User manual

Page 51
EA Elektro-Automatik GmbH
Helmholtzstr. 31-37 • 41747 Viersen
Germany
Fon: +49 2162 / 3785-0
Fax: +49 2162 / 16230
www.elektroautomatik.de
[e-mail]
EL 3000 B Series
3.9.10 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 electronic load simulates this behaviour by a function. 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 connected to its AC output. Furthermore, all MPP tracking
related parameters of the load can be adjusted and it so is much
moreexiblethananinverterwithitslimitedDCinputrange.
For evaluation and analysis purposes, the load can also record
measured data, i. e. DC input values such as actual voltage, cur-
rent or power, to USB stick or provide them for reading via digital
interface.
The MPP tracking function, as it is manually usable on the HMI,
offers three modes. A fourth mode is available for remote control
via any of the optionally available digital interfaces (USB, Ethernet).
3.9.10.1 Mode MPP1
MPP
Power
Voltage
Thismodeisalsocalled“ndMPP”.Itisthesimplestoptiontohavetheelectronicload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 load 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 load 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...Nominal value of U Voltage of the solar panel when unloaded, taken from the panel specs
I
SC
0...Nominal value of I Short-circuitcurrent,max.speciedcurrentofthesolarpanel
Δt 5 ms...65535 ms IntervalformeasuringUandIduringtheprocessof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 off the DC input. The
acquired MPP values of voltage (U
MPP
), current (I
MPP
)
and power (P
MPP
) are then 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take
already a few seconds.
3.9.10.2 Mode MPP2
This mode tracks the MPP, so it is closest to the operation of
a 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sinkbefore
the direction is reversed and the voltage starts to rise again
until the load reaches the MPP. The result is a zigzag shaped
curve of both, voltage and current.
A typical curve display is shown in the picture to the right.
For the example, 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.