Safety
Unintentional Is-
landing Detec-
tion
Unintentional islanding
In the event of a grid failure or disconnection of a small part of the grid from the
higher-level utility grid, it is possible under special conditions for local loads and
inverters to establish unintentional islanding. If the generation and load (of both
active and reactive power) are balanced, the AC voltage and frequency can re-
main within the allowable limits. In this case, the inverter (without additional is-
landing detection) will continue feeding energy into the grid, will not automatic-
ally shut down, and will supply power to the local loads. This is an unwanted con-
dition. To prevent these situations, active or passive islanding detection methods
can be used.
Active islanding detection
The inverter's active islanding detection function detects unwanted islanding
situations, the inverter stops feeding energy into the grid and disconnects from
the AC grid at all poles.
The detection process is carried out using a grid frequency shift method (Active
Frequency Drift): In the event of short-term grid frequency changes, the inverter
feeds in an alternating current with a changed frequency (frequency shift). In the
event of an interruption to the grid, the AC voltage will also change its frequency.
There is a co-feedback effect, whereby the frequency is shifted so much that it
exceeds or falls below the permissible limits. This causes the inverter to stop
feeding energy into the grid.
In the case of three-phase inverters, the method is also able to detect islanding
on any individual phases. This function is an active islanding detection method,
since the inverter specifically changes its feed-in behaviour during the detection
process.
Parameter Range of values Standard
value
Description
"Unintentional
Islanding De-
tection."
On Active islanding detection
is activated.
Off Off Active islanding detection
is deactivated.
"Quality Factor" 0.1 ‑ 10.0 1.0 The higher this value, the
stronger/more aggressive
the frequency shift of the
island detection.
Higher values therefore
result in shorter island de-
tection times. However,
values that are too high
can also have a negative
effect on the voltage qual-
ity.
In contrast, there are passive methods that detect islanding based only on the
measurement of AC network variables. This group includes, for example, "Rate of
Change of Frequency (RoCoF) Protection".
Isolation monit-
oring
Isolation monitoring ("Iso Monitoring")
The inverter performs an isolation measurement at the DC terminals of the PV
generator before each connection (at least once a day). Isolation monitoring
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