PV Inverter
SMA America, LLC
148
SI5048U-TUS121440
Technical Description
If Sunny Boy inverters are connected to the AC side of the off-grid power system, the Sunny Island
must be able to limit their output power. This situation can occur when, e.g., the Sunny Island battery
is fully charged and the (solar) power available from the PV generator exceeds the power required
by the connected loads.
To prevent the excess energy from overcharging the battery, the Sunny Island 5048U recognizes this
situation and changes the frequency at the AC output. This frequency adjustment is analyzed by the
Sunny Boy. As soon as the grid frequency increases beyond the value specified by ”f
AC
-Start Delta”
the Sunny Boy limits its output power accordingly.
This function is shown in the following figure:
The different settings have the following meanings:
• f
0
refers to the base frequency of the micro grid created by the Sunny Island.
• f
AC
Delta– and f
AC
Delta+ refer to the maximum range in which the Sunny Boy is active relative
to f
0
, 60 Hz.
• f
AC
Start Delta refers to the frequency increase relative to f
0
, at which point the power
adjustment via frequency begins
• f
AC
Limit Delta refers to the frequency increase relative to f
0
, at which point the power
adjustment via frequency ends. The output power of the Sunny Boy at this point is 0 W.
If the value is below the f
AC
-Delta– limit or exceeds the f
AC
-Delta+ limit, the Sunny Boys disconnect
from the grid.
When FSPC is activated and the diesel generator in the off-grid power system is operating, the diesel
generator determines the frequency, and the Sunny Boys react to certain changes in the diesel
generator frequency. The diesel generators generally operate at 60 Hz under load. For this reason,
in most cases the Sunny Boys will deliver their entire power to the off-grid power system, even when
the generator is running.
If the current battery voltage (V
Bat
) is greater than the nominal battery voltage (V
Bat, nom
)
and is also to be synchronized with an external source (generator), the Sunny Island
temporarily increases the frequency and disconnects the Sunny Boys using the frequency
shutdown method (overfrequency). Afterwards, it synchronizes with the generator.
