Siemens SINAMICS S120 System Manual page 118

Commissioning
7.7 Commissioning the grid droop control
Damping grid oscillations
A good damping is achieved, for example with the setting p5413 = 50 % x p5407 and
p5414 = 10 % x p5409.
Damping can be additionally or alternatively increased using DT1 filter p5476.
Notes
● Changing amplitude and frequency can result in undesirable behavior/response of the
other components in the island grid. The application is responsible for checking the
suitability of all of the components.
● Influencing loads/consumers in the island grid:
The ramp times for the grid parameters to be synchronized must be selected, so that
loads/consumers are neither overloaded nor tripped as a result of a fault (p5586[1...6]).
● Interaction with other power generating units in the island grid:
The synchronizing grid infeed must be the only generating unit in the island grid that
controls the grid voltage and grid frequency. If other power generating units are involved
in the voltage and frequency control in the island grid, then the offset values for frequency
and voltage (r5582[0, 1]) must be communicated with these other power generating units
using a real-time-capable communication link.
● The 3rd VSM10 that is mandatory senses the grid voltage at the grid side of the circuit
breaker between the island grid and external grid (FP 7990).
The voltage measured values are displayed in r5461[1] / r5462[1] and are used as inputs
for the voltage conversion in the transformer model (p5487[2] = r5461[1], p5487[3] =
r5462[1]. The transformer ratio (between the external grid and the infeed input) is set
using p5486[1].
The phase shift of the voltage between the external grid and the grid filter voltage must
be set in parameter p6420[1].
The remaining gain errors (e.g. caused by measuring transformers) can be corrected
using parameter p6421[1].
● In order to guarantee reliable synchronization of the two grids, reliable values for
amplitude, frequency and angular position of the external grid are required.
These variables represent the setpoints for synchronizing the island grid.
A proven technique employs a phase-locked loop, i.e. a control loop for the stable
calculation of the variables being searched for from the measured actual values of the
external grid voltages.
The "Grid transformer" function module provides a generally usable PLL; the input
variable is a measured voltage vector in alpha/beta coordinates.
As a consequence, the following parameter assignments are required:
– The voltage values of the external grid converted into alpha/beta coordinates are
– PLL2 should be activated at the start of synchronization: p5571 = r5499.5
– The setpoints for voltage, frequency and angular position used for synchronization are
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connected with the PLL inputs: p5574[0, 1] = r5488[3, 4]
displayed in r6311[1], r6313 and r6314.
System Manual, 04/2015, A5E03347436A
Grid infeed