Siemens SINAMICS PERFECT HARMONY GH180 Function Manual page 192

Operating the Control
7.4 Cell Bypass
Available voltage after failure with and without neutral shift
The following graph compares the available voltage after a failure with and without using
neutral shift. In many cases, the extra voltage available with neutral shift will determine whether
or not a cell failure can be tolerated.
Figure 7-9
The voltage capability of a drive after cell bypass can be calculated using the following
calculation:
If X is the largest number of cells in bypass in two of the phases, then the maximum voltage at
the drive output will be:
where:
Example
For a drive with 18 cells, each rated for 690 V the maximum output voltage that this drive can
deliver is 7.37 kV:
190
Available Voltage after a failure
Vout_bypass = Vout * (2*N - X) / (2*N)
Vout is maximum output voltage that the drive can deliver (Vout = 1.78*N*Vcell)
N is the number of ranks (i.e. number of installed cells = 3*N)
Vcell is the cell voltage rating
Vout = 1.78 * 6 * 690 = 7.37 kV
With N = 6 and Vcell = 690 V
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