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# Alternators in windmill

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Types of Alternators used in windmills

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### Alternators in windmill

1. 1. Alternators in windmills Presented by, R.Vasanthan – 14E113 V.Sai Krishna – 14E95 P.Vinith – 14E123 S.Padmanathan – 14E82
2. 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. 3. Planetary gear set arrangement
4. 4. Types of generators • Induction Generator • Permanent Magnet Synchronous Generators
5. 5. Wind Turbines Generation System Wind Turbine Permanent magnet synchronous generator Rectifier Boost Controller Inverter
6. 6. 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
7. 7. 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].
8. 8. 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
9. 9. 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
10. 10.  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
11. 11. 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
12. 12. Inverter  Finally the inverter is used to convert the constant dc Voltage into Ac with Constant frequency and Voltage Magnitude
13. 13. 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.
14. 14. 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.
15. 15. 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.
16. 16. 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.
17. 17. 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.
18. 18. 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 .
19. 19. 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
20. 20. 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
21. 21. 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
22. 22. 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