Civil Engineering Reference
In-Depth Information
FIGURE 8-17
Operating stability and electrical load matching with resistive load and constant power load.
shown in
Figure 8-17 (a)
is supplying the power to the resistive load R
, it
1
will operate at point A
. If the load resistance increases to R
or R
, the
1
2
3
operating point moves to A
, respectively. The maximum power is
extracted from the module when the load resistance is R
or A
2
3
(
Figure 8-17b
)
.
Such load matching with the source is always necessary for maximum power
extraction from the pv module.
The operation with constant power loads is shown in
Figure 8-17(c)
and
(d). The constant power load line has two points of intersection with the
source line, denoted by B
2
is stable, as any perturbation
from it will generate a restoring power to take the operation back to B
and B
. Only point B
1
2
2
.
2
Therefore, the system will operate at B
.
The necessary condition for the electrical operating stability of the solar
array is as follows:
2
dP
dV
dP
dV
>
(8-10)
load
source
Some loads such as heaters have constant resistance, with power varying
with the voltage squared. On the other hand, some loads such as induction
motors behave more like constant power loads, drawing more current at
lower voltage. In most large systems with mix loads, the power varies
approximately in linear proportion with voltage.
8.6.7
Sun Tracking
More energy is collected by the end of the day if the pv module is installed
on a tracker, with an actuator that follows the sun like a sunflower. There
are two types of sun trackers:
