Wind turbine modeling using pitch controller

Presentation on Wind turbine modeling using pitch controller

OBJECTIVES

1. Modeling of a wind turbine where pitch angle is a control variable.
2. 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

1. 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.
2. The Cp (λ, β) characteristic gives us a power coefficient, that depends on the tip speed ratio λ and the pitch angle β .
3. 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.
4. 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.
5. 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 ratio

Beta = Pitch angle

Cp = Rotor power coefficient

NEED OF PITCH CONTROLLER

1. Because of the fluctuating nature of the wind speed the output of the wind turbine varies.
2. At the high wind speed, fatigue damage can be occurred to the mechanical parts of the wind turbine.
3. 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.
4. 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 VESTAS-V52 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
Cut-in wind speed	4m/s
Nominal wind speed	16m/s
Cut-out 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