Siemens SINAMICS S120 System Manual page 58

Detailed descriptions of the function modules
6.2 Controls for grid droop operation
control. At the same time, a DC component controller suppresses possible DC fault
components in the phase voltages, which would otherwise result in transformer saturation
effects and power oscillations in the grid.
Providing high short-circuit currents to clear grid faults (trip fuses) is another important
requirement placed on power generating systems. Here, a fast current controller allows
(non)symmetrical grid faults for single generator operation – or together with other power
generating sources – to be reliably ridden through (FRT). After a short circuit has been
cleared, the power generating units are resynchronized without requiring any additional
communication resources. For continuous, ongoing grid faults, after a defined time, a grid
monitoring function shuts down and prevents short-circuit currents from being maintained
when it comes to internal plant/system faults.
For use in microgrids, in addition to the power grid and island grid mode, all conceivable
operating changes must be supported (diagram above, marked in gray).
● Black start
This function involves establishing the island grid voltage u
voltage of zero, with disconnector 2 to the external grid open.
● Island grid synchronization
In operation, this function block adapts amplitude, frequency and phase position of the
island grid voltage to an external grid u
an almost no-current condition, and coordinated by a higher-level management system –
power can be exchanged between a micro grid and power grid.
● Operating mode change
Also when disconnector 2 is open, it can make sense to switch over a power generating
system from the voltage source mode into the current-impressing mode. For example,
this applies if a sufficient number of grid formers is active so that individual regenerative
power generators (for example, photovoltaic systems) can operate with their maximum
power as a current source.
58
, u
12isl
, u . Disconnector 2 can then be closed in
12ext 23ext
System Manual, 04/2015, A5E03347436A
starting from a
23isl
Grid infeed