User Manual

Page 85
EA Elektro-Automatik GmbH
Helmholtzstr. 31-37 • 41747 Viersen
Germany
Fon: +49 2162 / 3785-0
Fax: +49 2162 / 16230
www.elektroautomatik.de
[e-mail]
PSB 9000 2.5 kW Series
3.11.17 MPP tracking function
MPP stands for the maximum power point (see principle view
to the right) on the power curve of solar panels. Solar inverters,
when connected to such panels, constantly track this MPP once
it has been found.
The device imitates this behavior in sink mode. It can be used to
test even huge solar panels without having to connect a usually
big solar inverter device which also requires to have a load con-
nected to its AC output. Furthermore, all MPP tracking related
parametersoftheloadcanbeadjustedandit’sthusmoreexible
than an inverter with its limited DC input range.
For evaluation and analysis purposes, the device can also record
measured data, i. e. DC input values such as actual voltage,
current or power, to USB stick or provide them for reading via
digital interface.
The MPP trackingfunction o󰀨ersfour modes. Unlike with the
manual handling of other functions, values for the MPP tracking
are only entered by direct input via the touch screen.
MPP
Power
Voltage
3.11.17.1 Mode MPP1
This mode is also called “nd MPP”.It’sthesimplestoptiontohavethedevicendtheMPPofaconnectedsolar
panel. It requires to set only three parameters. Value U
OC
isnecessary,becauseithelpstondtheMPPquicker
as if the device would start at 0 V or maximum voltage. Actually, it would start at a voltage level slightly above U
OC
.
I
SC
is used as an upper limit for the current, so the device would not try to draw more current than the panel is
speciedfor.FollowingparameterscanbeconguredfortrackingmodeMPP1:
Value Range Description
U
OC
0...U
Nom
Voltage of the solar panel when unloaded, taken from the panel specs
I
SC
0...I
Nom
Short-circuit current, taken from the panel specs
Δt 5 ms...60000 ms TimebetweentwotrackingattemptswhenndingtheMPP
Application and result:
After the three parameters have been set, the function can be
started. As soon as the MPP has been found, the function will stop
andswitcho󰀨theDCinput.TheacquiredMPPvaluesofvoltage
(U
MPP
), current (I
MPP
) and power (P
MPP
) would then be shown in
the display.
ThetimeofafunctionrundependsontheparameterΔt.Even
with the minimum setting of 5 ms one run usually takes already
a few seconds.
3.11.17.2 Mode MPP2
This mode tracks the MPP, so it’s closest to the operation of a real
solar inverter. Once the MPP is found, the function won’t stop, but
try to track the MPP permanently. Due to the nature of solar panels
this can only be done below the level of the MPP. As soon as this
point is reached, the voltage starts to sink further and so does the
actual power. The additional parameter ΔPdeneshowmuchthe
power may fall before the direction is reversed and the voltage
starts to rise again until the load reaches the MPP. The result are
zigzag shaped curves of both, voltage and current.
Typical curves are shown in the picture to the right. For the ex-
ample the ΔP was set to a quite small value, so the power curve
looks almost linear. With a small ΔP the load would always track
close to the MPP.