronics and a
gearbox.
.
 The STRUCTURAL component : Its approx 15% of the wind turbine
cost, includes the tower and yaw mechanism.
TERMINOLOGIES USED
ANEMOMETER:
IT’S A WIND DIRECTION SENSOR WITH DIGITAL DISPLAY.
USED IN AREAS WHERE AC POWER IS NOT AVAILABLE. MONITORS WIND SPEED
AND STORE MAX AND AVERAGE VALUE.
YAW SYSTEM: THEY PERFORM THE TASK OF ORIENTING THE ROTOR IN THE
DIRECTION OF WIND.
NACELLE: IT IS STRUCTURE THAT HOUSES ALL OF THE GENERATING
COMPONENTS LIKE-GEARBOX, ROTOR SHAFT AND BRAKE ASSEMBLY ETC.
ROTOR BLADES: THE BLADES ARE THE SAILS OF THE SYSTEM ,
WHEN THE WIND FORCES THE BLADES TO MOVE
OF ITS ENERGY TO THE ROTOR.
, IT HAS TRANSFERRED SOME
.
SHAFT SYSTEM:
THE WIND TURBINE SHAFT IS CONNECTED TO THE CENTRE
OF THE ROTOR , WHEN THE ROTOR SPINS THE SHAFT SPINS AS WELL.THUS ROTOR
TRANSFERS ITS MECHANICAL ROTATIONAL ENERGY TO THE SHAFT.
WIND VANE:
SMALL TURBINES ARE POINTED INTO THE WIND BY USING IT.
GEAR BOX: IT TURNS THE SLOW ROTATION OF THE BLADES INTO A QUICKER
ROTATION THAT IS MORE SUITABLE TO DRIVE AN ELECTRICAL GENERATOR
WORKING
Aeroturbines convert wind energy into rotary mechanical energy.
A mechanical interface , consisting of a step –up gear and a
suitable coupling transmits the energy to an electrical generator.
The output of this generator is connected to the load or system
grid.
The controller senses the wind direction ,wind speed , power
output of the generator and other necessary performance
quantities of the system and initiates appropriate control signals to
take suitable corrective actions.
Several schemes for electrical generation have been developed.
These schemes can be broadly classified under these categories:
1. Constant speed generation system.
2. Variable speed generation system.
As constant speed generation system suffer from a number of
drawbacks hence variable generation system is preferred .
WIND
TURBINE
WIND
GEARING
AND
COUPLING
WT
WT
ELECTRICAL
GENERATOR
GC
EG
TO LOAD
UTILITY GRID
PITCH
CONTROL
YAW
CONTROL
SPEED
CONTROL
SIGNAL
GEN.
TEMP.
CONTROLLER
COMPONENTS OF WIND ELECTRIC SYSTEM
VARIABLE SPEED WIND ENERGY CONVERSION SYSTEM
In variable speed systems, the turbines rotor absorbs the mechanical
power fluctuations by changing its speed.
So the output power curve is smoother which greatly enhances the
quality of power.
However ,since variable speed operation produces a variable
frequency voltage, a power electronic converter must be used to
connect to the constant frequency grid
It can be achieved by using:
WECS with Squirrel cage induction generator.
WECS with Wound rotor induction generator.
WECS with Doubly-fed induction generator.
WECS with Squirrel cage induction generator
In this set up the stator of the squirrel cage induction generator will be
connected to the grid by the means of back to back connected power
electronic converter bridges.
Since the power converter has to convert all the stator power, the converter
size depends on the stator power rating.
ADVANTAGE:
Ability to make the best use of available wind power.
It eliminates the need for a capacitor bank.
DISADVANTAGE:
Cost of power converter is high.
WECS with Wound rotor induction generator
The power converter size in the earlier system can be reduced by using it
on the rotor side of a wound rotor induction generator. Above fig shows a
variable speed system using a wound rotor generator. The power converter
is now connected between the rotor and grid , so it needs to carry only the
slip power.
