• 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
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
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:
Direction of wind
Mechanical gears involved in its design
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].
Model For Wind turbine
Wind turbine extracts portion of wind and converts it into mechanical Power.
It has three inputs
The Blade Pitch Angle
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
No external dc excitation is needed.
Less losses and improved efficiency
The mechanical power of wind turbine provide torque to the generator
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
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
The boost converter then converts the DC rectified value into a constant DC value
Finally the inverter is used to convert the constant dc Voltage into Ac with Constant
frequency and Voltage Magnitude
Permanent Magnet Synchronous Generator
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
Power ratings ranging from few watts to 100kW or more.
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.
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
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.
SQUIRREL CAGE INDUCTION GENERATOR
To make best use of wind energy available
It is only used in large scale applications.
A squirrel cage induction generator always consumes reactive power.
So capacitor is needed to control the reactive power.
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.
Advantages and Disadvantages
For utility scale wind power generation it outweighs squirrel cage
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.
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 rotor side converter is responsible for control of the flux, and thus, the stator
active and reactive powers .
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
Generation of electrical power at lower wind speeds.
High Temperature Superconducting
Wind Turbine Generators
HIGH CURRENT DENSITY
HIGH MAGNETIC FIELD
REDUCTION IN MASS AND SIZE
HIGHER PARTIAL LOAD EFFICIENCY
POWER RATING 5-10 MW
USED SPECIALLY IN OFFSHORE
Increase machine efficiency beyond 99%, reducing losses by as much as 50% over
Reduced pollution per unit of energy produced
Lower life-cycle costs
Enhanced grid stability
Reduced capital cost
Reduced installation expenses