Presentation on Wind turbine modeling using pitch controller
OBJECTIVES Modeling of a wind turbine where pitch angle is a control variable.
 At the high wind speed the pitch controller will automatically active to maintain the output power at the rated level.
PITCH ANGLE AS A CONTROL VARIABLE
 The amount of energy that is extracted from wind and converted into mechanical energy is depending on the radial force acting on the blade. The formation of the force depends on particular profile design and dimension.
 The Cp (λ, β) characteristic gives us a power coefficient, that depends on the tip speed ratio λ and the pitch angle β .
 For blade profiles two forces are generally used to describe the characteristics, lift force component (F_{LIFT} ) and a drag component (F_{DRAG}) which resulting as F_{TOTAL}.
 The F_{LIFT} component and a F_{DRAG} together are transformed into a pair of axial F_{THRUST }force and rotor's directions F_{TORQUE} components, where only the F_{TORQUE} produces the driving torque around the rotor shaft. By varying the pitch angle, β the size the direction of F_{TOTAL }components can be changed.
 The axial forces F_{THRUST }has no driving effect but puts stress on rotor blades and furthermore, leads to a thrust on the nacelle and on tower.
AERODYNAMIC FORCES AND VELOCITIES AT ROTOR BLADE
POWER COEFFICIENT VS TIP SPEED RATIO CURVE WITH DIFFERENT VALUE OF PITCH ANGLE
Power coefficient surface
Where,
Lamda = Tip speed ratioBeta = Pitch angleCp = Rotor power coefficient
NEED OF PITCH CONTROLLER
 Because of the fluctuating nature of the wind speed the output of the wind turbine varies.
 At the high wind speed, fatigue damage can be occurred to the mechanical parts of the wind turbine.
 By controlling the pitch angle the output power can be limited as the wind turbine rotor power coefficient decreases with the increase of pitch angle.
 At the high wind speed the automatically activated pitch controller keep the output power within rated level by increasing the value of pitch angle.
BLOCK DIAGRAM
Wind turbine scheme with pitch controller
BLOCK DIAGRAM
Pitch actuator system
OPERATIONAL WAVE SHAPE
MATHMATICAL EXPRESSIONS
The mechanical output power equation is given by,
And the expression for power coefficient is given by,
Where,
MODEL SPECIFICATIONS
The specifications of the wind turbine VESTASV52 are given in the following table.
Rotor
diameter

52m

Area
swept

2124m2

No
of blades

3

Power
regulation

Pitch/opti
speed

Air
brake

Full
blade pitch

Cutin
wind speed

4m/s

Nominal
wind speed

16m/s

Cutout
wind speed

25m/s

Nominal
output

850kw

METHODOLOGY
SIMULINK BLOCK OF WIND TURBINE MODEL FOR VESTAS V52
SIMULINK MODEL OF PI CONTROLLER
SIMULINK MODEL OF PITCH ACTUATOR
SIMULATION RESULT
The simulation results obtained from the MATLAB/SIMULINK wind turbine model are given below(for various wind speed)
Wind
speed(m/s)

Pitch
angle
(degree)

Cp

Power(pu)

16(rated)

0

0.1595

1

17

6.22

0.1138

1

19

12.98

0.11

1

RESULT ANALYSIS
From simulation result, we observed that, at rated wind speed pitch angle is zero i.e. pitch controller remains inactive and above rated wind speed the pitch controller is activated and keep the output power at rated value by changing the value of pitch angle.
By using pitch controller the output power has been limited at high wind speed and wind turbine can operate safely. The simulation results has been shown that at the wind speed above the rated speed of the turbine the pitch controller automatically activate and limiting the output power by increasing the pitch angle.
Submitted by Sudipta Dey and Md. Mazedul Huq