ADVANTAGES:
For utility scale wind power generation it outweighs squirrel cage
machine.
WECS with DFIG
Double-fed induction machines can be operated as a generator as well as a
motor in both sub-synchronous and super-synchronous speeds, thus giving
four possible operating modes.
Only the two generating modes at sub-synchronous and super-synchronous
speeds are of interest for wind power generation.
BACK TO BACK CONNECTED POWER CONVERTER BRIDGES
Two power converter bridges connected back-to-back by means of a dc link can
accommodate the bidirectional rotor power flow in a DFIG.
The purpose of the grid side converter is to maintain the dc link voltage constant.
It has control over the active and reactive power transfer between the rotor and
the grid.
The rotor side converter is responsible for control of the flux, and thus, the stator
active and reactive powers .
ADVANTAGES:
Less cost of AC-AC converter.
Improved system efficiency.
WIND POWER DEVELOPED BY THE WIND TURBINE IS
GIVEN BY :
P=(Cp AρV^3)/2
Where
Cp: Power coefficient
A: Area swept by rotor blades
ρ: Air density
V: Velocity of wind
CONTROLLING
Induction generator control:
Cage rotor induction generators can be made to operate over
a wider speed range by pole changing or pole amplitude
modulating the main winding.
A Wound rotor induction generator can be controlled by
varying the slip energy of the rotor circuit using following
methods : rotor resistance control , cascading etc
A bank of capacitors connected to the terminals can be used.
Transmission control:
By using silicon controlled rectifier device.
Conduction period of electronic devices can be controlled by
applying delayed trigger pulses.
Load control:
Using switched load resistors stepwise load approximation can
be made .
Operation within the maximum current loading of the
generator can be set.
ADVANTAGES OF USING VARIABLE
SPEED GENERATION
Better
energy capture than fixed speed
generation.
Mechanical
Acoustic
Cost
stress reduction of turbine.
noise reduction.
effective and entirely feasible.
WHY INDUCTION GENERATOR?
Simple
and robust construction.
Can run independently.
Inexpensive.
Minimal maintenance.
Inherent overload protection.
At high speed, reduces size and weight of
machine(roughly 0.33m long, 0.5m diameter)
and filter components.
Wind turbine data
The wind turbine is a MOD 5 type with the following data
Nominal values
Turbine
1.8 MVA
Rated wind speed
7 m/s
Rotor radius
40 m
Rotor swept area
5026.548 m2
Air density
1.225 kg/m3
Gear box efficiency
0.979 pu
Gear ratio (machine/turbine)
120
ADVANTAGES OF WIND ENERGY
It
is a renewable source of energy.
Wind
power systems are non-polluting.
Wind
energy systems avoid fuel provision and
transport.
On
a small scale upto a few kilowatt system is less
costly.
DISADVANTAGES OF WIND ENERGY
Wind
energy available is fluctuating in nature.
Wind
energy needs storage capacity because of
its irregularities.
Wind
Wind
energy systems are noisy in operation.
power systems have a relatively high overall
weight.
APPLICATIONS OF WIND ENERGY
In
various industrial process like: food processing, textile
processing , production of inorganic chemicals like chlorine,
bromine etc
Wind
powered pump can be used to desalinate water.
The
powerful turbines(50kW), are for operating irrigation
pumps , navigational signals and remote communication.
In
aqueduct system , large scale wind driven units can
provide power for the pumping of water from the main
reservoir to auxiliary reservoir.
CONCLUSION
Wind
is one of the most flexible and tractable of all
energy sources, since the mechanical energy derived
directly from the wind can be readily and efficiently
converted to other forms of energy.
The
cost of power generation from wind farms has now
become lower than diesel power and comparable to
thermal power in several areas of our country especially
near the coasts.
Thus
Wind power can be used in centralized utility
applications to drive synchronous AC electrical
generators.