Environmental Engineering Reference
In-Depth Information
Figure 4.40
Structure of MPP Trackers
Control with differential changes
: Voltage and current are measured and their
differential change estimated. With
, we get
I
•
d
V
= -
V
•
d
I
(4.91)
i.e. the electronics must balance both quantities.
Control with characteristics method
: This method also measures voltage and
current. Starting with the open circuit voltage
V
A
=
V
OC
, voltage and current
are changed alternately in the following manner:
(
k
<1)
After a few steps, this method obtains two operating points, one to the left
and one to the right of the MPP; the controller oscillates between these points.
Various MPP trackers have difficulty in finding the optimal operating point
when the solar generator is partially shaded, in rapidly changing conditions or
for non-standard modules. Shading occurring over prolonged periods of time
can cause high losses; therefore, a good MPP tracker should also provide good
results for irregular operating conditions, in which multiple local maxima can
occur in the I-V characteristic (see Figure 4.28, p146). When an unusually low
generator power indicates a shading situation, the MPP tracker must scan
through the whole voltage range to find the maximum for the optimal power
output.
E
LECTRICITY
S
TORAGE
Types of batteries
Consumers are hardly ever connected directly to a solar generator. In reality,
photovoltaic systems are more complex. In the absence of any kind of storage,
