Types of Alternators used in windmills

1. Alternators in windmills
Presented by,
R.Vasanthan – 14E113
V.Sai Krishna – 14E95
P.Vinith – 14E123
S.Padmanathan – 14E82

2. Fundamentals
• Wind Power
o Harnessed by using wind flow as the
driving force of the generator in order to
create a torque on the rotor and in effect
produce electricity.
o Wind is Uncontrollable => Special
generators are needed
o For constant rotor speed: some wind
turbines have motors/controllers that
drive the blades when the wind is not
strong enough

3. Planetary gear set arrangement

5. Types of generators
• Induction Generator
• Permanent Magnet Synchronous
Generators

6. Wind Turbines Generation System
Wind Turbine
Permanent
magnet
synchronous
generator
Rectifier
Boost
Controller
Inverter

7. Wind turbine
 The wind turbine is playing a cardinal role in the entire system as it is responsible
for the generation of mechanical power needed to drive the generator.
 The primary factors on which the wind turbine performance depend are:
 Wind speed
 Direction of wind
 Blade size
 Pitch angle
 Mechanical gears involved in its design

8. Mathematical model of wind turbine
 The wind turbine can be represented in terms of a mathematical equation, which
governs its generated power.
Pm=mechanical output power of the turbine
Cp=D the air density [kg/m3],
cp the performance coefficient or power coefficient,
λ the tip speed ratio vt/vw, ( the ratio
between the blade tip speed vt and the wind speed
upstream the rotor vw [m/s])
Ѳ the blade pitch angle [deg], and
Ar the area swept by the rotor [m2].

9. Model For Wind turbine
 Wind turbine extracts portion of wind and converts it into mechanical Power.
 It has three inputs
 Generator Speed
 The Blade Pitch Angle
 Wind speed.
 One Output
 Torque

10. Generator
 The prime mover rotor of the (PMSG) is driven by Wind turbine mechanical Power.
 We have selected PMSG (5kW) because for small scale level PMSG is considered as
best type of generator.
 better reliability, less maintenance and
 more effective
 No external dc excitation is needed.
 Less losses and improved efficiency

11.  The mechanical power of wind turbine provide torque to the generator
shaft.
 The output generated by PMSG is variable in magnitude and Frequency
because of the fluctuating wind speed.
 The output of the generator is fed
via stator into the rectifier block to
convert it into dc and smoothen it

12. Rectifier and controlled boost Converter
 For controlling the Ac output to a constant magnitude and frequency .
 Convert the AC (Variable Frequency and Voltage) from generator to a DC using
Rectifier.
 The boost converter then converts the DC rectified value into a constant DC value

13. Inverter
 Finally the inverter is used to convert the constant dc Voltage into Ac with Constant
frequency and Voltage Magnitude

14. Permanent Magnet Synchronous Generator
Advantages
 Don't require external excitation => Less power dissipation.
 Space is not needed for windings => smaller
 machine size (30% reduction in weight) and some cases cheaper.
 Smooth stator structure unlike their salient pole structure in conventional
dc machines.
 Power ratings ranging from few watts to 100kW or more.
Disadvantages
 Risk of demagnetization due to excessive currents in the motor windings
or due to overheating the magnet.
 Limited air gap flux density that permanent magnets can produce.

15. Squirrel Cage Induction Generator
 Stator of the SCIG is connected to grid through back to back power
electronic converter bridges
 The slip, and hence the rotor speed of a squirrel cage
induction generator varies with the amount of power
generated.
 These rotor speed variations are, however, very small,
approximately 1 to 2 per cent.
 Therefore, this wind turbine type is normally referred
to as a constant speed or fixed speed turbine.

16. SQUIRREL CAGE INDUCTION GENERATOR
 Advantages
To make best use of wind energy available
It is only used in large scale applications.
 Disadvantage
Expensive
A squirrel cage induction generator always consumes reactive power.
So capacitor is needed to control the reactive power.

17. Wound Rotor Induction Generator
 Power Convertor size reduced by using it on rotor side of WRIG
 This is 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.

18. WRIG
Advantages and Disadvantages
 For utility scale wind power generation it outweighs squirrel cage
machine.
 Offers a lot of flexibility for wide range of speed control
 Used in high power applications in which a large amount of slip
power could be recovered
 Speed of WRIM was changed by mechanically varying external rotor
circuit resistance(simplest way)
 Major disadvantage is low efficiency due to additional loses in
resistor connected in the rotor circuit.

19. DOUBLY FED
INDUCTION
GENERATOR
 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 .

20. ADVANTAGES AND DISADVANTAGES
 Operation at variable rotor speed while the amplitude and frequency of the
generated voltages remain constant.
 Optimization of the amount of power generated as a function of the wind
available up to the nominal output power of the wind turbine generator.
 Virtual elimination of sudden variations in the rotor torque and generator output
power.
 Generation of electrical power at lower wind speeds.
 Complicated
 Maintainence

21. HTSWTG
High Temperature Superconducting
Wind Turbine Generators
 HIGH CURRENT DENSITY
 HIGH MAGNETIC FIELD
 REDUCTION IN MASS AND SIZE
 INCREASED EFFICIENCY
 HIGHER PARTIAL LOAD EFFICIENCY
 POWER RATING 5-10 MW
 USED SPECIALLY IN OFFSHORE

22. ADVANTAGES
 Increase machine efficiency beyond 99%, reducing losses by as much as 50% over
conventional generators
 Energy savings
 Reduced pollution per unit of energy produced
 Lower life-cycle costs
 Enhanced grid stability
 Reduced capital cost
 Reduced installation expenses

23. REFERENCES
 http://www.scribd.com/doc/27428761/Wound-Rotor-Induction-Motor
 http://cdn.intechopen.com/pdfs/14821/InTech-
High_temperature_superconducting_wind_turbine_generators.pdf
 http://www.labvolt.com/downloads/download/86376_F0.pdf
 http://www.azom.com/article.aspx?ArticleID=1083
 http://www.taplondon.co.uk/bwea_offshore/pdf/JohnHill.pdf