Environmental Engineering Reference
In-Depth Information
Fig. 3.1
Structure of a typical wind energy conversion system
The wind turbine absorbs the energy from an air stream and drives the generator
to produce electricity. The control system is used to control both the machine side
and the grid-side PWM inverters. The former controls the speed of the generator to
rotate at the optimal speed and have the maximum active power extraction from
the wind at different environment conditions. The latter transforms the DC voltage
in the DC link to AC voltage, and further to the distribution power grid.
The input power to a wind turbine can be described as follows [
3
]:
P
w
¼
1
2
qpr
2
v
w
ð
3
:
1
Þ
where r is the turbine radius (m), v
w
the wind speed (m/s), q the air density
(generally it is 1.25 kg/m
3
).
The mechanical power generated by the wind turbine can be expressed as follows:
P
m
¼
C
p
ð
k
;
b
Þ
P
w
¼
1
2
C
p
ð
k
;
b
Þ
qpr
2
v
w
ð
3
:
2
Þ
where C
p
is the power coefficient of the turbine representing the efficiency of the
wind turbine, b the pitch angle, and k the tip speed ratio representing the status of
the turbine in different wind speeds and defined by
k
¼
x
w
r
v
w
ð
3
:
3
Þ
where x
w
is the turbine angular speed, as shown in Fig.
3.1
.
Assume the pitch angle b is zero, the power coefficient of the turbine can be
approximately expressed as follows [
14
,
15
]:
