Environmental Engineering Reference
In-Depth Information
illustrated in
Figure 2.15
. First, a light wind of 2.3 m/s was blown at the wind
turbine generator, and the start point marked in
Figure 2.15
was the initial
condition of the WEH system. The MPP tracker utilizes the closed-loop PI
controller to manipulate the duty cycle of the boost converter according to
Equation 2.6
, which in turn controls the input resistance of the boost con-
verter towards (left side) the optimal resistance value of 150
. Once the MPP
of the power curve for a wind speed of 2.3 m/s is reached, the closed-loop
resistance emulator controls the boost converter to maintain power harvested
from the wind turbine generator for all the other MPPs occurring at differ-
ent wind speeds. Referring to
Figure 2.15
, it is observed that the emulated
resistance
R
em
is maintained at around 150
with increasing wind speeds,
until the MPP of the power curve for a wind speed of 6.3 m/s, marked as the
end point in
Figure 2.15
, is reached. This shows that the dynamic condition
of the environment is well taken care of by the proposed closed-loop resistor
emulator of the designed boost converter.
The designed boost converter with the resistor emulation MPPT approach
has already been demonstrated to yield excellent performance in extracting
maximum power from the wind turbine generator, but this comes at the ex-
pense of additional power losses in the converter and its associated control,
sensing, and PWM generation circuits. Thus, it is necessary to investigate the
significance of these power losses as compared to the total harvested power.
The first investigation is to determine the efficiency of the boost converter
conv
as a function of its output load power
P
load
over its input DC power
P
dc
.
Taking the target deployment area with average wind speed of 3.62 m/s as
an example, the efficiency of the converter is calculated to be as follows:
V
out
/
P
out
P
in
∗
R
load
V
in
I
in
=
100%
=
∗
100%
conv
71
V
2
9
.
/
1200
=
14 mA
∗
100%
=
84%
(2.7)
1
.
15
V
∗
8
.
For all other wind speeds, the efficiencies of the boost converter are calculated
using
Equation 2.7
to be between 80% and 90%, and the computed results are
shown in
Figure 2.16
. As seen, even for a light wind speed condition where
the power harvested is small (around 2 mW), the boost converter is still able
to achieve a reasonably good efficiency of 86%. This exhibits the ability of
the DC-DC boost converter to attain high efficiency in a very low power
rating condition.
Another investigation being carried out is to determine the power con-
sumption of the associated control, sensing, and PWM generation electronic
circuits and its significance as compared to the harvested power. Based on the
voltage and current requirements of each individual component in the sens-
ing and processing circuits, the total power consumption of the electronic
circuits is calculated to be
P
consumed
=
P
sensing
+
P
pr ocessi ng
+
P
PWMgeneration
(2.8)
=
3
V
∗
(74
A
+
15
A
+
30
A)
=
0
.
357 mW
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