PV Inverters in Stand-alone Grid Systems SMA Solar Technology AG
144 SI5048-TB-TEN110340 Technical Description
This function is shown in the following figure:
The different settings have the following meanings:
•f
AC
= 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 PV inverter is active relative
to f
AC
= 0. Fac-delta– and Fac-delta+, for example.
•f
AC
Start Delta is the frequency increase relative to f
AC
= 0, at which point the power adjustment
via frequency begins.
•f
AC
Limit Delta is the frequency increase relative to f
AC
= 0, at which point the power adjustment
via frequency ends. The power of the PV inverter at this point is 0 W.
If the value is below the f
AC
Delta– limit or exceeds the f
AC
Delta+ limit, the PV inverters disconnect
from the grid.
When FSPC is activated and the diesel generator in the stand-alone grid is operating, the diesel
generator determines the frequency, and the PV inverters react to certain changes in the diesel
generator frequency. The diesel generators generally operate at 50 Hz under load. For this reason,
in most cases the PV inverters will deliver their entire power to the stand-alone grid, 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 PV inverters using the frequency
shutdown method (overfrequency). Afterwards, it synchronizes with the generator.
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