Notes For Commissioning Systems For Operation On Grids With Low Short-Circuit Power (Fault Level) And Variable Grid Parameters - Siemens SINAMICS S120 System Manual

Commissioning
7.11 Notes for commissioning systems for operation on grids with low short-circuit power (fault level) and
variable grid parameters
7.11 Notes for commissioning systems for operation on grids with low
short-circuit power (fault level) and variable grid parameters
Especially in island grids, test grids or when connecting to long grid cables, frequently – in
comparison to the Active Line Module rated power – there is a low grid short-circuit power
available (e.g. RSC values < 10). Such a "weak" grid manifests a high inductance at the
Active Line Module connection point. The resonance properties of the system from the grid
and Active Interface Module change significantly and require that the control is appropriately
adapted.
Using the grid data identification (p3410 = 4 or 5), normally, the necessary controller
adaptations are automatically made. This control optimization increase the ruggedness of
the control for weak grids, and increases rise and correction times.
Additional measures may be required in extreme cases:
● The measuring current is reduced if the automatic control optimization becomes unstable,
and is canceled with an overvoltage and/or overcurrent fault: Set p3415[0] = p3415[1] =
7 % and repeat the optimization with p3410 = 5.
● The gain factors for the grid current control and the DC link voltage control can be
reduced; in addition, the current precontrol can also be reduced. These measures
especially apply to applications with relatively low requirements placed on the dynamic
performance of the control systems without step-type load surges.
Typical settings include, for example
– p3560 = 25 % ... 50 % (small DC links, e.g.: 1 Active Line Module + 2 Motor Modules
– p3560 = 100 % ... 150 % (large DC links, e.g.: 4 Active Line Module + 4 Motor
– p3603 = 25 % ... 50 %
– p3615 = 50%
Especially for time-variable grid conditions, the controller can also be adapted
dynamically and in time synchronism via BiCo signal inputs (p3561, p3604, p3616).
● For operation on weak grids, frequently, the system – comprising inverter, grid filter and
the grid – manifests a resonance point at approximately 1/4 of the Active Line Module
controller frequency (0.25 / p0115[0]). For analysis, for example, high resolution traces
and FFT calculations of the phase currents (r0069) and filter voltages (r3661, r3662) can
be carried out.
To dampen the resonance, a bandstop filter can be configured for the Active Line Module
output voltage (p5201 ff). When required, a bandstop filter can be activated for the
current actual values (p5211 ff). All bandstop filters are preconfigured for a blocking (trap)
frequency of 1000 Hz.
● Normally, the Vdc controller of the Active Line Module corrects/cancels any DC link
voltage oscillations. If this is not possible as a result of the oscillation frequency, or is not
desirable for a specific application, then a bandstop filter can be configured for the Vdc
actual value (p1677 ff).
138
chassis format)
Modules chassis format)
System Manual, 04/2015, A5E03347436A
Grid infeed